cmd/compile: transform some Phis into Or8.

func f(a, b bool) bool {
          return a || b
}

is now a single instructions (excluding loading and unloading the arguments):
      v10 = ORB <bool> v11 v12 : AX

Change-Id: Iff63399410cb46909f4318ea1c3f45a029f4aa5e
Reviewed-on: https://go-review.googlesource.com/21872
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

1 files changed, 36 insertions, 4 deletions

diff --git a/test/phiopt.go b/test/phiopt.go
index 9b9b701124..37caab0b51 100644
--- a/test/phiopt.go
+++ b/test/phiopt.go
@@ -1,8 +1,13 @@
 // +build amd64
 // errorcheck -0 -d=ssa/phiopt/debug=3
 
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
 package main
 
+//go:noinline
 func f0(a bool) bool {
 	x := false
 	if a {
@@ -10,9 +15,10 @@ func f0(a bool) bool {
 	} else {
 		x = false
 	}
-	return x // ERROR "converted OpPhi to OpCopy$"
+	return x // ERROR "converted OpPhi to Copy$"
 }
 
+//go:noinline
 func f1(a bool) bool {
 	x := false
 	if a {
@@ -20,23 +26,49 @@ func f1(a bool) bool {
 	} else {
 		x = true
 	}
-	return x // ERROR "converted OpPhi to OpNot$"
+	return x // ERROR "converted OpPhi to Not$"
 }
 
+//go:noinline
 func f2(a, b int) bool {
 	x := true
 	if a == b {
 		x = false
 	}
-	return x // ERROR "converted OpPhi to OpNot$"
+	return x // ERROR "converted OpPhi to Not$"
 }
 
+//go:noinline
 func f3(a, b int) bool {
 	x := false
 	if a == b {
 		x = true
 	}
-	return x // ERROR "converted OpPhi to OpCopy$"
+	return x // ERROR "converted OpPhi to Copy$"
+}
+
+//go:noinline
+func f4(a, b bool) bool {
+	return a || b // ERROR "converted OpPhi to Or8$"
+}
+
+//go:noinline
+func f5(a int, b bool) bool {
+	x := b
+	if a == 0 {
+		x = true
+	}
+	return x // ERROR "converted OpPhi to Or8$"
+}
+
+//go:noinline
+func f6(a int, b bool) bool {
+	x := b
+	if a == 0 {
+		// f6 has side effects so the OpPhi should not be converted.
+		x = f6(a, b)
+	}
+	return x
 }
 
 func main() {