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cmd/compile: rewrite 2*x+c into LEAx1 on amd64

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Rewrite x<<1+c into x+x+c, which can be expressed as a single LEAQ/LEAL.

Bit of a special case, but the single-instruction
LEA is both shorter and faster than SHL then ADD.

Triggers 293 times during make.bash.

Change-Id: I3f09c8e9a8f3859d1eeed336f095fc3ada79c2c1
Reviewed-on: https://go-review.googlesource.com/108938
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 2018-04-23 13:49:51 -07:00
parent c0769741f5
commit d292f77e95
3 changed files with 48 additions and 1 deletions
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1
src/cmd/compile/internal/ssa/gen/AMD64.rules
View File

@ -925,6 +925,7 @@
// combine ADDQ/ADDQconst into LEAQ1
(ADDQconst [c] (ADDQ x y)) -> (LEAQ1 [c] x y)
(ADDQ (ADDQconst [c] x) y) -> (LEAQ1 [c] x y)
(ADD(Q|L)const [c] (SHL(Q|L)const [1] x)) -> (LEA(Q|L)1 [c] x x)
// fold ADDQ into LEAQ
(ADDQconst [c] (LEAQ [d] {s} x)) && is32Bit(c+d) -> (LEAQ [c+d] {s} x)

43
src/cmd/compile/internal/ssa/rewriteAMD64.go
View File

@ -26,7 +26,7 @@ func rewriteValueAMD64(v *Value) bool {
case OpAMD64ADDQ:
return rewriteValueAMD64_OpAMD64ADDQ_0(v) || rewriteValueAMD64_OpAMD64ADDQ_10(v) || rewriteValueAMD64_OpAMD64ADDQ_20(v)
case OpAMD64ADDQconst:
return rewriteValueAMD64_OpAMD64ADDQconst_0(v)
return rewriteValueAMD64_OpAMD64ADDQconst_0(v) || rewriteValueAMD64_OpAMD64ADDQconst_10(v)
case OpAMD64ADDQconstmem:
return rewriteValueAMD64_OpAMD64ADDQconstmem_0(v)
case OpAMD64ADDQmem:
@ -1313,6 +1313,25 @@ func rewriteValueAMD64_OpAMD64ADDL_10(v *Value) bool {
return false
}
func rewriteValueAMD64_OpAMD64ADDLconst_0(v *Value) bool {
// match: (ADDLconst [c] (SHLLconst [1] x))
// cond:
// result: (LEAL1 [c] x x)
for {
c := v.AuxInt
v_0 := v.Args[0]
if v_0.Op != OpAMD64SHLLconst {
break
}
if v_0.AuxInt != 1 {
break
}
x := v_0.Args[0]
v.reset(OpAMD64LEAL1)
v.AuxInt = c
v.AddArg(x)
v.AddArg(x)
return true
}
// match: (ADDLconst [c] x)
// cond: int32(c)==0
// result: x
@ -2077,6 +2096,25 @@ func rewriteValueAMD64_OpAMD64ADDQconst_0(v *Value) bool {
v.AddArg(y)
return true
}
// match: (ADDQconst [c] (SHLQconst [1] x))
// cond:
// result: (LEAQ1 [c] x x)
for {
c := v.AuxInt
v_0 := v.Args[0]
if v_0.Op != OpAMD64SHLQconst {
break
}
if v_0.AuxInt != 1 {
break
}
x := v_0.Args[0]
v.reset(OpAMD64LEAQ1)
v.AuxInt = c
v.AddArg(x)
v.AddArg(x)
return true
}
// match: (ADDQconst [c] (LEAQ [d] {s} x))
// cond: is32Bit(c+d)
// result: (LEAQ [c+d] {s} x)
@ -2240,6 +2278,9 @@ func rewriteValueAMD64_OpAMD64ADDQconst_0(v *Value) bool {
v.AddArg(x)
return true
}
return false
}
func rewriteValueAMD64_OpAMD64ADDQconst_10(v *Value) bool {
// match: (ADDQconst [off] x:(SP))
// cond:
// result: (LEAQ [off] x)

5
test/codegen/arithmetic.go
View File

@ -173,3 +173,8 @@ func CapMod(a []int) int {
// amd64:"ANDQ\t[$]4095"
return cap(a) % ((1 << 11) + 2048)
}
func AddMul(x int) int {
// amd64:"LEAQ\t1"
return 2*x + 1
}