cmd/compile,math: improve code generation for math.Abs
Implement int reg <-> fp reg moves on amd64.
If we see a load to int reg followed by an int->fp move, then we can just
load to the fp reg instead. Same for stores.
math.Abs is now:
MOVQ "".x+8(SP), AX
SHLQ $1, AX
SHRQ $1, AX
MOVQ AX, "".~r1+16(SP)
math.Copysign is now:
MOVQ "".x+8(SP), AX
SHLQ $1, AX
SHRQ $1, AX
MOVQ "".y+16(SP), CX
SHRQ $63, CX
SHLQ $63, CX
ORQ CX, AX
MOVQ AX, "".~r2+24(SP)
math.Float64bits is now:
MOVSD "".x+8(SP), X0
MOVSD X0, "".~r1+16(SP)
(it would be nicer to use a non-SSE reg for this, nothing is perfect)
And due to the fix for #21440, the inlined version of these improve as well.
name old time/op new time/op delta
Abs 1.38ns ± 5% 0.89ns ±10% -35.54% (p=0.000 n=10+10)
Copysign 1.56ns ± 7% 1.35ns ± 6% -13.77% (p=0.000 n=9+10)
Fixes #13095
Change-Id: Ibd7f2792412a6668608780b0688a77062e1f1499
Reviewed-on: https://go-review.googlesource.com/58732
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Ilya Tocar <ilya.tocar@intel.com>
diff --git a/src/math/abs.go b/src/math/abs.go
index 924ee7c..df83add 100644
--- a/src/math/abs.go
+++ b/src/math/abs.go
@@ -10,14 +10,5 @@
// Abs(±Inf) = +Inf
// Abs(NaN) = NaN
func Abs(x float64) float64 {
- // TODO: once golang.org/issue/13095 is fixed, change this to:
- // return Float64frombits(Float64bits(x) &^ (1 << 63))
- // But for now, this generates better code and can also be inlined:
- if x < 0 {
- return -x
- }
- if x == 0 {
- return 0 // return correctly abs(-0)
- }
- return x
+ return Float64frombits(Float64bits(x) &^ (1 << 63))
}
