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cmd/compile: reduce bits.Div64(0, lo, y) to 64 bit division

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With this change, these two functions generate identical code:

func f(x uint64) (uint64, uint64) {
	return bits.Div64(0, x, 5)
}

func g(x uint64) (uint64, uint64) {
	return x / 5, x % 5
}

Updates #31582

Change-Id: Ia96c2e67f8af5dd985823afee5f155608c04a4b6
Reviewed-on: https://go-review.googlesource.com/c/go/+/173197
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Josh Bleecher Snyder 2019-04-20 11:09:34 -07:00
parent d23cba683e
commit 68d4b1265e
3 changed files with 61 additions and 0 deletions
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2
src/cmd/compile/internal/ssa/gen/generic.rules
View File

@ -146,6 +146,8 @@
(Div64u (Const64 [c]) (Const64 [d])) && d != 0 -> (Const64 [int64(uint64(c)/uint64(d))])
(Div32F (Const32F [c]) (Const32F [d])) -> (Const32F [auxFrom32F(auxTo32F(c) / auxTo32F(d))])
(Div64F (Const64F [c]) (Const64F [d])) -> (Const64F [auxFrom64F(auxTo64F(c) / auxTo64F(d))])
(Select0 (Div128u (Const64 [0]) lo y)) -> (Div64u lo y)
(Select1 (Div128u (Const64 [0]) lo y)) -> (Mod64u lo y)
(Not (ConstBool [c])) -> (ConstBool [1-c])

54
src/cmd/compile/internal/ssa/rewritegeneric.go
View File

@ -389,6 +389,10 @@ func rewriteValuegeneric(v *Value) bool {
return rewriteValuegeneric_OpRsh8x64_0(v)
case OpRsh8x8:
return rewriteValuegeneric_OpRsh8x8_0(v)
case OpSelect0:
return rewriteValuegeneric_OpSelect0_0(v)
case OpSelect1:
return rewriteValuegeneric_OpSelect1_0(v)
case OpSignExt16to32:
return rewriteValuegeneric_OpSignExt16to32_0(v)
case OpSignExt16to64:
@ -26587,6 +26591,56 @@ func rewriteValuegeneric_OpRsh8x8_0(v *Value) bool {
}
return false
}
func rewriteValuegeneric_OpSelect0_0(v *Value) bool {
// match: (Select0 (Div128u (Const64 [0]) lo y))
// cond:
// result: (Div64u lo y)
for {
v_0 := v.Args[0]
if v_0.Op != OpDiv128u {
break
}
y := v_0.Args[2]
v_0_0 := v_0.Args[0]
if v_0_0.Op != OpConst64 {
break
}
if v_0_0.AuxInt != 0 {
break
}
lo := v_0.Args[1]
v.reset(OpDiv64u)
v.AddArg(lo)
v.AddArg(y)
return true
}
return false
}
func rewriteValuegeneric_OpSelect1_0(v *Value) bool {
// match: (Select1 (Div128u (Const64 [0]) lo y))
// cond:
// result: (Mod64u lo y)
for {
v_0 := v.Args[0]
if v_0.Op != OpDiv128u {
break
}
y := v_0.Args[2]
v_0_0 := v_0.Args[0]
if v_0_0.Op != OpConst64 {
break
}
if v_0_0.AuxInt != 0 {
break
}
lo := v_0.Args[1]
v.reset(OpMod64u)
v.AddArg(lo)
v.AddArg(y)
return true
}
return false
}
func rewriteValuegeneric_OpSignExt16to32_0(v *Value) bool {
// match: (SignExt16to32 (Const16 [c]))
// cond:

5
test/codegen/mathbits.go
View File

@ -538,3 +538,8 @@ func Div64(hi, lo, x uint64) (q, r uint64) {
// amd64:"DIVQ"
return bits.Div64(hi, lo, x)
}
func Div64degenerate(x uint64) (q, r uint64) {
// amd64:-"DIVQ"
return bits.Div64(0, x, 5)
}