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c++: Avoid calls in non-evaluated contexts affect whether function can or can't throw [PR94326]

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The following testcase FAILs -fcompare-debug, because if we emit a
-Wreturn-local-addr warning, we tsubst decltype in order to print the
warning and as that function could throw, set_flags_from_callee during that
sets cp_function_chain->can_throw and later on we don't set TREE_NOTHROW
on foo.  While with -w or -Wno-return-local-addr, tsubst isn't called during
the warning_at, cp_function_chain->can_throw is kept clear and TREE_NOTHROW
is set on foo.
It isn't just a matter of the warning though, in
int foo ();
int bar () { return sizeof (foo ()); }
int baz () { return sizeof (int); }
I don't really see why we should mark only baz as TREE_NOTHROW and not bar
too, when neither can really throw.

2020-03-27  Jakub Jelinek  <jakub@redhat.com>

	PR c++/94326
	* call.c (set_flags_from_callee): Don't update
	cp_function_chain->can_throw or current_function_returns_abnormally
	if cp_unevaluated_operand.

	* g++.dg/other/pr94326.C: New test.
This commit is contained in:
Jakub Jelinek 2020-03-27 10:04:31 +01:00
parent 72809d6fe8
commit 2eea00c518
4 changed files with 34 additions and 4 deletions
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5
gcc/cp/ChangeLog
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@ -1,5 +1,10 @@
2020-03-27 Jakub Jelinek <jakub@redhat.com>
PR c++/94326
* call.c (set_flags_from_callee): Don't update
cp_function_chain->can_throw or current_function_returns_abnormally
if cp_unevaluated_operand.
PR c++/94339
* cvt.c (ocp_convert): Handle COMPOUND_EXPR by recursion on the second
operand and creating a new COMPOUND_EXPR if anything changed.

11
gcc/cp/call.c
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@ -333,11 +333,14 @@ set_flags_from_callee (tree call)
&& internal_fn_flags (CALL_EXPR_IFN (call)) & ECF_NOTHROW)
nothrow = true;
if (!nothrow && at_function_scope_p () && cfun && cp_function_chain)
cp_function_chain->can_throw = 1;
if (cfun && cp_function_chain && !cp_unevaluated_operand)
{
if (!nothrow && at_function_scope_p ())
cp_function_chain->can_throw = 1;
if (decl && TREE_THIS_VOLATILE (decl) && cfun && cp_function_chain)
current_function_returns_abnormally = 1;
if (decl && TREE_THIS_VOLATILE (decl))
current_function_returns_abnormally = 1;
}
TREE_NOTHROW (call) = nothrow;
}

3
gcc/testsuite/ChangeLog
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@ -1,5 +1,8 @@
2020-03-27 Jakub Jelinek <jakub@redhat.com>
PR c++/94326
* g++.dg/other/pr94326.C: New test.
PR c++/94339
* g++.dg/other/pr94339.C: New test.
* g++.dg/ext/attr-copy-2.C: Comment out failing tests due to PR94346.

19
gcc/testsuite/g++.dg/other/pr94326.C Normal file
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@ -0,0 +1,19 @@
// PR c++/94326
// { dg-do compile { target c++11 } }
// { dg-options "-fcompare-debug" }
template <typename = int> struct A {
const int &foo() { return 0; } // { dg-warning "returning reference to temporary" }
template <typename _Kt> void bar(_Kt) { foo(); }
};
struct B {
A<> b;
template <typename _Kt> auto baz(_Kt p1) -> decltype(b.bar(p1)) {
b.bar(p1);
}
};
struct C {};
void operator<(C, int) {
B a;
a.baz(C{});
}