Tested x86_64-pc-linux-gnu, OK for trunk?
-- >8 --
In this testcase, we were optimizing away the temporary for f(), but
C++17 and above are clear that there is a temporary, and because its
destructor has visible side-effects we can't optimize it away under the
as-if rule. So disable this optimization for TREE_ADDRESSABLE type.
I moved the declaration of volatile_p after the call to
gimple_fold_indirect_ref_rhs to minimize indentation changes; I don't see
any way the value of that flag could be affected by the call.
gcc/ChangeLog:
* gimplify.cc (gimplify_modify_expr_rhs): Don't optimize
x = *(A*)&<expr> to x = <expr> for a TREE_ADDRESSABLE type.
gcc/testsuite/ChangeLog:
* g++.dg/init/elide9.C: New test.
---
gcc/gimplify.cc | 15 ++++++++-------
gcc/testsuite/g++.dg/init/elide9.C | 25 +++++++++++++++++++++++++
2 files changed, 33 insertions(+), 7 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/init/elide9.C
diff --git a/gcc/gimplify.cc b/gcc/gimplify.cc
index 9e0e3429958..07e63538e5b 100644
--- a/gcc/gimplify.cc
+++ b/gcc/gimplify.cc
@@ -5601,7 +5601,7 @@ gimplify_modify_expr_rhs (tree *expr_p, tree *from_p,
tree *to_p,
}
break;
case INDIRECT_REF:
- {
+ if (!TREE_ADDRESSABLE (TREE_TYPE (*from_p)))
/* If we have code like
*(const A*)(A*)&x
@@ -5610,11 +5610,13 @@ gimplify_modify_expr_rhs (tree *expr_p, tree *from_p,
tree *to_p,
of "A"), treat the entire expression as identical to "x".
This kind of code arises in C++ when an object is bound
to a const reference, and if "x" is a TARGET_EXPR we want
- to take advantage of the optimization below. */
- bool volatile_p = TREE_THIS_VOLATILE (*from_p);
- tree t = gimple_fold_indirect_ref_rhs (TREE_OPERAND (*from_p, 0));
- if (t)
+ to take advantage of the optimization below. But not if
+ the type is TREE_ADDRESSABLE; then C++17 says that the
+ TARGET_EXPR needs to be a temporary. */
+ if (tree t
+ = gimple_fold_indirect_ref_rhs (TREE_OPERAND (*from_p, 0)))
{
+ bool volatile_p = TREE_THIS_VOLATILE (*from_p);
if (TREE_THIS_VOLATILE (t) != volatile_p)
{
if (DECL_P (t))
@@ -5627,8 +5629,7 @@ gimplify_modify_expr_rhs (tree *expr_p, tree *from_p,
tree *to_p,
ret = GS_OK;
changed = true;
}
- break;
- }
+ break;
case TARGET_EXPR:
{
diff --git a/gcc/testsuite/g++.dg/init/elide9.C
b/gcc/testsuite/g++.dg/init/elide9.C
new file mode 100644
index 00000000000..810d60a94a4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/init/elide9.C
@@ -0,0 +1,25 @@
+// The static_cast should prevent temporary elision.
+// { dg-do run { target c++11 } }
+
+int d;
+struct A
+{
+ int i;
+ A() { }
+ ~A() { ++d; }
+};
+
+A f() { return A(); }
+
+struct B
+{
+ A a;
+ B(): a(static_cast<A&&>(f())) {}
+};
+
+int main()
+{
+ { B b; }
+ if (d != 2)
+ return -1;
+}
base-commit: 966010b2eb4a4c52f139b63548533e7bbd74ec9c
--
2.31.1
