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[dev.ssa] cmd/compile/internal/ssa: distribute multiplication into addition

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* This is a very basic form of straight line strength reduction.
* Removes one multiplication from a[b].c++; a[b+1].c++
* It increases pressure on the register allocator because
CSE creates more copies of the multiplication sizeof(a[0])*b.

Change-Id: I686a18e9c24cc6f8bdfa925713afed034f7d36d0
Reviewed-on: https://go-review.googlesource.com/20091
Run-TryBot: Alexandru Moșoi <alexandru@mosoi.ro>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Alexandru Moșoi 2016-03-01 13:39:47 +01:00 committed by Alexandru Moșoi
parent e96b232993
commit 1f6e9e36b0
2 changed files with 75 additions and 0 deletions
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5
src/cmd/compile/internal/ssa/gen/generic.rules
View File

@ -147,6 +147,11 @@
(Xor16 x (Const16 <t> [c])) && x.Op != OpConst16 -> (Xor16 (Const16 <t> [c]) x)
(Xor8 x (Const8 <t> [c])) && x.Op != OpConst8 -> (Xor8 (Const8 <t> [c]) x)
// Distribute multiplication c * (d+x) -> c*d + c*x. Useful for:
// a[i].b = ...; a[i+1].b = ...
(Mul64 (Const64 <t> [c]) (Add64 <t> (Const64 <t> [d]) x)) -> (Add64 (Const64 <t> [c*d]) (Mul64 <t> (Const64 <t> [c]) x))
(Mul32 (Const32 <t> [c]) (Add32 <t> (Const32 <t> [d]) x)) -> (Add32 (Const32 <t> [c*d]) (Mul32 <t> (Const32 <t> [c]) x))
// rewrite shifts of 8/16/32 bit consts into 64 bit consts to reduce
// the number of the other rewrite rules for const shifts
(Lsh64x32 <t> x (Const32 [c])) -> (Lsh64x64 x (Const64 <t> [int64(uint32(c))]))

70
src/cmd/compile/internal/ssa/rewritegeneric.go
View File

@ -4044,6 +4044,41 @@ func rewriteValuegeneric_OpMul32(v *Value, config *Config) bool {
v.AddArg(x)
return true
}
// match: (Mul32 (Const32 <t> [c]) (Add32 <t> (Const32 <t> [d]) x))
// cond:
// result: (Add32 (Const32 <t> [c*d]) (Mul32 <t> (Const32 <t> [c]) x))
for {
if v.Args[0].Op != OpConst32 {
break
}
t := v.Args[0].Type
c := v.Args[0].AuxInt
if v.Args[1].Op != OpAdd32 {
break
}
if v.Args[1].Type != v.Args[0].Type {
break
}
if v.Args[1].Args[0].Op != OpConst32 {
break
}
if v.Args[1].Args[0].Type != v.Args[0].Type {
break
}
d := v.Args[1].Args[0].AuxInt
x := v.Args[1].Args[1]
v.reset(OpAdd32)
v0 := b.NewValue0(v.Line, OpConst32, t)
v0.AuxInt = c * d
v.AddArg(v0)
v1 := b.NewValue0(v.Line, OpMul32, t)
v2 := b.NewValue0(v.Line, OpConst32, t)
v2.AuxInt = c
v1.AddArg(v2)
v1.AddArg(x)
v.AddArg(v1)
return true
}
// match: (Mul32 (Const32 [0]) _)
// cond:
// result: (Const32 [0])
@ -4099,6 +4134,41 @@ func rewriteValuegeneric_OpMul64(v *Value, config *Config) bool {
v.AddArg(x)
return true
}
// match: (Mul64 (Const64 <t> [c]) (Add64 <t> (Const64 <t> [d]) x))
// cond:
// result: (Add64 (Const64 <t> [c*d]) (Mul64 <t> (Const64 <t> [c]) x))
for {
if v.Args[0].Op != OpConst64 {
break
}
t := v.Args[0].Type
c := v.Args[0].AuxInt
if v.Args[1].Op != OpAdd64 {
break
}
if v.Args[1].Type != v.Args[0].Type {
break
}
if v.Args[1].Args[0].Op != OpConst64 {
break
}
if v.Args[1].Args[0].Type != v.Args[0].Type {
break
}
d := v.Args[1].Args[0].AuxInt
x := v.Args[1].Args[1]
v.reset(OpAdd64)
v0 := b.NewValue0(v.Line, OpConst64, t)
v0.AuxInt = c * d
v.AddArg(v0)
v1 := b.NewValue0(v.Line, OpMul64, t)
v2 := b.NewValue0(v.Line, OpConst64, t)
v2.AuxInt = c
v1.AddArg(v2)
v1.AddArg(x)
v.AddArg(v1)
return true
}
// match: (Mul64 (Const64 [0]) _)
// cond:
// result: (Const64 [0])