cmd/compile: fix SSA type comparison

A typo in the conversion code caused comparisons of SSA types to
report CMPeq when they were not in fact equal.

Fixes #40837

Change-Id: I0627eee51d524a585908b34a4590bc533c8415fc
Reviewed-on: https://go-review.googlesource.com/c/go/+/248781
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

2 files changed, 30 insertions, 1 deletions

diff --git a/src/cmd/compile/internal/types/type.go b/src/cmd/compile/internal/types/type.go
index 3b7b31c5d6..91b54b43d4 100644
--- a/src/cmd/compile/internal/types/type.go
+++ b/src/cmd/compile/internal/types/type.go
@@ -131,6 +131,7 @@ type Type struct {
 	// TPTR: Ptr
 	// TARRAY: *Array
 	// TSLICE: Slice
+	// TSSA: string
 	Extra interface{}
 
 	// Width is the width of this Type in bytes.
@@ -1026,7 +1027,7 @@ func (t *Type) cmp(x *Type) Cmp {
 
 	case TSSA:
 		tname := t.Extra.(string)
-		xname := t.Extra.(string)
+		xname := x.Extra.(string)
 		// desire fast sorting, not pretty sorting.
 		if len(tname) == len(xname) {
 			if tname == xname {
diff --git a/src/cmd/compile/internal/types/type_test.go b/src/cmd/compile/internal/types/type_test.go
new file mode 100644
index 0000000000..fe3f380b21
--- /dev/null
+++ b/src/cmd/compile/internal/types/type_test.go
@@ -0,0 +1,28 @@
+// Copyright 2020 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 types_test
+
+import (
+	"cmd/compile/internal/types"
+	"testing"
+)
+
+func TestSSACompare(t *testing.T) {
+	a := []*types.Type{
+		types.TypeInvalid,
+		types.TypeMem,
+		types.TypeFlags,
+		types.TypeVoid,
+		types.TypeInt128,
+	}
+	for _, x := range a {
+		for _, y := range a {
+			c := x.Compare(y)
+			if x == y && c != types.CMPeq || x != y && c == types.CMPeq {
+				t.Errorf("%s compare %s == %d\n", x.Extra, y.Extra, c)
+			}
+		}
+	}
+}