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cmd/compile: use MOVBQZX for OpAMD64LoweredHasCPUFeature

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In the commit message of CL 212360, I wrote:

> This new intrinsic ... generates MOVB+TESTB+NE.
> (It is possible that MOVBQZX+TESTQ+NE would be better.)

I should have tested. MOVBQZX+TESTQ+NE does in fact appear to be better.

For the benchmark in #36196, on my machine:

name      old time/op  new time/op  delta
FMA-8     0.86ns ± 6%  0.70ns ± 5%  -18.79%  (p=0.000 n=98+97)
NonFMA-8  0.61ns ± 5%  0.60ns ± 4%   -0.74%  (p=0.001 n=100+97)

Interestingly, these are both considerably faster than
the measurements I took a couple of months ago (1.4ns/2ns).
It appears that CL 219131 (clearing VZEROUPPER in asyncPreempt) helped a lot.
And FMA is now once again slower than NonFMA, although this change
helps it regain some ground.

Updates #15808
Updates #36351
Updates #36196

Change-Id: I8a326289a963b1939aaa7eaa2fab2ec536467c7d
Reviewed-on: https://go-review.googlesource.com/c/go/+/227238
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Josh Bleecher Snyder 2020-04-04 19:22:28 -07:00
parent 64f19d7080
commit 7ee8467b27
4 changed files with 22 additions and 5 deletions
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2
src/cmd/compile/internal/amd64/ssa.go
View File

@ -903,7 +903,7 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
p.From.Reg = v.Args[0].Reg()
gc.AddrAuto(&p.To, v)
case ssa.OpAMD64LoweredHasCPUFeature:
p := s.Prog(x86.AMOVB)
p := s.Prog(x86.AMOVBQZX)
p.From.Type = obj.TYPE_MEM
gc.AddAux(&p.From, v)
p.To.Type = obj.TYPE_REG

3
src/cmd/compile/internal/ssa/gen/AMD64.rules
View File

@ -478,7 +478,8 @@
(GetClosurePtr ...) -> (LoweredGetClosurePtr ...)
(GetCallerPC ...) -> (LoweredGetCallerPC ...)
(GetCallerSP ...) -> (LoweredGetCallerSP ...)
(HasCPUFeature ...) -> (LoweredHasCPUFeature ...)
(HasCPUFeature {s}) -> (SETNE (CMPQconst [0] (LoweredHasCPUFeature {s})))
(Addr ...) -> (LEAQ ...)
(LocalAddr {sym} base _) -> (LEAQ {sym} base)

2
src/cmd/compile/internal/ssa/gen/AMD64Ops.go
View File

@ -738,7 +738,7 @@ func init() {
// It saves all GP registers if necessary, but may clobber others.
{name: "LoweredWB", argLength: 3, reg: regInfo{inputs: []regMask{buildReg("DI"), buildReg("AX CX DX BX BP SI R8 R9")}, clobbers: callerSave &^ gp}, clobberFlags: true, aux: "Sym", symEffect: "None"},
{name: "LoweredHasCPUFeature", argLength: 0, reg: gp01, rematerializeable: true, typ: "bool", aux: "Sym", symEffect: "None"},
{name: "LoweredHasCPUFeature", argLength: 0, reg: gp01, rematerializeable: true, typ: "UInt64", aux: "Sym", symEffect: "None"},
// There are three of these functions so that they can have three different register inputs.
// When we check 0 <= c <= cap (A), then 0 <= b <= c (B), then 0 <= a <= b (C), we want the

20
src/cmd/compile/internal/ssa/rewriteAMD64.go
View File

@ -787,8 +787,7 @@ func rewriteValueAMD64(v *Value) bool {
case OpGreater64F:
return rewriteValueAMD64_OpGreater64F(v)
case OpHasCPUFeature:
v.Op = OpAMD64LoweredHasCPUFeature
return true
return rewriteValueAMD64_OpHasCPUFeature(v)
case OpHmul32:
v.Op = OpAMD64HMULL
return true
@ -29924,6 +29923,23 @@ func rewriteValueAMD64_OpGreater64F(v *Value) bool {
return true
}
}
func rewriteValueAMD64_OpHasCPUFeature(v *Value) bool {
b := v.Block
typ := &b.Func.Config.Types
// match: (HasCPUFeature {s})
// result: (SETNE (CMPQconst [0] (LoweredHasCPUFeature {s})))
for {
s := v.Aux
v.reset(OpAMD64SETNE)
v0 := b.NewValue0(v.Pos, OpAMD64CMPQconst, types.TypeFlags)
v0.AuxInt = 0
v1 := b.NewValue0(v.Pos, OpAMD64LoweredHasCPUFeature, typ.UInt64)
v1.Aux = s
v0.AddArg(v1)
v.AddArg(v0)
return true
}
}
func rewriteValueAMD64_OpIsInBounds(v *Value) bool {
v_1 := v.Args[1]
v_0 := v.Args[0]