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author | Josh Bleecher Snyder <josharian@gmail.com> | 2016-05-02 16:16:46 -0700 |
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committer | Josh Bleecher Snyder <josharian@gmail.com> | 2016-08-16 17:14:52 +0000 |
commit | e85265e8c2a41e4a0e703e5fb6fe762cc382d0af (patch) | |
tree | 884f6417ded5d3786b1f890e6ce0134f156c4209 | |
parent | c7b9bd745642677c8d4b3b76803a39b4e50b4d81 (diff) | |
download | go-e85265e8c2a41e4a0e703e5fb6fe762cc382d0af.tar.gz go-e85265e8c2a41e4a0e703e5fb6fe762cc382d0af.zip |
cmd/compile: optimize bool to int conversion
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>
-rw-r--r-- | src/cmd/compile/internal/ssa/phiopt.go | 61 |
1 files changed, 60 insertions, 1 deletions
diff --git a/src/cmd/compile/internal/ssa/phiopt.go b/src/cmd/compile/internal/ssa/phiopt.go index d6272b4cfc..fd40eb593e 100644 --- a/src/cmd/compile/internal/ssa/phiopt.go +++ b/src/cmd/compile/internal/ssa/phiopt.go @@ -57,7 +57,16 @@ func phiopt(f *Func) { } for _, v := range b.Values { - if v.Op != OpPhi || !v.Type.IsBoolean() { + if v.Op != OpPhi { + continue + } + + // Look for conversions from bool to 0/1. + if v.Type.IsInteger() { + phioptint(v, b0, reverse) + } + + if !v.Type.IsBoolean() { continue } @@ -110,5 +119,55 @@ func phiopt(f *Func) { } } } +} + +func phioptint(v *Value, b0 *Block, reverse int) { + a0 := v.Args[0] + a1 := v.Args[1] + if a0.Op != a1.Op { + return + } + + switch a0.Op { + case OpConst8, OpConst16, OpConst32, OpConst64: + default: + return + } + negate := false + switch { + case a0.AuxInt == 0 && a1.AuxInt == 1: + negate = true + case a0.AuxInt == 1 && a1.AuxInt == 0: + default: + return + } + + if reverse == 1 { + negate = !negate + } + + switch v.Type.Size() { + case 1: + v.reset(OpCopy) + case 2: + v.reset(OpZeroExt8to16) + case 4: + v.reset(OpZeroExt8to32) + case 8: + v.reset(OpZeroExt8to64) + default: + v.Fatalf("bad int size %d", v.Type.Size()) + } + + a := b0.Control + if negate { + a = v.Block.NewValue1(v.Line, OpNot, a.Type, a) + } + v.AddArg(a) + + f := b0.Func + if f.pass.debug > 0 { + f.Config.Warnl(v.Block.Line, "converted OpPhi bool -> int%d", v.Type.Size()*8) + } } |