cmd/compile: remove check that Zero's arg has the correct base type
It doesn't have to. The type in the aux field is authoritative.
There are cases involving casting from interface{} where pointers
have a placeholder pointer type (because the type is not known when
the IData op is generated).
The check was introduced in CL 13447.
Fixes #39459
Change-Id: Id77a57577806a271aeebd20bea5d92d08ee7aa6b
Reviewed-on: https://go-review.googlesource.com/c/go/+/239817
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
diff --git a/src/cmd/compile/internal/ssa/deadstore.go b/src/cmd/compile/internal/ssa/deadstore.go
index 88af7a6..0664013 100644
--- a/src/cmd/compile/internal/ssa/deadstore.go
+++ b/src/cmd/compile/internal/ssa/deadstore.go
@@ -73,9 +73,11 @@
}
// Walk backwards looking for dead stores. Keep track of shadowed addresses.
- // An "address" is an SSA Value which encodes both the address and size of
- // the write. This code will not remove dead stores to the same address
- // of different types.
+ // A "shadowed address" is a pointer and a size describing a memory region that
+ // is known to be written. We keep track of shadowed addresses in the shadowed
+ // map, mapping the ID of the address to the size of the shadowed region.
+ // Since we're walking backwards, writes to a shadowed region are useless,
+ // as they will be immediately overwritten.
shadowed.clear()
v := last
@@ -93,17 +95,13 @@
sz = v.AuxInt
}
if shadowedSize := int64(shadowed.get(v.Args[0].ID)); shadowedSize != -1 && shadowedSize >= sz {
- // Modify store into a copy
+ // Modify the store/zero into a copy of the memory state,
+ // effectively eliding the store operation.
if v.Op == OpStore {
// store addr value mem
v.SetArgs1(v.Args[2])
} else {
// zero addr mem
- typesz := v.Args[0].Type.Elem().Size()
- if sz != typesz {
- f.Fatalf("mismatched zero/store sizes: %d and %d [%s]",
- sz, typesz, v.LongString())
- }
v.SetArgs1(v.Args[1])
}
v.Aux = nil
diff --git a/test/fixedbugs/issue39459.go b/test/fixedbugs/issue39459.go
new file mode 100644
index 0000000..de78a17
--- /dev/null
+++ b/test/fixedbugs/issue39459.go
@@ -0,0 +1,22 @@
+// compile
+
+// 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 p
+
+type T struct { // big enough to be an unSSAable type
+ a, b, c, d, e, f int
+}
+
+func f(x interface{}, p *int) {
+ _ = *p // trigger nil check here, removing it from below
+ switch x := x.(type) {
+ case *T:
+ // Zero twice, so one of them will be removed by the deadstore pass
+ *x = T{}
+ *p = 0 // store op to prevent Zero ops from being optimized by the earlier opt pass rewrite rules
+ *x = T{}
+ }
+}
