delta/go-git.git/src/internal, branch dev.cmdgo

all: replace runtime SSE2 detection with GO386 setting

2021-08-23T21:22:58+00:00

When GO386=sse2 we can assume sse2 to be present without
a runtime check. If GO386=softfloat is set we can avoid
the usage of SSE2 even if detected.

This might cause a memcpy, memclr and bytealg slowdown of Go
binaries compiled with softfloat on machines that support
SSE2. Such setups are rare and should use GO386=sse2 instead
if performance matters.

On targets that support SSE2 we avoid the runtime overhead of
dynamic cpu feature dispatch.

The removal of runtime sse2 checks also allows to simplify
internal/cpu further by removing handling of the required
feature option as a followup after this CL.

Change-Id: I90a853a8853a405cb665497c6d1a86556947ba17
Reviewed-on: https://go-review.googlesource.com/c/go/+/344350
Trust: Martin Möhrmann 
Run-TryBot: Martin Möhrmann 
TryBot-Result: Go Bot 
Reviewed-by: Keith Randall

runtime: use RDTSCP for instruction stream serialized read of TSC

2021-08-23T20:32:04+00:00

To measure all instructions having been completed before reading
the time stamp counter with RDTSC an instruction sequence that
has instruction stream serializing properties which guarantee
waiting until all previous instructions have been executed is
needed. This does not necessary mean to wait for all stores to
be globally visible.

This CL aims to remove vendor specific logic for determining the
instruction sequence with CPU feature flag checks that are
CPU vendor independent.

For intel LFENCE has the wanted properties at least
since it was introduced together with SSE2 support.

On AMD instruction stream serializing LFENCE is supported by setting
an MSR C001_1029[1]=1 on AMD family 10h/12h/14h/15h/16h/17h processors.
AMD family 0Fh/11h processors support LFENCE as serializing always.
AMD plans support for this MSR and access to this bit for all future processors.
Source: https://developer.amd.com/wp-content/resources/Managing-Speculation-on-AMD-Processors.pdf

Reading the MSR to determine LFENCE properties is not always possible
or reliable (hypervisors). The Linux kernel is relying on serializing
LFENCE on AMD CPUs since a commit in July 2019: https://lkml.org/lkml/2019/7/22/295
and the MSR C001_1029 to enable serialization has been set by default
with the Spectre v1 mitigations.

Using an MFENCE on AMD is waiting on previous instructions having been executed
but in addition also flushes store buffers.

To align the serialization properties without runtime detection
of CPU manufacturers we can use the newer RDTSCP instruction which
waits until all previous instructions have been executed.

RDTSCP is available on Intel since around 2008 and on AMD CPUs since
around 2006. Support for RDTSCP can be checked independently
of manufacturer by checking CPUID bits.

Using RDTSCP is the default in Linux to read TSC in program order
when the instruction is available.
https://github.com/torvalds/linux/blob/e22ce8eb631bdc47a4a4ea7ecf4e4ba499db4f93/arch/x86/include/asm/msr.h#L231

Change-Id: Ifa841843b9abb2816f8f0754a163ebf01385306d
Reviewed-on: https://go-review.googlesource.com/c/go/+/344429
Reviewed-by: Keith Randall
Trust: Martin Möhrmann
Run-TryBot: Martin Möhrmann
TryBot-Result: Go Bot

internal/buildcfg: change GOEXPERIMENT to always return non-empty string

2021-08-23T20:04:34+00:00

Rather than returning "", we now return "," (which is a no-op). This
ensures that the returned string always overrides DefaultGOEXPERIMENT.

This fixes a bootstrapping issue where GOROOT_BOOTSTRAP was built with
"GOEXPERIMENT=fieldtrack ./make.bash". cmd/dist sets GOEXPERIMENT=none
during bootstrapping, which was causing cmd/go to set GOEXPERIMENT=""
when executing cmd/compile; but then cmd/compile ignores the
environment variable (because it's empty) and instead uses
DefaultGOEXPERIMENT.

Fixes #47921.

Change-Id: I657ff6cdfb294a94f6a2f58c306ceed7f104416b
Reviewed-on: https://go-review.googlesource.com/c/go/+/344511
Run-TryBot: Matthew Dempsky 
TryBot-Result: Go Bot 
Trust: Matthew Dempsky 
Reviewed-by: Heschi Kreinick

crypto/rand, internal/syscall/unix: don't use getentropy on iOS

2021-08-20T16:44:10+00:00

CL 302489 switched crypto/rand to use getentropy on darwin, however this
function is not available on iOS. Enable getentropy only on macOS and
disable it on iOS.

Fixes #47812

Change-Id: Ib7ba5d77346aee87904bb93d60cacc845f5c0089
Reviewed-on: https://go-review.googlesource.com/c/go/+/343609
Trust: Tobias Klauser 
Run-TryBot: Tobias Klauser 
Reviewed-by: Brad Fitzpatrick 
Reviewed-by: Ian Lance Taylor 
TryBot-Result: Go Bot

net: reduce allocations for UDP send/recv on Windows

2021-08-16T23:57:10+00:00

This brings the optimizations added in CLs 331489 and 331490 to Windows.

Updates #43451

Change-Id: I75cf520050325d9eb5c2785d6d8677cc864fcac8
Reviewed-on: https://go-review.googlesource.com/c/go/+/331511
Trust: Josh Bleecher Snyder 
Run-TryBot: Josh Bleecher Snyder 
TryBot-Result: Go Bot 
Reviewed-by: Damien Neil

net: reduce allocation size in ReadFromUDP

2021-08-16T23:57:02+00:00

Switch to concrete types. Bring your own object to fill in.

Allocate just enough for the IP byte slice.
The allocation is now just 4 bytes for IPv4,
which puts it in the tiny allocator, which is much faster.

name                  old time/op    new time/op    delta
WriteToReadFromUDP-8    13.7µs ± 1%    13.4µs ± 2%   -2.49%  (p=0.000 n=10+10)

name                  old alloc/op   new alloc/op   delta
WriteToReadFromUDP-8     32.0B ± 0%      4.0B ± 0%  -87.50%  (p=0.000 n=10+10)

name                  old allocs/op  new allocs/op  delta
WriteToReadFromUDP-8      1.00 ± 0%      1.00 ± 0%     ~     (all equal)

Windows is temporarily stubbed out.

Updates #43451

Change-Id: Ief506f891b401d28715d22dce6ebda037941924e
Reviewed-on: https://go-review.googlesource.com/c/go/+/331490
Trust: Josh Bleecher Snyder 
Trust: Damien Neil 
Run-TryBot: Josh Bleecher Snyder 
Run-TryBot: Damien Neil 
Reviewed-by: Damien Neil

net: remove allocation from UDPConn.WriteTo

2021-08-16T23:54:32+00:00

Duplicate some code to avoid an interface.

name                  old time/op    new time/op    delta
WriteToReadFromUDP-8    6.38µs ±20%    5.59µs ±10%  -12.38%  (p=0.001 n=10+9)

name                  old alloc/op   new alloc/op   delta
WriteToReadFromUDP-8     64.0B ± 0%     32.0B ± 0%  -50.00%  (p=0.000 n=10+10)

name                  old allocs/op  new allocs/op  delta
WriteToReadFromUDP-8      2.00 ± 0%      1.00 ± 0%  -50.00%  (p=0.000 n=10+10)

Windows is temporarily stubbed out.

Updates #43451

Change-Id: Ied15ff92268c652cf445836e0446025eaeb60cc9
Reviewed-on: https://go-review.googlesource.com/c/go/+/331489
Trust: Josh Bleecher Snyder 
Trust: Damien Neil 
Run-TryBot: Josh Bleecher Snyder 
TryBot-Result: Go Bot 
Reviewed-by: Ian Lance Taylor 
Reviewed-by: Damien Neil

internal/syscall/unix: change Ioctl arg type to unsafe.Pointer on AIX

2021-08-16T16:58:24+00:00

Without this change, this code is technically in violation of the
unsafe.Pointer rules since the conversion from unsafe.Pointer to uintptr has
to happen when calling into the syscall6 assembly implementation.

Change-Id: I4821f5bf9788c8fa2efeb041f811ed092e07ae74
Reviewed-on: https://go-review.googlesource.com/c/go/+/340949
Trust: Matt Layher 
Run-TryBot: Ian Lance Taylor 
TryBot-Result: Go Bot 
Reviewed-by: Ian Lance Taylor

all: gofmt more (but vendor, testdata, and top-level test directories)

2021-08-13T20:45:17+00:00

CL 294430 made packages in std and cmd modules use Go 1.17 gofmt format,
adding //go:build lines. This change applies the same formatting to some
more packages that 'go fmt' missed (e.g., syscall/js, runtime/msan), and
everything else that is easy and safe to modify in bulk.

Consider the top-level test directory, testdata, and vendor directories
out of scope, since there are many files that don't follow strict gofmt
formatting, often for intentional and legitimate reasons (testing gofmt
itself, invalid Go programs that shouldn't crash the compiler, etc.).

That makes it easy and safe to gofmt -w the .go files that are found
with gofmt -l with aforementioned directories filtered out:

	$ gofmt -l . 2>/dev/null | \
		grep -v '^test/' | \
		grep -v '/testdata/' | \
		grep -v '/vendor/' | wc -l
	      51

None of the 51 files are generated. After this change, the same command
prints 0.

For #41184.

Change-Id: Ia96ee2a0f998d6a167d4473bcad17ad09bc1d86e
Reviewed-on: https://go-review.googlesource.com/c/go/+/341009
Run-TryBot: Dmitri Shuralyov 
TryBot-Result: Go Bot 
Reviewed-by: Ian Lance Taylor 
Trust: Dmitri Shuralyov

[dev.typeparams] runtime, internal/bytealg: remove regabi fallback code on AMD64

2021-08-11T17:08:54+00:00

As we commit to always enabling register ABI on AMD64, remove the
fallback code.

Change-Id: I30556858ba4bac367495fa94f6a8682ecd771196
Reviewed-on: https://go-review.googlesource.com/c/go/+/341152
Trust: Cherry Mui 
Run-TryBot: Cherry Mui 
TryBot-Result: Go Bot 
Reviewed-by: Michael Knyszek 
Reviewed-by: Austin Clements