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

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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
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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 {