cmd/compile: do not reuse dead value in expand_calls pass

We reuse a value for the same selector on the same arg. But if the
value is already marked dead, don't reuse it. A use of an
OpInvalid will confuse the compiler.

Fixes #48916.

Change-Id: I15b9e15b49f6e1991fe91df246cd12a193385e85
Reviewed-on: https://go-review.googlesource.com/c/go/+/355409
Trust: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

diff --git a/src/cmd/compile/internal/ssa/expand_calls.go b/src/cmd/compile/internal/ssa/expand_calls.go
index a0f0e653aa41041dda93ecc88ac43a9e26b91fe5..18c9ab696d5d0e011210d669f6c1b30f9fcbf3cc 100644 (file)
--- a/src/cmd/compile/internal/ssa/expand_calls.go
+++ b/src/cmd/compile/internal/ssa/expand_calls.go
@@ -1678,7 +1678,7 @@ func (x *expandState) rewriteArgToMemOrRegs(v *Value) *Value {
                t := v.Type
                key := selKey{v, 0, t.Size(), t}
                w := x.commonArgs[key]
-               if w != nil {
+               if w != nil && w.Uses != 0 { // do not reuse dead value
                        v.copyOf(w)
                        break
                }
@@ -1709,9 +1709,15 @@ func (x *expandState) newArgToMemOrRegs(baseArg, toReplace *Value, offset int64,
        }
        key := selKey{baseArg, offset, t.Size(), t}
        w := x.commonArgs[key]
-       if w != nil {
+       if w != nil && w.Uses != 0 { // do not reuse dead value
                if toReplace != nil {
                        toReplace.copyOf(w)
+                       if x.debug > 1 {
+                               x.Printf("...replace %s\n", toReplace.LongString())
+                       }
+               }
+               if x.debug > 1 {
+                       x.Printf("-->%s\n", w.LongString())
                }
                return w
        }

diff --git a/test/fixedbugs/issue48916.go b/test/fixedbugs/issue48916.go
new file mode 100644 (file)
index 0000000..cbe97b5
--- /dev/null
+++ b/test/fixedbugs/issue48916.go
@@ -0,0 +1,37 @@
+// compile
+
+// Copyright 2021 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.
+
+// Issue 48916: expand_calls pass crashes due to a (dead)
+// use of an OpInvalid value.
+
+package p
+
+type T struct {
+       num int64
+}
+
+func foo(vs map[T]struct{}, d T) error {
+       _, ok := vs[d]
+       if !ok {
+               return nil
+       }
+
+       switch d.num {
+       case 0:
+       case 1:
+       case 2:
+       case 3:
+       case 4:
+       case 5:
+       case 6:
+               var num float64
+               if num != 0 {
+                       return nil
+               }
+       }
+
+       return nil
+}