e85265e8c2
This CL teaches SSA to recognize code of the form
// b is a boolean value, i is an int of some flavor
if b {
i = 1
} else {
i = 0
}
and use b's underlying 0/1 representation for i
instead of generating jumps.
Unfortunately, it does not work on the obvious code:
func bool2int(b bool) int {
if b {
return 1
}
return 0
}
This is left for future work.
Note that the existing phiopt optimizations also don't work for:
func neg(b bool) bool {
if b {
return false
}
return true
}
In the meantime, runtime authors and the like can use:
func bool2int(b bool) int {
var i int
if b {
i = 1
} else {
i = 0
}
return i
}
This compiles to:
"".bool2int t=1 size=16 args=0x10 locals=0x0
0x0000 00000 (x.go:25) TEXT "".bool2int(SB), $0-16
0x0000 00000 (x.go:25) FUNCDATA $0, gclocals·23e8278e2b69a3a75fa59b23c49ed6ad(SB)
0x0000 00000 (x.go:25) FUNCDATA $1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
0x0000 00000 (x.go:32) MOVBLZX "".b+8(FP), AX
0x0005 00005 (x.go:32) MOVBQZX AL, AX
0x0008 00008 (x.go:32) MOVQ AX, "".~r1+16(FP)
0x000d 00013 (x.go:32) RET
The extraneous MOVBQZX is #15300.
This optimization also helps range and slice.
The compiler must protect against pointers pointing
to the end of a slice/string. It does this by increasing
a pointer by either 0 or 1 * elemsize, based on a condition.
This CL optimizes away a jump in that code.
This CL triggers 382 times while compiling the standard library.
Updating code to utilize this optimization is left for future CLs.
Updates #6011
Change-Id: Ia7c1185f8aa223c543f91a3cd6d4a2a09c691c70
Reviewed-on: https://go-review.googlesource.com/22711
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
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|---|---|---|
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| doc | ||
| lib/time | ||
| misc | ||
| src | ||
| test | ||
| .gitattributes | ||
| .gitignore | ||
| AUTHORS | ||
| CONTRIBUTING.md | ||
| CONTRIBUTORS | ||
| favicon.ico | ||
| LICENSE | ||
| PATENTS | ||
| README.md | ||
| robots.txt | ||
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