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

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.

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 46208b2d7561b374653681067de1b9343b665d7b..5b8c5e329db41441a56dd4b9929d38a52bafe07d 100644 (file)
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -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.

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index bae4b2c0f5214a30e31fac9abbc38e26ad03ec0f..02220ffb3a15a04cdb07164357049a5dcaae97b7 100644 (file)
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -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;
 }

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index f0b1b5f006b41aa48de097c224188ad399e8155c..5f9b164d4863caa85375caa0e2be66fd92c5ab0d 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -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.

diff --git a/gcc/testsuite/g++.dg/other/pr94326.C b/gcc/testsuite/g++.dg/other/pr94326.C
new file mode 100644 (file)
index 0000000..4069c03
--- /dev/null
+++ b/gcc/testsuite/g++.dg/other/pr94326.C
@@ -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{});
+}