From 250b96a7bfa5b9ac0f31e70e768173f57a61d2f7 Mon Sep 17 00:00:00 2001
From: Josh Bleecher Snyder <josharian@gmail.com>
Date: Tue, 19 Mar 2019 12:26:22 -0700
Subject: [PATCH] cmd/compile: slightly optimize adding 128
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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'SUBQ $-0x80, r' is shorter to encode than 'ADDQ $0x80, r',
and functionally equivalent. Use it instead.
Shaves off a few bytes here and there:
file before after Δ %
compile 25935856 25927664 -8192 -0.032%
nm 4251840 4247744 -4096 -0.096%
Change-Id: Ia9e02ea38cbded6a52a613b92e3a914f878d931e
Reviewed-on: https://go-review.googlesource.com/c/go/+/168344
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
---
src/cmd/compile/internal/amd64/ssa.go | 20 +++++++++++++++++---
test/codegen/arithmetic.go | 10 ++++++++++
2 files changed, 27 insertions(+), 3 deletions(-)
diff --git a/src/cmd/compile/internal/amd64/ssa.go b/src/cmd/compile/internal/amd64/ssa.go
index 48b4f7d0b51..5b8590c357f 100644
--- a/src/cmd/compile/internal/amd64/ssa.go
+++ b/src/cmd/compile/internal/amd64/ssa.go
@@ -414,7 +414,8 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
r := v.Reg()
a := v.Args[0].Reg()
if r == a {
- if v.AuxInt == 1 {
+ switch v.AuxInt {
+ case 1:
var asm obj.As
// Software optimization manual recommends add $1,reg.
// But inc/dec is 1 byte smaller. ICC always uses inc
@@ -430,8 +431,7 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
p.To.Type = obj.TYPE_REG
p.To.Reg = r
return
- }
- if v.AuxInt == -1 {
+ case -1:
var asm obj.As
if v.Op == ssa.OpAMD64ADDQconst {
asm = x86.ADECQ
@@ -442,6 +442,20 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
p.To.Type = obj.TYPE_REG
p.To.Reg = r
return
+ case 0x80:
+ // 'SUBQ $-0x80, r' is shorter to encode than
+ // and functionally equivalent to 'ADDQ $0x80, r'.
+ asm := x86.ASUBL
+ if v.Op == ssa.OpAMD64ADDQconst {
+ asm = x86.ASUBQ
+ }
+ p := s.Prog(asm)
+ p.From.Type = obj.TYPE_CONST
+ p.From.Offset = -0x80
+ p.To.Type = obj.TYPE_REG
+ p.To.Reg = r
+ return
+
}
p := s.Prog(v.Op.Asm())
p.From.Type = obj.TYPE_CONST
diff --git a/test/codegen/arithmetic.go b/test/codegen/arithmetic.go
index 16d7d25d3e4..b5976be9d25 100644
--- a/test/codegen/arithmetic.go
+++ b/test/codegen/arithmetic.go
@@ -381,3 +381,13 @@ func MULS(a, b, c uint32) (uint32, uint32, uint32) {
r2 := c - b*64
return r0, r1, r2
}
+
+func addSpecial(a, b, c uint32) (uint32, uint32, uint32) {
+ // amd64:`INCL`
+ a++
+ // amd64:`DECL`
+ b--
+ // amd64:`SUBL.*-128`
+ c += 128
+ return a, b, c
+}
--
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