mirror
/
go
mirror of https://github.com/golang/go.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

cmd/compile/internal/ssa: don't spill register offsets on amd64 

Transform (ADDQconst SP) into (LEA SP), because lea is rematerializeable,
so this avoids register spill. We can't mark ADDQconst as rematerializeable,
because it clobbers flags. This makes go binary ~2kb smaller.

For reference here is generated code for function from bug report.
Before:
        CALL    "".g(SB)
        MOVBLZX (SP), AX
        LEAQ    8(SP), DI
        TESTB   AX, AX
        JEQ     15
        MOVQ    "".p(SP), SI
        DUFFCOPY        $196
        MOVQ    $0, (SP)
        PCDATA  $0, $1
        CALL    "".h(SB)
        RET
        MOVQ    DI, ""..autotmp_2-8(SP) // extra spill
        PCDATA  $0, $2
        CALL    "".g(SB)
        MOVQ    ""..autotmp_2-8(SP), DI // extra register fill
        MOVQ    "".p(SP), SI
        DUFFCOPY        $196
        MOVQ    $1, (SP)
        PCDATA  $0, $1
        CALL    "".h(SB)
        JMP     14
        END

After:
        CALL    "".g(SB)
        MOVBLZX (SP), AX
        TESTB   AX, AX
        JEQ     15
        LEAQ    8(SP), DI
        MOVQ    "".p(SP), SI
        DUFFCOPY        $196
        MOVQ    $0, (SP)
        PCDATA  $0, $1
        CALL    "".h(SB)
        RET
        PCDATA  $0, $0  // no spill
        CALL    "".g(SB)
        LEAQ    8(SP), DI // rematerialized instead
        MOVQ    "".p(SP), SI
        DUFFCOPY        $196
        MOVQ    $1, (SP)
        PCDATA  $0, $1
        CALL    "".h(SB)
        JMP     14
        END

Fixes #22947

Change-Id: I8f33b860dc6c8828373477171b172ca2ce30074f
Reviewed-on: https://go-review.googlesource.com/81815
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Ilya Tocar 2017-12-04 14:24:16 -06:00
parent de4edf3de7
commit 9916feeddf
2 changed files with 18 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
src/cmd/compile/internal/ssa/gen/AMD64.rules
View File

@ -2662,3 +2662,7 @@
(MOVLf2i <t> (Arg [off] {sym})) -> @b.Func.Entry (Arg <t> [off] {sym})
(MOVQi2f <t> (Arg [off] {sym})) -> @b.Func.Entry (Arg <t> [off] {sym})
(MOVLi2f <t> (Arg [off] {sym})) -> @b.Func.Entry (Arg <t> [off] {sym})
// LEAQ is rematerializeable, so this helps to avoid register spill.
// See isuue 22947 for details
(ADDQconst [off] x:(SP)) -> (LEAQ [off] x)

14
src/cmd/compile/internal/ssa/rewriteAMD64.go
View File

@ -2054,6 +2054,20 @@ func rewriteValueAMD64_OpAMD64ADDQconst_0(v *Value) bool {
v.AddArg(x)
return true
}
// match: (ADDQconst [off] x:(SP))
// cond:
// result: (LEAQ [off] x)
for {
off := v.AuxInt
x := v.Args[0]
if x.Op != OpSP {
break
}
v.reset(OpAMD64LEAQ)
v.AuxInt = off
v.AddArg(x)
return true
}
return false
}
func rewriteValueAMD64_OpAMD64ADDQconstmem_0(v *Value) bool {