1 files changed, 29 insertions, 8 deletions

diff --git a/src/cmd/compile/internal/ssa/rewrite.go b/src/cmd/compile/internal/ssa/rewrite.go
index fb35691296..09f94ef53e 100644
--- a/src/cmd/compile/internal/ssa/rewrite.go
+++ b/src/cmd/compile/internal/ssa/rewrite.go
@@ -20,7 +20,15 @@ import (
 	"path/filepath"
 )
 
-func applyRewrite(f *Func, rb blockRewriter, rv valueRewriter) {
+type deadValueChoice bool
+
+const (
+	leaveDeadValues  deadValueChoice = false
+	removeDeadValues                 = true
+)
+
+// deadcode indicates that rewrite should try to remove any values that become dead.
+func applyRewrite(f *Func, rb blockRewriter, rv valueRewriter, deadcode deadValueChoice) {
 	// repeat rewrites until we find no more rewrites
 	pendingLines := f.cachedLineStarts // Holds statement boundaries that need to be moved to a new value/block
 	pendingLines.clear()
@@ -56,6 +64,18 @@ func applyRewrite(f *Func, rb blockRewriter, rv valueRewriter) {
 					*v0 = *v
 					v0.Args = append([]*Value{}, v.Args...) // make a new copy, not aliasing
 				}
+				if v.Uses == 0 && v.removeable() {
+					if v.Op != OpInvalid && deadcode == removeDeadValues {
+						// Reset any values that are now unused, so that we decrement
+						// the use count of all of its arguments.
+						// Not quite a deadcode pass, because it does not handle cycles.
+						// But it should help Uses==1 rules to fire.
+						v.reset(OpInvalid)
+						change = true
+					}
+					// No point rewriting values which aren't used.
+					continue
+				}
 
 				vchange := phielimValue(v)
 				if vchange && debug > 1 {
@@ -631,6 +651,10 @@ func auxIntToFlagConstant(x int64) flagConstant {
 	return flagConstant(x)
 }
 
+func auxIntToOp(cc int64) Op {
+	return Op(cc)
+}
+
 func boolToAuxInt(b bool) int64 {
 	if b {
 		return 1
@@ -674,6 +698,10 @@ func flagConstantToAuxInt(x flagConstant) int64 {
 	return int64(x)
 }
 
+func opToAuxInt(o Op) int64 {
+	return int64(o)
+}
+
 func auxToString(i interface{}) string {
 	return i.(string)
 }
@@ -707,13 +735,6 @@ func s390xCCMaskToAux(c s390x.CCMask) interface{} {
 func s390xRotateParamsToAux(r s390x.RotateParams) interface{} {
 	return r
 }
-func cCopToAux(o Op) interface{} {
-	return o
-}
-
-func auxToCCop(cc interface{}) Op {
-	return cc.(Op)
-}
 
 // uaddOvf reports whether unsigned a+b would overflow.
 func uaddOvf(a, b int64) bool {