[dev.ssa] cmd/compile/internal/ssa/gen: move variable reset code into a function

Shaves about 3 lines per generated rule.

Change-Id: I94adc94ab79f90ac5fd033f896ece3b1eddf0f3d
Reviewed-on: https://go-review.googlesource.com/19197
Reviewed-by: Keith Randall <khr@golang.org>
diff --git a/src/cmd/compile/internal/ssa/value.go b/src/cmd/compile/internal/ssa/value.go
index af6bb3b..d71fd8f 100644
--- a/src/cmd/compile/internal/ssa/value.go
+++ b/src/cmd/compile/internal/ssa/value.go
@@ -170,6 +170,13 @@
 	v.Args = v.argstorage[:0]
 }
 
+func (v *Value) reset(op Op) {
+	v.Op = op
+	v.resetArgs()
+	v.AuxInt = 0
+	v.Aux = nil
+}
+
 // copyInto makes a new value identical to v and adds it to the end of b.
 func (v *Value) copyInto(b *Block) *Value {
 	c := b.NewValue0(v.Line, v.Op, v.Type)