webkitgtk-2.12.3webkitgtk-2.12.3

1 files changed, 315 insertions, 347 deletions

diff --git a/Source/JavaScriptCore/jit/ThunkGenerators.cpp b/Source/JavaScriptCore/jit/ThunkGenerators.cpp
index f8f5cbaf5..4a71dfeb2 100644
--- a/Source/JavaScriptCore/jit/ThunkGenerators.cpp
+++ b/Source/JavaScriptCore/jit/ThunkGenerators.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2010, 2012, 2013 Apple Inc. All rights reserved.
+ * Copyright (C) 2010, 2012, 2013, 2014 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -27,11 +27,14 @@
 #include "ThunkGenerators.h"
 
 #include "CodeBlock.h"
+#include "DFGSpeculativeJIT.h"
 #include "JITOperations.h"
 #include "JSArray.h"
 #include "JSArrayIterator.h"
 #include "JSStack.h"
-#include "Operations.h"
+#include "MathCommon.h"
+#include "MaxFrameExtentForSlowPathCall.h"
+#include "JSCInlines.h"
 #include "SpecializedThunkJIT.h"
 #include <wtf/InlineASM.h>
 #include <wtf/StringPrintStream.h>
@@ -43,17 +46,14 @@ namespace JSC {
 
 inline void emitPointerValidation(CCallHelpers& jit, GPRReg pointerGPR)
 {
-#if !ASSERT_DISABLED
+    if (ASSERT_DISABLED)
+        return;
     CCallHelpers::Jump isNonZero = jit.branchTestPtr(CCallHelpers::NonZero, pointerGPR);
-    jit.breakpoint();
+    jit.abortWithReason(TGInvalidPointer);
     isNonZero.link(&jit);
     jit.pushToSave(pointerGPR);
     jit.load8(pointerGPR, pointerGPR);
     jit.popToRestore(pointerGPR);
-#else
-    UNUSED_PARAM(jit);
-    UNUSED_PARAM(pointerGPR);
-#endif
 }
 
 // We will jump here if the JIT code tries to make a call, but the
@@ -66,86 +66,100 @@ MacroAssemblerCodeRef throwExceptionFromCallSlowPathGenerator(VM* vm)
     // even though we won't use it.
     jit.preserveReturnAddressAfterCall(GPRInfo::nonPreservedNonReturnGPR);
 
-    // The CallFrame register points to the (failed) callee frame, so we need to pop back one frame.
-    jit.emitGetCallerFrameFromCallFrameHeaderPtr(GPRInfo::callFrameRegister);
+    jit.copyCalleeSavesToVMCalleeSavesBuffer();
 
-    jit.setupArgumentsExecState();
+    jit.setupArguments(CCallHelpers::TrustedImmPtr(vm), GPRInfo::callFrameRegister);
     jit.move(CCallHelpers::TrustedImmPtr(bitwise_cast<void*>(lookupExceptionHandler)), GPRInfo::nonArgGPR0);
     emitPointerValidation(jit, GPRInfo::nonArgGPR0);
     jit.call(GPRInfo::nonArgGPR0);
     jit.jumpToExceptionHandler();
 
-    LinkBuffer patchBuffer(*vm, &jit, GLOBAL_THUNK_ID);
+    LinkBuffer patchBuffer(*vm, jit, GLOBAL_THUNK_ID);
     return FINALIZE_CODE(patchBuffer, ("Throw exception from call slow path thunk"));
 }
 
 static void slowPathFor(
-    CCallHelpers& jit, VM* vm, P_JITOperation_E slowPathFunction)
+    CCallHelpers& jit, VM* vm, Sprt_JITOperation_ECli slowPathFunction)
 {
-    jit.preserveReturnAddressAfterCall(GPRInfo::nonArgGPR2);
-    emitPointerValidation(jit, GPRInfo::nonArgGPR2);
-    jit.emitPutReturnPCToCallFrameHeader(GPRInfo::nonArgGPR2);
+    jit.emitFunctionPrologue();
     jit.storePtr(GPRInfo::callFrameRegister, &vm->topCallFrame);
-    jit.setupArgumentsExecState();
+#if OS(WINDOWS) && CPU(X86_64)
+    // Windows X86_64 needs some space pointed to by arg0 for return types larger than 64 bits.
+    // Other argument values are shift by 1. Use space on the stack for our two return values.
+    // Moving the stack down maxFrameExtentForSlowPathCall bytes gives us room for our 3 arguments
+    // and space for the 16 byte return area.
+    jit.addPtr(CCallHelpers::TrustedImm32(-maxFrameExtentForSlowPathCall), CCallHelpers::stackPointerRegister);
+    jit.move(GPRInfo::regT2, GPRInfo::argumentGPR2);
+    jit.addPtr(CCallHelpers::TrustedImm32(32), CCallHelpers::stackPointerRegister, GPRInfo::argumentGPR0);
+    jit.move(GPRInfo::callFrameRegister, GPRInfo::argumentGPR1);
     jit.move(CCallHelpers::TrustedImmPtr(bitwise_cast<void*>(slowPathFunction)), GPRInfo::nonArgGPR0);
     emitPointerValidation(jit, GPRInfo::nonArgGPR0);
     jit.call(GPRInfo::nonArgGPR0);
-    
+    jit.loadPtr(CCallHelpers::Address(GPRInfo::returnValueGPR, 8), GPRInfo::returnValueGPR2);
+    jit.loadPtr(CCallHelpers::Address(GPRInfo::returnValueGPR), GPRInfo::returnValueGPR);
+    jit.addPtr(CCallHelpers::TrustedImm32(maxFrameExtentForSlowPathCall), CCallHelpers::stackPointerRegister);
+#else
+    if (maxFrameExtentForSlowPathCall)
+        jit.addPtr(CCallHelpers::TrustedImm32(-maxFrameExtentForSlowPathCall), CCallHelpers::stackPointerRegister);
+    jit.setupArgumentsWithExecState(GPRInfo::regT2);
+    jit.move(CCallHelpers::TrustedImmPtr(bitwise_cast<void*>(slowPathFunction)), GPRInfo::nonArgGPR0);
+    emitPointerValidation(jit, GPRInfo::nonArgGPR0);
+    jit.call(GPRInfo::nonArgGPR0);
+    if (maxFrameExtentForSlowPathCall)
+        jit.addPtr(CCallHelpers::TrustedImm32(maxFrameExtentForSlowPathCall), CCallHelpers::stackPointerRegister);
+#endif
+
     // This slow call will return the address of one of the following:
     // 1) Exception throwing thunk.
     // 2) Host call return value returner thingy.
     // 3) The function to call.
-    jit.emitGetReturnPCFromCallFrameHeaderPtr(GPRInfo::nonPreservedNonReturnGPR);
-    jit.emitPutReturnPCToCallFrameHeader(CCallHelpers::TrustedImmPtr(0));
-    emitPointerValidation(jit, GPRInfo::nonPreservedNonReturnGPR);
-    jit.restoreReturnAddressBeforeReturn(GPRInfo::nonPreservedNonReturnGPR);
+    // The second return value GPR will hold a non-zero value for tail calls.
+
     emitPointerValidation(jit, GPRInfo::returnValueGPR);
+    jit.emitFunctionEpilogue();
+
+    RELEASE_ASSERT(reinterpret_cast<void*>(KeepTheFrame) == reinterpret_cast<void*>(0));
+    CCallHelpers::Jump doNotTrash = jit.branchTestPtr(CCallHelpers::Zero, GPRInfo::returnValueGPR2);
+
+    jit.preserveReturnAddressAfterCall(GPRInfo::nonPreservedNonReturnGPR);
+    jit.prepareForTailCallSlow(GPRInfo::returnValueGPR);
+
+    doNotTrash.link(&jit);
     jit.jump(GPRInfo::returnValueGPR);
 }
 
-static MacroAssemblerCodeRef linkForThunkGenerator(
-    VM* vm, CodeSpecializationKind kind)
+MacroAssemblerCodeRef linkCallThunkGenerator(VM* vm)
 {
     // The return address is on the stack or in the link register. We will hence
     // save the return address to the call frame while we make a C++ function call
     // to perform linking and lazy compilation if necessary. We expect the callee
     // to be in regT0/regT1 (payload/tag), the CallFrame to have already
     // been adjusted, and all other registers to be available for use.
-    
     CCallHelpers jit(vm);
     
-    slowPathFor(jit, vm, kind == CodeForCall ? operationLinkCall : operationLinkConstruct);
+    slowPathFor(jit, vm, operationLinkCall);
     
-    LinkBuffer patchBuffer(*vm, &jit, GLOBAL_THUNK_ID);
-    return FINALIZE_CODE(
-        patchBuffer,
-        ("Link %s slow path thunk", kind == CodeForCall ? "call" : "construct"));
-}
-
-MacroAssemblerCodeRef linkCallThunkGenerator(VM* vm)
-{
-    return linkForThunkGenerator(vm, CodeForCall);
-}
-
-MacroAssemblerCodeRef linkConstructThunkGenerator(VM* vm)
-{
-    return linkForThunkGenerator(vm, CodeForConstruct);
+    LinkBuffer patchBuffer(*vm, jit, GLOBAL_THUNK_ID);
+    return FINALIZE_CODE(patchBuffer, ("Link call slow path thunk"));
 }
 
 // For closure optimizations, we only include calls, since if you're using closures for
 // object construction then you're going to lose big time anyway.
-MacroAssemblerCodeRef linkClosureCallThunkGenerator(VM* vm)
+MacroAssemblerCodeRef linkPolymorphicCallThunkGenerator(VM* vm)
 {
     CCallHelpers jit(vm);
     
-    slowPathFor(jit, vm, operationLinkClosureCall);
+    slowPathFor(jit, vm, operationLinkPolymorphicCall);
     
-    LinkBuffer patchBuffer(*vm, &jit, GLOBAL_THUNK_ID);
-    return FINALIZE_CODE(patchBuffer, ("Link closure call slow path thunk"));
+    LinkBuffer patchBuffer(*vm, jit, GLOBAL_THUNK_ID);
+    return FINALIZE_CODE(patchBuffer, ("Link polymorphic call slow path thunk"));
 }
 
-static MacroAssemblerCodeRef virtualForThunkGenerator(
-    VM* vm, CodeSpecializationKind kind)
+// FIXME: We should distinguish between a megamorphic virtual call vs. a slow
+// path virtual call so that we can enable fast tail calls for megamorphic
+// virtual calls by using the shuffler.
+// https://bugs.webkit.org/show_bug.cgi?id=148831
+MacroAssemblerCodeRef virtualThunkFor(VM* vm, CallLinkInfo& callLinkInfo)
 {
     // The callee is in regT0 (for JSVALUE32_64, the tag is in regT1).
     // The return address is on the stack, or in the link register. We will hence
@@ -155,203 +169,149 @@ static MacroAssemblerCodeRef virtualForThunkGenerator(
     CCallHelpers jit(vm);
     
     CCallHelpers::JumpList slowCase;
+    
+    // This is a slow path execution, and regT2 contains the CallLinkInfo. Count the
+    // slow path execution for the profiler.
+    jit.add32(
+        CCallHelpers::TrustedImm32(1),
+        CCallHelpers::Address(GPRInfo::regT2, CallLinkInfo::offsetOfSlowPathCount()));
 
     // FIXME: we should have a story for eliminating these checks. In many cases,
     // the DFG knows that the value is definitely a cell, or definitely a function.
     
 #if USE(JSVALUE64)
+    jit.move(CCallHelpers::TrustedImm64(TagMask), GPRInfo::regT4);
+    
     slowCase.append(
         jit.branchTest64(
-            CCallHelpers::NonZero, GPRInfo::regT0, GPRInfo::tagMaskRegister));
+            CCallHelpers::NonZero, GPRInfo::regT0, GPRInfo::regT4));
 #else
     slowCase.append(
         jit.branch32(
             CCallHelpers::NotEqual, GPRInfo::regT1,
             CCallHelpers::TrustedImm32(JSValue::CellTag)));
 #endif
-    jit.loadPtr(CCallHelpers::Address(GPRInfo::regT0, JSCell::structureOffset()), GPRInfo::nonArgGPR2);
+    AssemblyHelpers::emitLoadStructure(jit, GPRInfo::regT0, GPRInfo::regT4, GPRInfo::regT1);
     slowCase.append(
         jit.branchPtr(
             CCallHelpers::NotEqual,
-            CCallHelpers::Address(GPRInfo::nonArgGPR2, Structure::classInfoOffset()),
+            CCallHelpers::Address(GPRInfo::regT4, Structure::classInfoOffset()),
             CCallHelpers::TrustedImmPtr(JSFunction::info())));
     
     // Now we know we have a JSFunction.
     
     jit.loadPtr(
         CCallHelpers::Address(GPRInfo::regT0, JSFunction::offsetOfExecutable()),
-        GPRInfo::nonArgGPR2);
-    slowCase.append(
-        jit.branch32(
-            CCallHelpers::LessThan,
-            CCallHelpers::Address(
-                GPRInfo::nonArgGPR2, ExecutableBase::offsetOfNumParametersFor(kind)),
-            CCallHelpers::TrustedImm32(0)));
-    
-    // Now we know that we have a CodeBlock, and we're committed to making a fast
-    // call.
-    
+        GPRInfo::regT4);
     jit.loadPtr(
-        CCallHelpers::Address(GPRInfo::regT0, JSFunction::offsetOfScopeChain()),
-        GPRInfo::regT1);
-#if USE(JSVALUE64)
-    jit.store64(
-        GPRInfo::regT1,
-        CCallHelpers::Address(
-            GPRInfo::callFrameRegister,
-            static_cast<ptrdiff_t>(sizeof(Register)) * JSStack::ScopeChain));
-#else
-    jit.storePtr(
-        GPRInfo::regT1,
         CCallHelpers::Address(
-            GPRInfo::callFrameRegister,
-            static_cast<ptrdiff_t>(sizeof(Register)) * JSStack::ScopeChain +
-            OBJECT_OFFSETOF(EncodedValueDescriptor, asBits.payload)));
-    jit.store32(
-        CCallHelpers::TrustedImm32(JSValue::CellTag),
-        CCallHelpers::Address(
-            GPRInfo::callFrameRegister,
-            static_cast<ptrdiff_t>(sizeof(Register)) * JSStack::ScopeChain +
-            OBJECT_OFFSETOF(EncodedValueDescriptor, asBits.tag)));
-#endif
+            GPRInfo::regT4, ExecutableBase::offsetOfJITCodeWithArityCheckFor(
+                callLinkInfo.specializationKind())),
+        GPRInfo::regT4);
+    slowCase.append(jit.branchTestPtr(CCallHelpers::Zero, GPRInfo::regT4));
     
-    jit.loadPtr(
-        CCallHelpers::Address(GPRInfo::nonArgGPR2, ExecutableBase::offsetOfJITCodeWithArityCheckFor(kind)),
-        GPRInfo::regT0);
+    // Now we know that we have a CodeBlock, and we're committed to making a fast
+    // call.
     
     // Make a tail call. This will return back to JIT code.
-    emitPointerValidation(jit, GPRInfo::regT0);
-    jit.jump(GPRInfo::regT0);
+    emitPointerValidation(jit, GPRInfo::regT4);
+    if (callLinkInfo.isTailCall()) {
+        jit.preserveReturnAddressAfterCall(GPRInfo::regT0);
+        jit.prepareForTailCallSlow(GPRInfo::regT4);
+    }
+    jit.jump(GPRInfo::regT4);
 
     slowCase.link(&jit);
     
     // Here we don't know anything, so revert to the full slow path.
     
-    slowPathFor(jit, vm, kind == CodeForCall ? operationVirtualCall : operationVirtualConstruct);
+    slowPathFor(jit, vm, operationVirtualCall);
     
-    LinkBuffer patchBuffer(*vm, &jit, GLOBAL_THUNK_ID);
+    LinkBuffer patchBuffer(*vm, jit, GLOBAL_THUNK_ID);
     return FINALIZE_CODE(
         patchBuffer,
-        ("Virtual %s slow path thunk", kind == CodeForCall ? "call" : "construct"));
+        ("Virtual %s slow path thunk",
+        callLinkInfo.callMode() == CallMode::Regular ? "call" : callLinkInfo.callMode() == CallMode::Tail ? "tail call" : "construct"));
 }
 
-MacroAssemblerCodeRef virtualCallThunkGenerator(VM* vm)
-{
-    return virtualForThunkGenerator(vm, CodeForCall);
-}
+enum ThunkEntryType { EnterViaCall, EnterViaJump };
 
-MacroAssemblerCodeRef virtualConstructThunkGenerator(VM* vm)
-{
-    return virtualForThunkGenerator(vm, CodeForConstruct);
-}
-
-static MacroAssemblerCodeRef nativeForGenerator(VM* vm, CodeSpecializationKind kind)
+static MacroAssemblerCodeRef nativeForGenerator(VM* vm, CodeSpecializationKind kind, ThunkEntryType entryType = EnterViaCall)
 {
     int executableOffsetToFunction = NativeExecutable::offsetOfNativeFunctionFor(kind);
     
     JSInterfaceJIT jit(vm);
-    
-    jit.emitPutImmediateToCallFrameHeader(0, JSStack::CodeBlock);
-    jit.storePtr(JSInterfaceJIT::callFrameRegister, &vm->topCallFrame);
 
-#if CPU(X86)
-    // Load caller frame's scope chain into this callframe so that whatever we call can
-    // get to its global data.
-    jit.emitGetCallerFrameFromCallFrameHeaderPtr(JSInterfaceJIT::regT0);
-    jit.emitGetFromCallFrameHeaderPtr(JSStack::ScopeChain, JSInterfaceJIT::regT1, JSInterfaceJIT::regT0);
-    jit.emitPutCellToCallFrameHeader(JSInterfaceJIT::regT1, JSStack::ScopeChain);
+    if (entryType == EnterViaCall)
+        jit.emitFunctionPrologue();
+#if USE(JSVALUE64)
+    else if (entryType == EnterViaJump) {
+        // We're coming from a specialized thunk that has saved the prior tag registers' contents.
+        // Restore them now.
+#if CPU(ARM64)
+        jit.popPair(JSInterfaceJIT::tagTypeNumberRegister, JSInterfaceJIT::tagMaskRegister);
+#else
+        jit.pop(JSInterfaceJIT::tagMaskRegister);
+        jit.pop(JSInterfaceJIT::tagTypeNumberRegister);
+#endif
+    }
+#endif
 
-    jit.peek(JSInterfaceJIT::regT1);
-    jit.emitPutReturnPCToCallFrameHeader(JSInterfaceJIT::regT1);
+    jit.emitPutToCallFrameHeader(0, JSStack::CodeBlock);
+    jit.storePtr(JSInterfaceJIT::callFrameRegister, &vm->topCallFrame);
 
+#if CPU(X86)
     // Calling convention:      f(ecx, edx, ...);
     // Host function signature: f(ExecState*);
     jit.move(JSInterfaceJIT::callFrameRegister, X86Registers::ecx);
 
-    jit.subPtr(JSInterfaceJIT::TrustedImm32(16 - sizeof(void*)), JSInterfaceJIT::stackPointerRegister); // Align stack after call.
+    jit.subPtr(JSInterfaceJIT::TrustedImm32(8), JSInterfaceJIT::stackPointerRegister); // Align stack after prologue.
 
     // call the function
     jit.emitGetFromCallFrameHeaderPtr(JSStack::Callee, JSInterfaceJIT::regT1);
     jit.loadPtr(JSInterfaceJIT::Address(JSInterfaceJIT::regT1, JSFunction::offsetOfExecutable()), JSInterfaceJIT::regT1);
-    jit.move(JSInterfaceJIT::regT0, JSInterfaceJIT::callFrameRegister); // Eagerly restore caller frame register to avoid loading from stack.
     jit.call(JSInterfaceJIT::Address(JSInterfaceJIT::regT1, executableOffsetToFunction));
 
-    jit.addPtr(JSInterfaceJIT::TrustedImm32(16 - sizeof(void*)), JSInterfaceJIT::stackPointerRegister);
+    jit.addPtr(JSInterfaceJIT::TrustedImm32(8), JSInterfaceJIT::stackPointerRegister);
 
 #elif CPU(X86_64)
-    // Load caller frame's scope chain into this callframe so that whatever we call can
-    // get to its global data.
-    jit.emitGetCallerFrameFromCallFrameHeaderPtr(JSInterfaceJIT::regT0);
-    jit.emitGetFromCallFrameHeaderPtr(JSStack::ScopeChain, JSInterfaceJIT::regT1, JSInterfaceJIT::regT0);
-    jit.emitPutCellToCallFrameHeader(JSInterfaceJIT::regT1, JSStack::ScopeChain);
-
-    jit.peek(JSInterfaceJIT::regT1);
-    jit.emitPutReturnPCToCallFrameHeader(JSInterfaceJIT::regT1);
-
 #if !OS(WINDOWS)
     // Calling convention:      f(edi, esi, edx, ecx, ...);
     // Host function signature: f(ExecState*);
     jit.move(JSInterfaceJIT::callFrameRegister, X86Registers::edi);
 
-    jit.subPtr(JSInterfaceJIT::TrustedImm32(16 - sizeof(int64_t)), JSInterfaceJIT::stackPointerRegister); // Align stack after call.
-
     jit.emitGetFromCallFrameHeaderPtr(JSStack::Callee, X86Registers::esi);
     jit.loadPtr(JSInterfaceJIT::Address(X86Registers::esi, JSFunction::offsetOfExecutable()), X86Registers::r9);
-    jit.move(JSInterfaceJIT::regT0, JSInterfaceJIT::callFrameRegister); // Eagerly restore caller frame register to avoid loading from stack.
     jit.call(JSInterfaceJIT::Address(X86Registers::r9, executableOffsetToFunction));
 
-    jit.addPtr(JSInterfaceJIT::TrustedImm32(16 - sizeof(int64_t)), JSInterfaceJIT::stackPointerRegister);
 #else
     // Calling convention:      f(ecx, edx, r8, r9, ...);
     // Host function signature: f(ExecState*);
     jit.move(JSInterfaceJIT::callFrameRegister, X86Registers::ecx);
 
-    // Leave space for the callee parameter home addresses and align the stack.
-    jit.subPtr(JSInterfaceJIT::TrustedImm32(4 * sizeof(int64_t) + 16 - sizeof(int64_t)), JSInterfaceJIT::stackPointerRegister);
+    // Leave space for the callee parameter home addresses.
+    // At this point the stack is aligned to 16 bytes, but if this changes at some point, we need to emit code to align it.
+    jit.subPtr(JSInterfaceJIT::TrustedImm32(4 * sizeof(int64_t)), JSInterfaceJIT::stackPointerRegister);
 
     jit.emitGetFromCallFrameHeaderPtr(JSStack::Callee, X86Registers::edx);
     jit.loadPtr(JSInterfaceJIT::Address(X86Registers::edx, JSFunction::offsetOfExecutable()), X86Registers::r9);
-    jit.move(JSInterfaceJIT::regT0, JSInterfaceJIT::callFrameRegister); // Eagerly restore caller frame register to avoid loading from stack.
     jit.call(JSInterfaceJIT::Address(X86Registers::r9, executableOffsetToFunction));
 
-    jit.addPtr(JSInterfaceJIT::TrustedImm32(4 * sizeof(int64_t) + 16 - sizeof(int64_t)), JSInterfaceJIT::stackPointerRegister);
+    jit.addPtr(JSInterfaceJIT::TrustedImm32(4 * sizeof(int64_t)), JSInterfaceJIT::stackPointerRegister);
 #endif
 
 #elif CPU(ARM64)
-    COMPILE_ASSERT(ARM64Registers::x3 != JSInterfaceJIT::regT1, prev_callframe_not_trampled_by_T1);
-    COMPILE_ASSERT(ARM64Registers::x3 != JSInterfaceJIT::regT3, prev_callframe_not_trampled_by_T3);
     COMPILE_ASSERT(ARM64Registers::x0 != JSInterfaceJIT::regT3, T3_not_trampled_by_arg_0);
     COMPILE_ASSERT(ARM64Registers::x1 != JSInterfaceJIT::regT3, T3_not_trampled_by_arg_1);
     COMPILE_ASSERT(ARM64Registers::x2 != JSInterfaceJIT::regT3, T3_not_trampled_by_arg_2);
 
-    // Load caller frame's scope chain into this callframe so that whatever we call can
-    // get to its global data.
-    jit.emitGetCallerFrameFromCallFrameHeaderPtr(ARM64Registers::x3);
-    jit.emitGetFromCallFrameHeaderPtr(JSStack::ScopeChain, JSInterfaceJIT::regT1, ARM64Registers::x3);
-    jit.emitPutCellToCallFrameHeader(JSInterfaceJIT::regT1, JSStack::ScopeChain);
-
-    jit.preserveReturnAddressAfterCall(JSInterfaceJIT::regT3); // Callee preserved
-    jit.emitPutReturnPCToCallFrameHeader(ARM64Registers::lr);
-
     // Host function signature: f(ExecState*);
     jit.move(JSInterfaceJIT::callFrameRegister, ARM64Registers::x0);
 
     jit.emitGetFromCallFrameHeaderPtr(JSStack::Callee, ARM64Registers::x1);
     jit.loadPtr(JSInterfaceJIT::Address(ARM64Registers::x1, JSFunction::offsetOfExecutable()), ARM64Registers::x2);
-    jit.move(ARM64Registers::x3, JSInterfaceJIT::callFrameRegister); // Eagerly restore caller frame register to avoid loading from stack.
     jit.call(JSInterfaceJIT::Address(ARM64Registers::x2, executableOffsetToFunction));
-
-    jit.restoreReturnAddressBeforeReturn(JSInterfaceJIT::regT3);
-
 #elif CPU(ARM) || CPU(SH4) || CPU(MIPS)
-    // Load caller frame's scope chain into this callframe so that whatever we call can get to its global data.
-    jit.emitGetCallerFrameFromCallFrameHeaderPtr(JSInterfaceJIT::regT2);
-    jit.emitGetFromCallFrameHeaderPtr(JSStack::ScopeChain, JSInterfaceJIT::regT1, JSInterfaceJIT::regT2);
-    jit.emitPutCellToCallFrameHeader(JSInterfaceJIT::regT1, JSStack::ScopeChain);
-
-    jit.preserveReturnAddressAfterCall(JSInterfaceJIT::regT3); // Callee preserved
-    jit.emitPutReturnPCToCallFrameHeader(JSInterfaceJIT::regT3);
-
 #if CPU(MIPS)
     // Allocate stack space for (unused) 16 bytes (8-byte aligned) for 4 arguments.
     jit.subPtr(JSInterfaceJIT::TrustedImm32(16), JSInterfaceJIT::stackPointerRegister);
@@ -362,7 +322,6 @@ static MacroAssemblerCodeRef nativeForGenerator(VM* vm, CodeSpecializationKind k
     jit.move(JSInterfaceJIT::callFrameRegister, JSInterfaceJIT::argumentGPR0);
 
     jit.emitGetFromCallFrameHeaderPtr(JSStack::Callee, JSInterfaceJIT::argumentGPR1);
-    jit.move(JSInterfaceJIT::regT2, JSInterfaceJIT::callFrameRegister); // Eagerly restore caller frame register to avoid loading from stack.
     jit.loadPtr(JSInterfaceJIT::Address(JSInterfaceJIT::argumentGPR1, JSFunction::offsetOfExecutable()), JSInterfaceJIT::regT2);
     jit.call(JSInterfaceJIT::Address(JSInterfaceJIT::regT2, executableOffsetToFunction));
 
@@ -370,12 +329,10 @@ static MacroAssemblerCodeRef nativeForGenerator(VM* vm, CodeSpecializationKind k
     // Restore stack space
     jit.addPtr(JSInterfaceJIT::TrustedImm32(16), JSInterfaceJIT::stackPointerRegister);
 #endif
-
-    jit.restoreReturnAddressBeforeReturn(JSInterfaceJIT::regT3);
 #else
 #error "JIT not supported on this platform."
     UNUSED_PARAM(executableOffsetToFunction);
-    breakpoint();
+    abortWithReason(TGNotSupported);
 #endif
 
     // Check for an exception
@@ -385,40 +342,43 @@ static MacroAssemblerCodeRef nativeForGenerator(VM* vm, CodeSpecializationKind k
 #else
     JSInterfaceJIT::Jump exceptionHandler = jit.branch32(
         JSInterfaceJIT::NotEqual,
-        JSInterfaceJIT::AbsoluteAddress(reinterpret_cast<char*>(vm->addressOfException()) + OBJECT_OFFSETOF(EncodedValueDescriptor, asBits.tag)),
-        JSInterfaceJIT::TrustedImm32(JSValue::EmptyValueTag));
+        JSInterfaceJIT::AbsoluteAddress(vm->addressOfException()),
+        JSInterfaceJIT::TrustedImm32(0));
 #endif
 
+    jit.emitFunctionEpilogue();
     // Return.
     jit.ret();
 
     // Handle an exception
     exceptionHandler.link(&jit);
 
-    // Grab the return address.
-    jit.preserveReturnAddressAfterCall(JSInterfaceJIT::regT1);
-    
-    jit.move(JSInterfaceJIT::TrustedImmPtr(&vm->exceptionLocation), JSInterfaceJIT::regT2);
-    jit.storePtr(JSInterfaceJIT::regT1, JSInterfaceJIT::regT2);
-
+    jit.copyCalleeSavesToVMCalleeSavesBuffer();
     jit.storePtr(JSInterfaceJIT::callFrameRegister, &vm->topCallFrame);
 
 #if CPU(X86) && USE(JSVALUE32_64)
     jit.addPtr(JSInterfaceJIT::TrustedImm32(-12), JSInterfaceJIT::stackPointerRegister);
-    jit.push(JSInterfaceJIT::callFrameRegister);
+    jit.move(JSInterfaceJIT::callFrameRegister, JSInterfaceJIT::regT0);
+    jit.push(JSInterfaceJIT::regT0);
 #else
+#if OS(WINDOWS)
+    // Allocate space on stack for the 4 parameter registers.
+    jit.subPtr(JSInterfaceJIT::TrustedImm32(4 * sizeof(int64_t)), JSInterfaceJIT::stackPointerRegister);
+#endif
     jit.move(JSInterfaceJIT::callFrameRegister, JSInterfaceJIT::argumentGPR0);
 #endif
     jit.move(JSInterfaceJIT::TrustedImmPtr(FunctionPtr(operationVMHandleException).value()), JSInterfaceJIT::regT3);
     jit.call(JSInterfaceJIT::regT3);
 #if CPU(X86) && USE(JSVALUE32_64)
     jit.addPtr(JSInterfaceJIT::TrustedImm32(16), JSInterfaceJIT::stackPointerRegister);
+#elif OS(WINDOWS)
+    jit.addPtr(JSInterfaceJIT::TrustedImm32(4 * sizeof(int64_t)), JSInterfaceJIT::stackPointerRegister);
 #endif
 
     jit.jumpToExceptionHandler();
 
-    LinkBuffer patchBuffer(*vm, &jit, GLOBAL_THUNK_ID);
-    return FINALIZE_CODE(patchBuffer, ("native %s trampoline", toCString(kind).data()));
+    LinkBuffer patchBuffer(*vm, jit, GLOBAL_THUNK_ID);
+    return FINALIZE_CODE(patchBuffer, ("native %s%s trampoline", entryType == EnterViaJump ? "Tail " : "", toCString(kind).data()));
 }
 
 MacroAssemblerCodeRef nativeCallGenerator(VM* vm)
@@ -426,43 +386,72 @@ MacroAssemblerCodeRef nativeCallGenerator(VM* vm)
     return nativeForGenerator(vm, CodeForCall);
 }
 
+MacroAssemblerCodeRef nativeTailCallGenerator(VM* vm)
+{
+    return nativeForGenerator(vm, CodeForCall, EnterViaJump);
+}
+
 MacroAssemblerCodeRef nativeConstructGenerator(VM* vm)
 {
     return nativeForGenerator(vm, CodeForConstruct);
 }
 
-MacroAssemblerCodeRef arityFixup(VM* vm)
+MacroAssemblerCodeRef arityFixupGenerator(VM* vm)
 {
     JSInterfaceJIT jit(vm);
 
-    // We enter with fixup count in regT0
+    // We enter with fixup count in argumentGPR0
+    // We have the guarantee that a0, a1, a2, t3, t4 and t5 (or t0 for Windows) are all distinct :-)
 #if USE(JSVALUE64)
+#if OS(WINDOWS)
+    const GPRReg extraTemp = JSInterfaceJIT::regT0;
+#else
+    const GPRReg extraTemp = JSInterfaceJIT::regT5;
+#endif
 #  if CPU(X86_64)
     jit.pop(JSInterfaceJIT::regT4);
 #  endif
-    jit.neg64(JSInterfaceJIT::regT0);
     jit.move(JSInterfaceJIT::callFrameRegister, JSInterfaceJIT::regT3);
-    jit.load32(JSInterfaceJIT::Address(JSInterfaceJIT::callFrameRegister, JSStack::ArgumentCount * 8), JSInterfaceJIT::regT2);
-    jit.add32(JSInterfaceJIT::TrustedImm32(JSStack::CallFrameHeaderSize), JSInterfaceJIT::regT2);
-
-    // Move current frame down regT0 number of slots
+    jit.load32(JSInterfaceJIT::Address(JSInterfaceJIT::callFrameRegister, JSStack::ArgumentCount * sizeof(Register)), JSInterfaceJIT::argumentGPR2);
+    jit.add32(JSInterfaceJIT::TrustedImm32(JSStack::CallFrameHeaderSize), JSInterfaceJIT::argumentGPR2);
+
+    // Check to see if we have extra slots we can use
+    jit.move(JSInterfaceJIT::argumentGPR0, JSInterfaceJIT::argumentGPR1);
+    jit.and32(JSInterfaceJIT::TrustedImm32(stackAlignmentRegisters() - 1), JSInterfaceJIT::argumentGPR1);
+    JSInterfaceJIT::Jump noExtraSlot = jit.branchTest32(MacroAssembler::Zero, JSInterfaceJIT::argumentGPR1);
+    jit.move(JSInterfaceJIT::TrustedImm64(ValueUndefined), extraTemp);
+    JSInterfaceJIT::Label fillExtraSlots(jit.label());
+    jit.store64(extraTemp, MacroAssembler::BaseIndex(JSInterfaceJIT::callFrameRegister, JSInterfaceJIT::argumentGPR2, JSInterfaceJIT::TimesEight));
+    jit.add32(JSInterfaceJIT::TrustedImm32(1), JSInterfaceJIT::argumentGPR2);
+    jit.branchSub32(JSInterfaceJIT::NonZero, JSInterfaceJIT::TrustedImm32(1), JSInterfaceJIT::argumentGPR1).linkTo(fillExtraSlots, &jit);
+    jit.and32(JSInterfaceJIT::TrustedImm32(-stackAlignmentRegisters()), JSInterfaceJIT::argumentGPR0);
+    JSInterfaceJIT::Jump done = jit.branchTest32(MacroAssembler::Zero, JSInterfaceJIT::argumentGPR0);
+    noExtraSlot.link(&jit);
+
+    jit.neg64(JSInterfaceJIT::argumentGPR0);
+
+    // Move current frame down argumentGPR0 number of slots
     JSInterfaceJIT::Label copyLoop(jit.label());
-    jit.load64(JSInterfaceJIT::regT3, JSInterfaceJIT::regT1);
-    jit.store64(JSInterfaceJIT::regT1, MacroAssembler::BaseIndex(JSInterfaceJIT::regT3, JSInterfaceJIT::regT0, JSInterfaceJIT::TimesEight));
+    jit.load64(JSInterfaceJIT::regT3, extraTemp);
+    jit.store64(extraTemp, MacroAssembler::BaseIndex(JSInterfaceJIT::regT3, JSInterfaceJIT::argumentGPR0, JSInterfaceJIT::TimesEight));
     jit.addPtr(JSInterfaceJIT::TrustedImm32(8), JSInterfaceJIT::regT3);
-    jit.branchSub32(MacroAssembler::NonZero, JSInterfaceJIT::TrustedImm32(1), JSInterfaceJIT::regT2).linkTo(copyLoop, &jit);
+    jit.branchSub32(MacroAssembler::NonZero, JSInterfaceJIT::TrustedImm32(1), JSInterfaceJIT::argumentGPR2).linkTo(copyLoop, &jit);
 
-    // Fill in regT0 missing arg slots with undefined
-    jit.move(JSInterfaceJIT::regT0, JSInterfaceJIT::regT2);
-    jit.move(JSInterfaceJIT::TrustedImm64(ValueUndefined), JSInterfaceJIT::regT1);
+    // Fill in argumentGPR0 missing arg slots with undefined
+    jit.move(JSInterfaceJIT::argumentGPR0, JSInterfaceJIT::argumentGPR2);
+    jit.move(JSInterfaceJIT::TrustedImm64(ValueUndefined), extraTemp);
     JSInterfaceJIT::Label fillUndefinedLoop(jit.label());
-    jit.store64(JSInterfaceJIT::regT1, MacroAssembler::BaseIndex(JSInterfaceJIT::regT3, JSInterfaceJIT::regT0, JSInterfaceJIT::TimesEight));
+    jit.store64(extraTemp, MacroAssembler::BaseIndex(JSInterfaceJIT::regT3, JSInterfaceJIT::argumentGPR0, JSInterfaceJIT::TimesEight));
     jit.addPtr(JSInterfaceJIT::TrustedImm32(8), JSInterfaceJIT::regT3);
-    jit.branchAdd32(MacroAssembler::NonZero, JSInterfaceJIT::TrustedImm32(1), JSInterfaceJIT::regT2).linkTo(fillUndefinedLoop, &jit);
+    jit.branchAdd32(MacroAssembler::NonZero, JSInterfaceJIT::TrustedImm32(1), JSInterfaceJIT::argumentGPR2).linkTo(fillUndefinedLoop, &jit);
+    
+    // Adjust call frame register and stack pointer to account for missing args
+    jit.move(JSInterfaceJIT::argumentGPR0, extraTemp);
+    jit.lshift64(JSInterfaceJIT::TrustedImm32(3), extraTemp);
+    jit.addPtr(extraTemp, JSInterfaceJIT::callFrameRegister);
+    jit.addPtr(extraTemp, JSInterfaceJIT::stackPointerRegister);
 
-    // Adjust call frame register to account for missing args
-    jit.lshift64(JSInterfaceJIT::TrustedImm32(3), JSInterfaceJIT::regT0);
-    jit.addPtr(JSInterfaceJIT::regT0, JSInterfaceJIT::callFrameRegister);
+    done.link(&jit);
 
 #  if CPU(X86_64)
     jit.push(JSInterfaceJIT::regT4);
@@ -472,34 +461,54 @@ MacroAssemblerCodeRef arityFixup(VM* vm)
 #  if CPU(X86)
     jit.pop(JSInterfaceJIT::regT4);
 #  endif
-    jit.neg32(JSInterfaceJIT::regT0);
     jit.move(JSInterfaceJIT::callFrameRegister, JSInterfaceJIT::regT3);
-    jit.load32(JSInterfaceJIT::Address(JSInterfaceJIT::callFrameRegister, JSStack::ArgumentCount * 8), JSInterfaceJIT::regT2);
-    jit.add32(JSInterfaceJIT::TrustedImm32(JSStack::CallFrameHeaderSize), JSInterfaceJIT::regT2);
-
-    // Move current frame down regT0 number of slots
+    jit.load32(JSInterfaceJIT::Address(JSInterfaceJIT::callFrameRegister, JSStack::ArgumentCount * sizeof(Register)), JSInterfaceJIT::argumentGPR2);
+    jit.add32(JSInterfaceJIT::TrustedImm32(JSStack::CallFrameHeaderSize), JSInterfaceJIT::argumentGPR2);
+
+    // Check to see if we have extra slots we can use
+    jit.move(JSInterfaceJIT::argumentGPR0, JSInterfaceJIT::argumentGPR1);
+    jit.and32(JSInterfaceJIT::TrustedImm32(stackAlignmentRegisters() - 1), JSInterfaceJIT::argumentGPR1);
+    JSInterfaceJIT::Jump noExtraSlot = jit.branchTest32(MacroAssembler::Zero, JSInterfaceJIT::argumentGPR1);
+    JSInterfaceJIT::Label fillExtraSlots(jit.label());
+    jit.move(JSInterfaceJIT::TrustedImm32(0), JSInterfaceJIT::regT5);
+    jit.store32(JSInterfaceJIT::regT5, MacroAssembler::BaseIndex(JSInterfaceJIT::callFrameRegister, JSInterfaceJIT::argumentGPR2, JSInterfaceJIT::TimesEight, PayloadOffset));
+    jit.move(JSInterfaceJIT::TrustedImm32(JSValue::UndefinedTag), JSInterfaceJIT::regT5);
+    jit.store32(JSInterfaceJIT::regT5, MacroAssembler::BaseIndex(JSInterfaceJIT::callFrameRegister, JSInterfaceJIT::argumentGPR2, JSInterfaceJIT::TimesEight, TagOffset));
+    jit.add32(JSInterfaceJIT::TrustedImm32(1), JSInterfaceJIT::argumentGPR2);
+    jit.branchSub32(JSInterfaceJIT::NonZero, JSInterfaceJIT::TrustedImm32(1), JSInterfaceJIT::argumentGPR1).linkTo(fillExtraSlots, &jit);
+    jit.and32(JSInterfaceJIT::TrustedImm32(-stackAlignmentRegisters()), JSInterfaceJIT::argumentGPR0);
+    JSInterfaceJIT::Jump done = jit.branchTest32(MacroAssembler::Zero, JSInterfaceJIT::argumentGPR0);
+    noExtraSlot.link(&jit);
+
+    jit.neg32(JSInterfaceJIT::argumentGPR0);
+
+    // Move current frame down argumentGPR0 number of slots
     JSInterfaceJIT::Label copyLoop(jit.label());
-    jit.load32(JSInterfaceJIT::regT3, JSInterfaceJIT::regT1);
-    jit.store32(JSInterfaceJIT::regT1, MacroAssembler::BaseIndex(JSInterfaceJIT::regT3, JSInterfaceJIT::regT0, JSInterfaceJIT::TimesEight));
-    jit.load32(MacroAssembler::Address(JSInterfaceJIT::regT3, 4), JSInterfaceJIT::regT1);
-    jit.store32(JSInterfaceJIT::regT1, MacroAssembler::BaseIndex(JSInterfaceJIT::regT3, JSInterfaceJIT::regT0, JSInterfaceJIT::TimesEight, 4));
+    jit.load32(MacroAssembler::Address(JSInterfaceJIT::regT3, PayloadOffset), JSInterfaceJIT::regT5);
+    jit.store32(JSInterfaceJIT::regT5, MacroAssembler::BaseIndex(JSInterfaceJIT::regT3, JSInterfaceJIT::argumentGPR0, JSInterfaceJIT::TimesEight, PayloadOffset));
+    jit.load32(MacroAssembler::Address(JSInterfaceJIT::regT3, TagOffset), JSInterfaceJIT::regT5);
+    jit.store32(JSInterfaceJIT::regT5, MacroAssembler::BaseIndex(JSInterfaceJIT::regT3, JSInterfaceJIT::argumentGPR0, JSInterfaceJIT::TimesEight, TagOffset));
     jit.addPtr(JSInterfaceJIT::TrustedImm32(8), JSInterfaceJIT::regT3);
-    jit.branchSub32(MacroAssembler::NonZero, JSInterfaceJIT::TrustedImm32(1), JSInterfaceJIT::regT2).linkTo(copyLoop, &jit);
+    jit.branchSub32(MacroAssembler::NonZero, JSInterfaceJIT::TrustedImm32(1), JSInterfaceJIT::argumentGPR2).linkTo(copyLoop, &jit);
 
-    // Fill in regT0 missing arg slots with undefined
-    jit.move(JSInterfaceJIT::regT0, JSInterfaceJIT::regT2);
+    // Fill in argumentGPR0 missing arg slots with undefined
+    jit.move(JSInterfaceJIT::argumentGPR0, JSInterfaceJIT::argumentGPR2);
     JSInterfaceJIT::Label fillUndefinedLoop(jit.label());
-    jit.move(JSInterfaceJIT::TrustedImm32(0), JSInterfaceJIT::regT1);
-    jit.store32(JSInterfaceJIT::regT1, MacroAssembler::BaseIndex(JSInterfaceJIT::regT3, JSInterfaceJIT::regT0, JSInterfaceJIT::TimesEight));
-    jit.move(JSInterfaceJIT::TrustedImm32(JSValue::UndefinedTag), JSInterfaceJIT::regT1);
-    jit.store32(JSInterfaceJIT::regT1, MacroAssembler::BaseIndex(JSInterfaceJIT::regT3, JSInterfaceJIT::regT0, JSInterfaceJIT::TimesEight, 4));
+    jit.move(JSInterfaceJIT::TrustedImm32(0), JSInterfaceJIT::regT5);
+    jit.store32(JSInterfaceJIT::regT5, MacroAssembler::BaseIndex(JSInterfaceJIT::regT3, JSInterfaceJIT::argumentGPR0, JSInterfaceJIT::TimesEight, PayloadOffset));
+    jit.move(JSInterfaceJIT::TrustedImm32(JSValue::UndefinedTag), JSInterfaceJIT::regT5);
+    jit.store32(JSInterfaceJIT::regT5, MacroAssembler::BaseIndex(JSInterfaceJIT::regT3, JSInterfaceJIT::argumentGPR0, JSInterfaceJIT::TimesEight, TagOffset));
 
     jit.addPtr(JSInterfaceJIT::TrustedImm32(8), JSInterfaceJIT::regT3);
-    jit.branchAdd32(MacroAssembler::NonZero, JSInterfaceJIT::TrustedImm32(1), JSInterfaceJIT::regT2).linkTo(fillUndefinedLoop, &jit);
+    jit.branchAdd32(MacroAssembler::NonZero, JSInterfaceJIT::TrustedImm32(1), JSInterfaceJIT::argumentGPR2).linkTo(fillUndefinedLoop, &jit);
+
+    // Adjust call frame register and stack pointer to account for missing args
+    jit.move(JSInterfaceJIT::argumentGPR0, JSInterfaceJIT::regT5);
+    jit.lshift32(JSInterfaceJIT::TrustedImm32(3), JSInterfaceJIT::regT5);
+    jit.addPtr(JSInterfaceJIT::regT5, JSInterfaceJIT::callFrameRegister);
+    jit.addPtr(JSInterfaceJIT::regT5, JSInterfaceJIT::stackPointerRegister);
 
-    // Adjust call frame register to account for missing args
-    jit.lshift32(JSInterfaceJIT::TrustedImm32(3), JSInterfaceJIT::regT0);
-    jit.addPtr(JSInterfaceJIT::regT0, JSInterfaceJIT::callFrameRegister);
+    done.link(&jit);
 
 #  if CPU(X86)
     jit.push(JSInterfaceJIT::regT4);
@@ -507,10 +516,20 @@ MacroAssemblerCodeRef arityFixup(VM* vm)
     jit.ret();
 #endif
 
-    LinkBuffer patchBuffer(*vm, &jit, GLOBAL_THUNK_ID);
+    LinkBuffer patchBuffer(*vm, jit, GLOBAL_THUNK_ID);
     return FINALIZE_CODE(patchBuffer, ("fixup arity"));
 }
 
+MacroAssemblerCodeRef unreachableGenerator(VM* vm)
+{
+    JSInterfaceJIT jit(vm);
+
+    jit.breakpoint();
+
+    LinkBuffer patchBuffer(*vm, jit, GLOBAL_THUNK_ID);
+    return FINALIZE_CODE(patchBuffer, ("unreachable thunk"));
+}
+
 static void stringCharLoad(SpecializedThunkJIT& jit, VM* vm)
 {
     // load string
@@ -554,7 +573,7 @@ MacroAssemblerCodeRef charCodeAtThunkGenerator(VM* vm)
     SpecializedThunkJIT jit(vm, 1);
     stringCharLoad(jit, vm);
     jit.returnInt32(SpecializedThunkJIT::regT0);
-    return jit.finalize(vm->jitStubs->ctiNativeCall(vm), "charCodeAt");
+    return jit.finalize(vm->jitStubs->ctiNativeTailCall(vm), "charCodeAt");
 }
 
 MacroAssemblerCodeRef charAtThunkGenerator(VM* vm)
@@ -563,7 +582,7 @@ MacroAssemblerCodeRef charAtThunkGenerator(VM* vm)
     stringCharLoad(jit, vm);
     charToString(jit, vm, SpecializedThunkJIT::regT0, SpecializedThunkJIT::regT0, SpecializedThunkJIT::regT1);
     jit.returnJSCell(SpecializedThunkJIT::regT0);
-    return jit.finalize(vm->jitStubs->ctiNativeCall(vm), "charAt");
+    return jit.finalize(vm->jitStubs->ctiNativeTailCall(vm), "charAt");
 }
 
 MacroAssemblerCodeRef fromCharCodeThunkGenerator(VM* vm)
@@ -573,7 +592,28 @@ MacroAssemblerCodeRef fromCharCodeThunkGenerator(VM* vm)
     jit.loadInt32Argument(0, SpecializedThunkJIT::regT0);
     charToString(jit, vm, SpecializedThunkJIT::regT0, SpecializedThunkJIT::regT0, SpecializedThunkJIT::regT1);
     jit.returnJSCell(SpecializedThunkJIT::regT0);
-    return jit.finalize(vm->jitStubs->ctiNativeCall(vm), "fromCharCode");
+    return jit.finalize(vm->jitStubs->ctiNativeTailCall(vm), "fromCharCode");
+}
+
+MacroAssemblerCodeRef clz32ThunkGenerator(VM* vm)
+{
+    SpecializedThunkJIT jit(vm, 1);
+    MacroAssembler::Jump nonIntArgJump;
+    jit.loadInt32Argument(0, SpecializedThunkJIT::regT0, nonIntArgJump);
+
+    SpecializedThunkJIT::Label convertedArgumentReentry(&jit);
+    jit.countLeadingZeros32(SpecializedThunkJIT::regT0, SpecializedThunkJIT::regT1);
+    jit.returnInt32(SpecializedThunkJIT::regT1);
+
+    if (jit.supportsFloatingPointTruncate()) {
+        nonIntArgJump.link(&jit);
+        jit.loadDoubleArgument(0, SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::regT0);
+        jit.branchTruncateDoubleToInt32(SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::regT0, SpecializedThunkJIT::BranchIfTruncateSuccessful).linkTo(convertedArgumentReentry, &jit);
+        jit.appendFailure(jit.jump());
+    } else
+        jit.appendFailure(nonIntArgJump);
+
+    return jit.finalize(vm->jitStubs->ctiNativeTailCall(vm), "clz32");
 }
 
 MacroAssemblerCodeRef sqrtThunkGenerator(VM* vm)
@@ -585,25 +625,15 @@ MacroAssemblerCodeRef sqrtThunkGenerator(VM* vm)
     jit.loadDoubleArgument(0, SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::regT0);
     jit.sqrtDouble(SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::fpRegT0);
     jit.returnDouble(SpecializedThunkJIT::fpRegT0);
-    return jit.finalize(vm->jitStubs->ctiNativeCall(vm), "sqrt");
+    return jit.finalize(vm->jitStubs->ctiNativeTailCall(vm), "sqrt");
 }
 
 
 #define UnaryDoubleOpWrapper(function) function##Wrapper
 enum MathThunkCallingConvention { };
 typedef MathThunkCallingConvention(*MathThunk)(MathThunkCallingConvention);
-extern "C" {
-
-double jsRound(double) REFERENCED_FROM_ASM;
-double jsRound(double d)
-{
-    double integer = ceil(d);
-    return integer - (integer - d > 0.5);
-}
-
-}
 
-#if CPU(X86_64) && COMPILER(GCC) && (OS(DARWIN) || OS(LINUX))
+#if CPU(X86_64) && COMPILER(GCC_OR_CLANG) && (OS(DARWIN) || OS(LINUX))
 
 #define defineUnaryDoubleOpWrapper(function) \
     asm( \
@@ -611,7 +641,9 @@ double jsRound(double d)
         ".globl " SYMBOL_STRING(function##Thunk) "\n" \
         HIDE_SYMBOL(function##Thunk) "\n" \
         SYMBOL_STRING(function##Thunk) ":" "\n" \
+        "pushq %rax\n" \
         "call " GLOBAL_REFERENCE(function) "\n" \
+        "popq %rcx\n" \
         "ret\n" \
     );\
     extern "C" { \
@@ -619,7 +651,7 @@ double jsRound(double d)
     } \
     static MathThunk UnaryDoubleOpWrapper(function) = &function##Thunk;
 
-#elif CPU(X86) && COMPILER(GCC) && OS(LINUX) && defined(__PIC__)
+#elif CPU(X86) && COMPILER(GCC_OR_CLANG) && OS(LINUX) && defined(__PIC__)
 #define defineUnaryDoubleOpWrapper(function) \
     asm( \
         ".text\n" \
@@ -643,19 +675,19 @@ double jsRound(double d)
     } \
     static MathThunk UnaryDoubleOpWrapper(function) = &function##Thunk;
 
-#elif CPU(X86) && COMPILER(GCC) && (OS(DARWIN) || OS(LINUX))
+#elif CPU(X86) && COMPILER(GCC_OR_CLANG) && (OS(DARWIN) || OS(LINUX))
 #define defineUnaryDoubleOpWrapper(function) \
     asm( \
         ".text\n" \
         ".globl " SYMBOL_STRING(function##Thunk) "\n" \
         HIDE_SYMBOL(function##Thunk) "\n" \
         SYMBOL_STRING(function##Thunk) ":" "\n" \
-        "subl $8, %esp\n" \
+        "subl $20, %esp\n" \
         "movsd %xmm0, (%esp) \n" \
         "call " GLOBAL_REFERENCE(function) "\n" \
         "fstpl (%esp) \n" \
         "movsd (%esp), %xmm0 \n" \
-        "addl $8, %esp\n" \
+        "addl $20, %esp\n" \
         "ret\n" \
     );\
     extern "C" { \
@@ -663,7 +695,7 @@ double jsRound(double d)
     } \
     static MathThunk UnaryDoubleOpWrapper(function) = &function##Thunk;
 
-#elif CPU(ARM_THUMB2) && COMPILER(GCC) && PLATFORM(IOS)
+#elif CPU(ARM_THUMB2) && COMPILER(GCC_OR_CLANG) && PLATFORM(IOS)
 
 #define defineUnaryDoubleOpWrapper(function) \
     asm( \
@@ -696,12 +728,38 @@ double jsRound(double d)
         HIDE_SYMBOL(function##Thunk) "\n" \
         SYMBOL_STRING(function##Thunk) ":" "\n" \
         "b " GLOBAL_REFERENCE(function) "\n" \
+        ".previous" \
     ); \
     extern "C" { \
         MathThunkCallingConvention function##Thunk(MathThunkCallingConvention); \
     } \
     static MathThunk UnaryDoubleOpWrapper(function) = &function##Thunk;
 
+#elif CPU(X86) && COMPILER(MSVC) && OS(WINDOWS)
+
+// MSVC does not accept floor, etc, to be called directly from inline assembly, so we need to wrap these functions.
+static double (_cdecl *floorFunction)(double) = floor;
+static double (_cdecl *ceilFunction)(double) = ceil;
+static double (_cdecl *expFunction)(double) = exp;
+static double (_cdecl *logFunction)(double) = log;
+static double (_cdecl *jsRoundFunction)(double) = jsRound;
+
+#define defineUnaryDoubleOpWrapper(function) \
+    extern "C" __declspec(naked) MathThunkCallingConvention function##Thunk(MathThunkCallingConvention) \
+    { \
+        __asm \
+        { \
+        __asm sub esp, 20 \
+        __asm movsd mmword ptr [esp], xmm0  \
+        __asm call function##Function \
+        __asm fstp qword ptr [esp] \
+        __asm movsd xmm0, mmword ptr [esp] \
+        __asm add esp, 20 \
+        __asm ret \
+        } \
+    } \
+    static MathThunk UnaryDoubleOpWrapper(function) = &function##Thunk;
+
 #else
 
 #define defineUnaryDoubleOpWrapper(function) \
@@ -716,7 +774,6 @@ defineUnaryDoubleOpWrapper(ceil);
 
 static const double oneConstant = 1.0;
 static const double negativeHalfConstant = -0.5;
-static const double zeroConstant = 0.0;
 static const double halfConstant = 0.5;
     
 MacroAssemblerCodeRef floorThunkGenerator(VM* vm)
@@ -740,7 +797,7 @@ MacroAssemblerCodeRef floorThunkGenerator(VM* vm)
     SpecializedThunkJIT::Jump intResult;
     SpecializedThunkJIT::JumpList doubleResult;
     if (jit.supportsFloatingPointTruncate()) {
-        jit.loadDouble(&zeroConstant, SpecializedThunkJIT::fpRegT1);
+        jit.moveZeroToDouble(SpecializedThunkJIT::fpRegT1);
         doubleResult.append(jit.branchDouble(MacroAssembler::DoubleEqual, SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::fpRegT1));
         SpecializedThunkJIT::JumpList slowPath;
         // Handle the negative doubles in the slow path for now.
@@ -757,7 +814,7 @@ MacroAssemblerCodeRef floorThunkGenerator(VM* vm)
     doubleResult.link(&jit);
     jit.returnDouble(SpecializedThunkJIT::fpRegT0);
 #endif // CPU(ARM64)
-    return jit.finalize(vm->jitStubs->ctiNativeCall(vm), "floor");
+    return jit.finalize(vm->jitStubs->ctiNativeTailCall(vm), "floor");
 }
 
 MacroAssemblerCodeRef ceilThunkGenerator(VM* vm)
@@ -770,17 +827,17 @@ MacroAssemblerCodeRef ceilThunkGenerator(VM* vm)
     jit.returnInt32(SpecializedThunkJIT::regT0);
     nonIntJump.link(&jit);
     jit.loadDoubleArgument(0, SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::regT0);
-#if CPU(ARM64)
-    jit.ceilDouble(SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::fpRegT0);
-#else
-    jit.callDoubleToDoublePreservingReturn(UnaryDoubleOpWrapper(ceil));
-#endif // CPU(ARM64)
+    if (jit.supportsFloatingPointRounding())
+        jit.ceilDouble(SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::fpRegT0);
+    else
+        jit.callDoubleToDoublePreservingReturn(UnaryDoubleOpWrapper(ceil));
+
     SpecializedThunkJIT::JumpList doubleResult;
     jit.branchConvertDoubleToInt32(SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::regT0, doubleResult, SpecializedThunkJIT::fpRegT1);
     jit.returnInt32(SpecializedThunkJIT::regT0);
     doubleResult.link(&jit);
     jit.returnDouble(SpecializedThunkJIT::fpRegT0);
-    return jit.finalize(vm->jitStubs->ctiNativeCall(vm), "ceil");
+    return jit.finalize(vm->jitStubs->ctiNativeTailCall(vm), "ceil");
 }
 
 MacroAssemblerCodeRef roundThunkGenerator(VM* vm)
@@ -796,12 +853,12 @@ MacroAssemblerCodeRef roundThunkGenerator(VM* vm)
     SpecializedThunkJIT::Jump intResult;
     SpecializedThunkJIT::JumpList doubleResult;
     if (jit.supportsFloatingPointTruncate()) {
-        jit.loadDouble(&zeroConstant, SpecializedThunkJIT::fpRegT1);
+        jit.moveZeroToDouble(SpecializedThunkJIT::fpRegT1);
         doubleResult.append(jit.branchDouble(MacroAssembler::DoubleEqual, SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::fpRegT1));
         SpecializedThunkJIT::JumpList slowPath;
         // Handle the negative doubles in the slow path for now.
         slowPath.append(jit.branchDouble(MacroAssembler::DoubleLessThanOrUnordered, SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::fpRegT1));
-        jit.loadDouble(&halfConstant, SpecializedThunkJIT::fpRegT1);
+        jit.loadDouble(MacroAssembler::TrustedImmPtr(&halfConstant), SpecializedThunkJIT::fpRegT1);
         jit.addDouble(SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::fpRegT1);
         slowPath.append(jit.branchTruncateDoubleToInt32(SpecializedThunkJIT::fpRegT1, SpecializedThunkJIT::regT0));
         intResult = jit.jump();
@@ -814,7 +871,7 @@ MacroAssemblerCodeRef roundThunkGenerator(VM* vm)
     jit.returnInt32(SpecializedThunkJIT::regT0);
     doubleResult.link(&jit);
     jit.returnDouble(SpecializedThunkJIT::fpRegT0);
-    return jit.finalize(vm->jitStubs->ctiNativeCall(vm), "round");
+    return jit.finalize(vm->jitStubs->ctiNativeTailCall(vm), "round");
 }
 
 MacroAssemblerCodeRef expThunkGenerator(VM* vm)
@@ -827,7 +884,7 @@ MacroAssemblerCodeRef expThunkGenerator(VM* vm)
     jit.loadDoubleArgument(0, SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::regT0);
     jit.callDoubleToDoublePreservingReturn(UnaryDoubleOpWrapper(exp));
     jit.returnDouble(SpecializedThunkJIT::fpRegT0);
-    return jit.finalize(vm->jitStubs->ctiNativeCall(vm), "exp");
+    return jit.finalize(vm->jitStubs->ctiNativeTailCall(vm), "exp");
 }
 
 MacroAssemblerCodeRef logThunkGenerator(VM* vm)
@@ -840,7 +897,7 @@ MacroAssemblerCodeRef logThunkGenerator(VM* vm)
     jit.loadDoubleArgument(0, SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::regT0);
     jit.callDoubleToDoublePreservingReturn(UnaryDoubleOpWrapper(log));
     jit.returnDouble(SpecializedThunkJIT::fpRegT0);
-    return jit.finalize(vm->jitStubs->ctiNativeCall(vm), "log");
+    return jit.finalize(vm->jitStubs->ctiNativeTailCall(vm), "log");
 }
 
 MacroAssemblerCodeRef absThunkGenerator(VM* vm)
@@ -853,14 +910,14 @@ MacroAssemblerCodeRef absThunkGenerator(VM* vm)
     jit.rshift32(SpecializedThunkJIT::regT0, MacroAssembler::TrustedImm32(31), SpecializedThunkJIT::regT1);
     jit.add32(SpecializedThunkJIT::regT1, SpecializedThunkJIT::regT0);
     jit.xor32(SpecializedThunkJIT::regT1, SpecializedThunkJIT::regT0);
-    jit.appendFailure(jit.branch32(MacroAssembler::Equal, SpecializedThunkJIT::regT0, MacroAssembler::TrustedImm32(1 << 31)));
+    jit.appendFailure(jit.branchTest32(MacroAssembler::Signed, SpecializedThunkJIT::regT0));
     jit.returnInt32(SpecializedThunkJIT::regT0);
     nonIntJump.link(&jit);
     // Shame about the double int conversion here.
     jit.loadDoubleArgument(0, SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::regT0);
     jit.absDouble(SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::fpRegT1);
     jit.returnDouble(SpecializedThunkJIT::fpRegT1);
-    return jit.finalize(vm->jitStubs->ctiNativeCall(vm), "abs");
+    return jit.finalize(vm->jitStubs->ctiNativeTailCall(vm), "abs");
 }
 
 MacroAssemblerCodeRef powThunkGenerator(VM* vm)
@@ -869,7 +926,7 @@ MacroAssemblerCodeRef powThunkGenerator(VM* vm)
     if (!jit.supportsFloatingPoint())
         return MacroAssemblerCodeRef::createSelfManagedCodeRef(vm->jitStubs->ctiNativeCall(vm));
 
-    jit.loadDouble(&oneConstant, SpecializedThunkJIT::fpRegT1);
+    jit.loadDouble(MacroAssembler::TrustedImmPtr(&oneConstant), SpecializedThunkJIT::fpRegT1);
     jit.loadDoubleArgument(0, SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::regT0);
     MacroAssembler::Jump nonIntExponent;
     jit.loadInt32Argument(1, SpecializedThunkJIT::regT0, nonIntExponent);
@@ -897,7 +954,7 @@ MacroAssemblerCodeRef powThunkGenerator(VM* vm)
 
     if (jit.supportsFloatingPointSqrt()) {
         nonIntExponent.link(&jit);
-        jit.loadDouble(&negativeHalfConstant, SpecializedThunkJIT::fpRegT3);
+        jit.loadDouble(MacroAssembler::TrustedImmPtr(&negativeHalfConstant), SpecializedThunkJIT::fpRegT3);
         jit.loadDoubleArgument(1, SpecializedThunkJIT::fpRegT2, SpecializedThunkJIT::regT0);
         jit.appendFailure(jit.branchDouble(MacroAssembler::DoubleLessThanOrEqual, SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::fpRegT1));
         jit.appendFailure(jit.branchDouble(MacroAssembler::DoubleNotEqualOrUnordered, SpecializedThunkJIT::fpRegT2, SpecializedThunkJIT::fpRegT3));
@@ -912,7 +969,7 @@ MacroAssemblerCodeRef powThunkGenerator(VM* vm)
     } else
         jit.appendFailure(nonIntExponent);
 
-    return jit.finalize(vm->jitStubs->ctiNativeCall(vm), "pow");
+    return jit.finalize(vm->jitStubs->ctiNativeTailCall(vm), "pow");
 }
 
 MacroAssemblerCodeRef imulThunkGenerator(VM* vm)
@@ -931,8 +988,7 @@ MacroAssemblerCodeRef imulThunkGenerator(VM* vm)
         nonIntArg0Jump.link(&jit);
         jit.loadDoubleArgument(0, SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::regT0);
         jit.branchTruncateDoubleToInt32(SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::regT0, SpecializedThunkJIT::BranchIfTruncateSuccessful).linkTo(doneLoadingArg0, &jit);
-        jit.xor32(SpecializedThunkJIT::regT0, SpecializedThunkJIT::regT0);
-        jit.jump(doneLoadingArg0);
+        jit.appendFailure(jit.jump());
     } else
         jit.appendFailure(nonIntArg0Jump);
 
@@ -940,117 +996,29 @@ MacroAssemblerCodeRef imulThunkGenerator(VM* vm)
         nonIntArg1Jump.link(&jit);
         jit.loadDoubleArgument(1, SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::regT1);
         jit.branchTruncateDoubleToInt32(SpecializedThunkJIT::fpRegT0, SpecializedThunkJIT::regT1, SpecializedThunkJIT::BranchIfTruncateSuccessful).linkTo(doneLoadingArg1, &jit);
-        jit.xor32(SpecializedThunkJIT::regT1, SpecializedThunkJIT::regT1);
-        jit.jump(doneLoadingArg1);
+        jit.appendFailure(jit.jump());
     } else
         jit.appendFailure(nonIntArg1Jump);
 
-    return jit.finalize(vm->jitStubs->ctiNativeCall(vm), "imul");
+    return jit.finalize(vm->jitStubs->ctiNativeTailCall(vm), "imul");
 }
 
-static MacroAssemblerCodeRef arrayIteratorNextThunkGenerator(VM* vm, ArrayIterationKind kind)
+MacroAssemblerCodeRef randomThunkGenerator(VM* vm)
 {
-    typedef SpecializedThunkJIT::TrustedImm32 TrustedImm32;
-    typedef SpecializedThunkJIT::TrustedImmPtr TrustedImmPtr;
-    typedef SpecializedThunkJIT::Address Address;
-    typedef SpecializedThunkJIT::BaseIndex BaseIndex;
-    typedef SpecializedThunkJIT::Jump Jump;
-    
-    SpecializedThunkJIT jit(vm);
-    // Make sure we're being called on an array iterator, and load m_iteratedObject, and m_nextIndex into regT0 and regT1 respectively
-    jit.loadArgumentWithSpecificClass(JSArrayIterator::info(), SpecializedThunkJIT::ThisArgument, SpecializedThunkJIT::regT4, SpecializedThunkJIT::regT1);
-
-    // Early exit if we don't have a thunk for this form of iteration
-    jit.appendFailure(jit.branch32(SpecializedThunkJIT::AboveOrEqual, Address(SpecializedThunkJIT::regT4, JSArrayIterator::offsetOfIterationKind()), TrustedImm32(ArrayIterateKeyValue)));
-    
-    jit.loadPtr(Address(SpecializedThunkJIT::regT4, JSArrayIterator::offsetOfIteratedObject()), SpecializedThunkJIT::regT0);
-    
-    jit.load32(Address(SpecializedThunkJIT::regT4, JSArrayIterator::offsetOfNextIndex()), SpecializedThunkJIT::regT1);
-    
-    // Pull out the butterfly from iteratedObject
-    jit.loadPtr(Address(SpecializedThunkJIT::regT0, JSCell::structureOffset()), SpecializedThunkJIT::regT2);
-    
-    jit.load8(Address(SpecializedThunkJIT::regT2, Structure::indexingTypeOffset()), SpecializedThunkJIT::regT3);
-    jit.loadPtr(Address(SpecializedThunkJIT::regT0, JSObject::butterflyOffset()), SpecializedThunkJIT::regT2);
-    Jump nullButterfly = jit.branchTestPtr(SpecializedThunkJIT::Zero, SpecializedThunkJIT::regT2);
-    
-    Jump notDone = jit.branch32(SpecializedThunkJIT::Below, SpecializedThunkJIT::regT1, Address(SpecializedThunkJIT::regT2, Butterfly::offsetOfPublicLength()));
-
-    nullButterfly.link(&jit);
+    SpecializedThunkJIT jit(vm, 0);
+    if (!jit.supportsFloatingPoint())
+        return MacroAssemblerCodeRef::createSelfManagedCodeRef(vm->jitStubs->ctiNativeCall(vm));
 
-    // Return the termination signal to indicate that we've finished
-    jit.move(TrustedImmPtr(vm->iterationTerminator.get()), SpecializedThunkJIT::regT0);
-    jit.returnJSCell(SpecializedThunkJIT::regT0);
-    
-    notDone.link(&jit);
-    
-    if (kind == ArrayIterateKey) {
-        jit.add32(TrustedImm32(1), Address(SpecializedThunkJIT::regT4, JSArrayIterator::offsetOfNextIndex()));
-        jit.returnInt32(SpecializedThunkJIT::regT1);
-        return jit.finalize(vm->jitStubs->ctiNativeCall(vm), "array-iterator-next-key");
-        
-    }
-    ASSERT(kind == ArrayIterateValue);
-    
-    // Okay, now we're returning a value so make sure we're inside the vector size
-    jit.appendFailure(jit.branch32(SpecializedThunkJIT::AboveOrEqual, SpecializedThunkJIT::regT1, Address(SpecializedThunkJIT::regT2, Butterfly::offsetOfVectorLength())));
-    
-    // So now we perform inline loads for int32, value/undecided, and double storage
-    Jump undecidedStorage = jit.branch32(SpecializedThunkJIT::Equal, SpecializedThunkJIT::regT3, TrustedImm32(ArrayWithUndecided));
-    Jump notContiguousStorage = jit.branch32(SpecializedThunkJIT::NotEqual, SpecializedThunkJIT::regT3, TrustedImm32(ArrayWithContiguous));
-    
-    undecidedStorage.link(&jit);
-    
-    jit.loadPtr(Address(SpecializedThunkJIT::regT0, JSObject::butterflyOffset()), SpecializedThunkJIT::regT2);
-    
 #if USE(JSVALUE64)
-    jit.load64(BaseIndex(SpecializedThunkJIT::regT2, SpecializedThunkJIT::regT1, SpecializedThunkJIT::TimesEight), SpecializedThunkJIT::regT0);
-    Jump notHole = jit.branchTest64(SpecializedThunkJIT::NonZero, SpecializedThunkJIT::regT0);
-    jit.move(JSInterfaceJIT::TrustedImm64(ValueUndefined), JSInterfaceJIT::regT0);
-    notHole.link(&jit);
-    jit.addPtr(TrustedImm32(1), Address(SpecializedThunkJIT::regT4, JSArrayIterator::offsetOfNextIndex()));
-    jit.returnJSValue(SpecializedThunkJIT::regT0);
-#else
-    jit.load32(BaseIndex(SpecializedThunkJIT::regT2, SpecializedThunkJIT::regT1, SpecializedThunkJIT::TimesEight, JSValue::offsetOfTag()), SpecializedThunkJIT::regT3);
-    Jump notHole = jit.branch32(SpecializedThunkJIT::NotEqual, SpecializedThunkJIT::regT3, TrustedImm32(JSValue::EmptyValueTag));
-    jit.move(JSInterfaceJIT::TrustedImm32(JSValue::UndefinedTag), JSInterfaceJIT::regT1);
-    jit.move(JSInterfaceJIT::TrustedImm32(0), JSInterfaceJIT::regT0);
-    jit.add32(TrustedImm32(1), Address(SpecializedThunkJIT::regT4, JSArrayIterator::offsetOfNextIndex()));
-    jit.returnJSValue(SpecializedThunkJIT::regT0, JSInterfaceJIT::regT1);
-    notHole.link(&jit);
-    jit.load32(BaseIndex(SpecializedThunkJIT::regT2, SpecializedThunkJIT::regT1, SpecializedThunkJIT::TimesEight, JSValue::offsetOfPayload()), SpecializedThunkJIT::regT0);
-    jit.add32(TrustedImm32(1), Address(SpecializedThunkJIT::regT4, JSArrayIterator::offsetOfNextIndex()));
-    jit.move(SpecializedThunkJIT::regT3, SpecializedThunkJIT::regT1);
-    jit.returnJSValue(SpecializedThunkJIT::regT0, SpecializedThunkJIT::regT1);
-#endif
-    notContiguousStorage.link(&jit);
-    
-    Jump notInt32Storage = jit.branch32(SpecializedThunkJIT::NotEqual, SpecializedThunkJIT::regT3, TrustedImm32(ArrayWithInt32));
-    jit.loadPtr(Address(SpecializedThunkJIT::regT0, JSObject::butterflyOffset()), SpecializedThunkJIT::regT2);
-    jit.load32(BaseIndex(SpecializedThunkJIT::regT2, SpecializedThunkJIT::regT1, SpecializedThunkJIT::TimesEight, JSValue::offsetOfPayload()), SpecializedThunkJIT::regT0);
-    jit.add32(TrustedImm32(1), Address(SpecializedThunkJIT::regT4, JSArrayIterator::offsetOfNextIndex()));
-    jit.returnInt32(SpecializedThunkJIT::regT0);
-    notInt32Storage.link(&jit);
-    
-    jit.appendFailure(jit.branch32(SpecializedThunkJIT::NotEqual, SpecializedThunkJIT::regT3, TrustedImm32(ArrayWithDouble)));
-    jit.loadPtr(Address(SpecializedThunkJIT::regT0, JSObject::butterflyOffset()), SpecializedThunkJIT::regT2);
-    jit.loadDouble(BaseIndex(SpecializedThunkJIT::regT2, SpecializedThunkJIT::regT1, SpecializedThunkJIT::TimesEight), SpecializedThunkJIT::fpRegT0);
-    jit.add32(TrustedImm32(1), Address(SpecializedThunkJIT::regT4, JSArrayIterator::offsetOfNextIndex()));
+    jit.emitRandomThunk(SpecializedThunkJIT::regT0, SpecializedThunkJIT::regT1, SpecializedThunkJIT::regT2, SpecializedThunkJIT::regT3, SpecializedThunkJIT::fpRegT0);
     jit.returnDouble(SpecializedThunkJIT::fpRegT0);
-    
-    return jit.finalize(vm->jitStubs->ctiNativeCall(vm), "array-iterator-next-value");
-}
 
-MacroAssemblerCodeRef arrayIteratorNextKeyThunkGenerator(VM* vm)
-{
-    return arrayIteratorNextThunkGenerator(vm, ArrayIterateKey);
+    return jit.finalize(vm->jitStubs->ctiNativeTailCall(vm), "random");
+#else
+    return MacroAssemblerCodeRef::createSelfManagedCodeRef(vm->jitStubs->ctiNativeCall(vm));
+#endif
 }
 
-MacroAssemblerCodeRef arrayIteratorNextValueThunkGenerator(VM* vm)
-{
-    return arrayIteratorNextThunkGenerator(vm, ArrayIterateValue);
-}
-    
 }
 
 #endif // ENABLE(JIT)