| commit | eeaf508d13b463c0bd2224275e239c01e06f4ade | [log] [tgz] |
|---|---|---|
| author | David Chase <drchase@google.com> | Mon Dec 19 11:59:13 2022 -0500 |
| committer | Gopher Robot <gobot@golang.org> | Wed Dec 28 22:17:03 2022 +0000 |
| tree | 66677a33b3e19aee5300dfe5ca0c92b440238ef0 | |
| parent | 07b6ffb79c906a73573784e9fc71f98f1143d8fb [diff] |
[release-branch.go1.18] cmd/compile: sign-extend the 2nd argument of the LoweredAtomicCas32 on mips64x,riscv64
The function LoweredAtomicCas32 is implemented using the LL-SC instruction pair
on loong64, mips64x, riscv64. However,the LL instruction on loong64, mips64x,
riscv64 is sign-extended, so it is necessary to sign-extend the 2nd parameter
"old" of the LoweredAtomicCas32, so that the instruction BNE after LL can get
the desired result.
The function prototype of LoweredAtomicCas32 in golang:
func Cas32(ptr *uint32, old, new uint32) bool
When using an intrinsify implementation:
case 1: (*ptr) <= 0x80000000 && old < 0x80000000
E.g: (*ptr) = 0x7FFFFFFF, old = Rarg1= 0x7FFFFFFF
After run the instruction "LL (Rarg0), Rtmp": Rtmp = 0x7FFFFFFF
Rtmp ! = Rarg1(old) is false, the result we expect
case 2: (*ptr) >= 0x80000000 && old >= 0x80000000
E.g: (*ptr) = 0x80000000, old = Rarg1= 0x80000000
After run the instruction "LL (Rarg0), Rtmp": Rtmp = 0xFFFFFFFF_80000000
Rtmp ! = Rarg1(old) is true, which we do not expect
When using an non-intrinsify implementation:
Because Rarg1 is loaded from the stack using sign-extended instructions
ld.w, the situation described in Case 2 above does not occur
Benchmarks on linux/loong64:
name old time/op new time/op delta
Cas 50.0ns ± 0% 50.1ns ± 0% ~ (p=1.000 n=1+1)
Cas64 50.0ns ± 0% 50.1ns ± 0% ~ (p=1.000 n=1+1)
Cas-4 56.0ns ± 0% 56.0ns ± 0% ~ (p=1.000 n=1+1)
Cas64-4 56.0ns ± 0% 56.0ns ± 0% ~ (p=1.000 n=1+1)
Benchmarks on Loongson 3A4000 (GOARCH=mips64le, 1.8GHz)
name old time/op new time/op delta
Cas 70.4ns ± 0% 70.3ns ± 0% ~ (p=1.000 n=1+1)
Cas64 70.7ns ± 0% 70.6ns ± 0% ~ (p=1.000 n=1+1)
Cas-4 81.1ns ± 0% 80.8ns ± 0% ~ (p=1.000 n=1+1)
Cas64-4 80.9ns ± 0% 80.9ns ± 0% ~ (p=1.000 n=1+1)
Fixes #57344
Change-Id: I190a7fc648023b15fa392f7fdda5ac18c1561bac
Reviewed-on: https://go-review.googlesource.com/c/go/+/457135
Run-TryBot: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Wayne Zuo <wdvxdr@golangcn.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/458357
Run-TryBot: David Chase <drchase@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@google.com>
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