cmd/compile: zero all three argstorage slots

These changes were missed when going from 2 to 3 argstorage slots.
https://go-review.googlesource.com/20296/

Change-Id: I930a307bb0b695bf1ae088030c9bbb6d14ca31d2
Reviewed-on: https://go-review.googlesource.com/21841Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

src/cmd/compile/internal/ssa/func.go

@@ -284,7 +284,10 @@ func (b *Block) NewValue2I(line int32, op Op, t Type, auxint int64, arg0, arg1 *
 func (b *Block) NewValue3(line int32, op Op, t Type, arg0, arg1, arg2 *Value) *Value {
 	v := b.Func.newValue(op, t, b, line)
 	v.AuxInt = 0
-	v.Args = []*Value{arg0, arg1, arg2}
+	v.Args = v.argstorage[:3]
+	v.argstorage[0] = arg0
+	v.argstorage[1] = arg1
+	v.argstorage[2] = arg2
 	arg0.Uses++
 	arg1.Uses++
 	arg2.Uses++
@@ -295,7 +298,10 @@ func (b *Block) NewValue3(line int32, op Op, t Type, arg0, arg1, arg2 *Value) *V
 func (b *Block) NewValue3I(line int32, op Op, t Type, auxint int64, arg0, arg1, arg2 *Value) *Value {
 	v := b.Func.newValue(op, t, b, line)
 	v.AuxInt = auxint
-	v.Args = []*Value{arg0, arg1, arg2}
+	v.Args = v.argstorage[:3]
+	v.argstorage[0] = arg0
+	v.argstorage[1] = arg1
+	v.argstorage[2] = arg2
 	arg0.Uses++
 	arg1.Uses++
 	arg2.Uses++

src/cmd/compile/internal/ssa/value.go

@@ -185,6 +185,7 @@ func (v *Value) resetArgs() {
 	}
 	v.argstorage[0] = nil
 	v.argstorage[1] = nil
+	v.argstorage[2] = nil
 	v.Args = v.argstorage[:0]
 }