cmd/compile: remove values from const cache upon free

When calling freeValue for possible const values, remove them from the
cache as well.

Change-Id: I087ed592243e33c58e5db41700ab266fc70196d9
Reviewed-on: https://go-review.googlesource.com/20481
Run-TryBot: Todd Neal <tolchz@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

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

@@ -116,6 +116,19 @@ func (f *Func) freeValue(v *Value) {
 	}
 	// Clear everything but ID (which we reuse).
 	id := v.ID
+
+	// Zero argument values might be cached, so remove them there.
+	nArgs := opcodeTable[v.Op].argLen
+	if nArgs == 0 {
+		vv := f.constants[v.AuxInt]
+		for i, cv := range vv {
+			if v == cv {
+				vv[i] = vv[len(vv)-1]
+				f.constants[v.AuxInt] = vv[0 : len(vv)-1]
+				break
+			}
+		}
+	}
 	*v = Value{}
 	v.ID = id
 	v.argstorage[0] = f.freeValues
@@ -280,6 +293,9 @@ func (f *Func) constVal(line int32, op Op, t Type, c int64, setAux bool) *Value
 	vv := f.constants[c]
 	for _, v := range vv {
 		if v.Op == op && v.Type.Equal(t) {
+			if setAux && v.AuxInt != c {
+				panic(fmt.Sprintf("cached const %s should have AuxInt of %d", v.LongString(), c))
+			}
 			return v
 		}
 	}

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

@@ -421,6 +421,28 @@ func TestEquiv(t *testing.T) {
 	}
 }
 
+// TestConstCache ensures that the cache will not return
+// reused free'd values with a non-matching AuxInt
+func TestConstCache(t *testing.T) {
+	f := Fun(testConfig(t), "entry",
+		Bloc("entry",
+			Valu("mem", OpInitMem, TypeMem, 0, nil),
+			Exit("mem")))
+	v1 := f.f.ConstBool(0, TypeBool, false)
+	v2 := f.f.ConstBool(0, TypeBool, true)
+	f.f.freeValue(v1)
+	f.f.freeValue(v2)
+	v3 := f.f.ConstBool(0, TypeBool, false)
+	v4 := f.f.ConstBool(0, TypeBool, true)
+	if v3.AuxInt != 0 {
+		t.Errorf("expected %s to have auxint of 0\n", v3.LongString())
+	}
+	if v4.AuxInt != 1 {
+		t.Errorf("expected %s to have auxint of 1\n", v4.LongString())
+	}
+
+}
+
 // opcodeMap returns a map from opcode to the number of times that opcode
 // appears in the function.
 func opcodeMap(f *Func) map[Op]int {