cmd/6g, cmd/8g, liblink: improve handling of float constants
* Enable basic constant propagation for floats.
The constant propagation is still not as aggressive as it could be.
* Implement MOVSS $(0), Xx and MOVSD $(0), Xx as XORPS Xx, Xx.
Sample code:
func f32() float32 {
var f float32
return f
}
func f64() float64 {
var f float64
return f
}
Before:
"".f32 t=1 size=32 value=0 args=0x8 locals=0x0
0x0000 00000 (demo.go:3) TEXT "".f32+0(SB),4,$0-8
0x0000 00000 (demo.go:3) FUNCDATA $0,gclocals·
a7a3692b8e27e823add69ec4239ba55f+0(SB)
0x0000 00000 (demo.go:3) FUNCDATA $1,gclocals·
3280bececceccd33cb74587feedb1f9f+0(SB)
0x0000 00000 (demo.go:3) MOVSS $f32.
00000000+0(SB),X0
0x0008 00008 (demo.go:4) MOVSS $f32.
00000000+0(SB),X0
0x0010 00016 (demo.go:5) MOVSS X0,"".~r0+8(FP)
0x0016 00022 (demo.go:5) RET ,
"".f64 t=1 size=32 value=0 args=0x8 locals=0x0
0x0000 00000 (demo.go:8) TEXT "".f64+0(SB),4,$0-8
0x0000 00000 (demo.go:8) FUNCDATA $0,gclocals·
a7a3692b8e27e823add69ec4239ba55f+0(SB)
0x0000 00000 (demo.go:8) FUNCDATA $1,gclocals·
3280bececceccd33cb74587feedb1f9f+0(SB)
0x0000 00000 (demo.go:8) MOVSD $f64.
0000000000000000+0(SB),X0
0x0008 00008 (demo.go:9) MOVSD $f64.
0000000000000000+0(SB),X0
0x0010 00016 (demo.go:10) MOVSD X0,"".~r0+8(FP)
0x0016 00022 (demo.go:10) RET ,
After:
"".f32 t=1 size=16 value=0 args=0x8 locals=0x0
0x0000 00000 (demo.go:3) TEXT "".f32+0(SB),4,$0-8
0x0000 00000 (demo.go:3) FUNCDATA $0,gclocals·
a7a3692b8e27e823add69ec4239ba55f+0(SB)
0x0000 00000 (demo.go:3) FUNCDATA $1,gclocals·
3280bececceccd33cb74587feedb1f9f+0(SB)
0x0000 00000 (demo.go:3) XORPS X0,X0
0x0003 00003 (demo.go:5) MOVSS X0,"".~r0+8(FP)
0x0009 00009 (demo.go:5) RET ,
"".f64 t=1 size=16 value=0 args=0x8 locals=0x0
0x0000 00000 (demo.go:8) TEXT "".f64+0(SB),4,$0-8
0x0000 00000 (demo.go:8) FUNCDATA $0,gclocals·
a7a3692b8e27e823add69ec4239ba55f+0(SB)
0x0000 00000 (demo.go:8) FUNCDATA $1,gclocals·
3280bececceccd33cb74587feedb1f9f+0(SB)
0x0000 00000 (demo.go:8) XORPS X0,X0
0x0003 00003 (demo.go:10) MOVSD X0,"".~r0+8(FP)
0x0009 00009 (demo.go:10) RET ,
Change-Id: Ie9eb65e324af4f664153d0a7cd22bb16b0fba16d
Reviewed-on: https://go-review.googlesource.com/2053
Reviewed-by: Russ Cox <rsc@golang.org>