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author | Jason Merrill <jason@redhat.com> | 2022-10-05 11:50:59 -0400 |
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committer | Jason Merrill <jason@redhat.com> | 2022-10-07 09:22:32 -0400 |
commit | d3e5465757c599ea64f611290b7793d3141a6b7c (patch) | |
tree | 42223c603e13701c6d5569b2960677af795ca609 /gcc | |
parent | 89228e3985c5cdf6be58a3b5b1afcad91e9e3422 (diff) | |
download | gcc-d3e5465757c599ea64f611290b7793d3141a6b7c.zip gcc-d3e5465757c599ea64f611290b7793d3141a6b7c.tar.gz gcc-d3e5465757c599ea64f611290b7793d3141a6b7c.tar.bz2 |
gimplify: prevent some C++ temporary elision
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.
Diffstat (limited to 'gcc')
-rw-r--r-- | gcc/gimplify.cc | 15 | ||||
-rw-r--r-- | gcc/testsuite/g++.dg/init/elide9.C | 25 |
2 files changed, 33 insertions, 7 deletions
diff --git a/gcc/gimplify.cc b/gcc/gimplify.cc index 95e16f6..d4209ea 100644 --- a/gcc/gimplify.cc +++ b/gcc/gimplify.cc @@ -5620,7 +5620,7 @@ 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 @@ -5629,11 +5629,13 @@ 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)) @@ -5646,8 +5648,7 @@ 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 0000000..810d60a --- /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; +} |