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* [gcc r10-10614] c++: Avoid -Wunused-value false positives on nullptr passed to ellipsis [PR100666]
@ 2022-05-10 8:18 Jakub Jelinek
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From: Jakub Jelinek @ 2022-05-10 8:18 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:589a0f34b1d176b62b064c9815c341b6abf48a2b
commit r10-10614-g589a0f34b1d176b62b064c9815c341b6abf48a2b
Author: Jakub Jelinek <jakub@redhat.com>
Date: Tue May 25 17:24:38 2021 +0200
c++: Avoid -Wunused-value false positives on nullptr passed to ellipsis [PR100666]
When passing expressions with decltype(nullptr) type with side-effects to
ellipsis, we pass (void *)0 instead, but for the side-effects evaluate them
on the lhs of a COMPOUND_EXPR. Unfortunately that means we warn about it
if the expression is a call to nodiscard marked function, even when the
result is really used, just needs to be transformed.
Fixed by adding a warning_sentinel.
2021-05-25 Jakub Jelinek <jakub@redhat.com>
PR c++/100666
* call.c (convert_arg_to_ellipsis): For expressions with NULLPTR_TYPE
and side-effects, temporarily disable -Wunused-result warning when
building COMPOUND_EXPR.
* g++.dg/cpp1z/nodiscard8.C: New test.
* g++.dg/cpp1z/nodiscard9.C: New test.
(cherry picked from commit ad52d89808a947264397e920d7483090d4108f7b)
Diff:
---
gcc/cp/call.c | 5 ++++-
gcc/testsuite/g++.dg/cpp1z/nodiscard8.C | 15 +++++++++++++++
gcc/testsuite/g++.dg/cpp1z/nodiscard9.C | 22 ++++++++++++++++++++++
3 files changed, 41 insertions(+), 1 deletion(-)
diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index f636ef4cb03..29e4a52b6c4 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -7968,7 +7968,10 @@ convert_arg_to_ellipsis (tree arg, tsubst_flags_t complain)
{
arg = mark_rvalue_use (arg);
if (TREE_SIDE_EFFECTS (arg))
- arg = cp_build_compound_expr (arg, null_pointer_node, complain);
+ {
+ warning_sentinel w(warn_unused_result);
+ arg = cp_build_compound_expr (arg, null_pointer_node, complain);
+ }
else
arg = null_pointer_node;
}
diff --git a/gcc/testsuite/g++.dg/cpp1z/nodiscard8.C b/gcc/testsuite/g++.dg/cpp1z/nodiscard8.C
new file mode 100644
index 00000000000..b5096acbea1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/nodiscard8.C
@@ -0,0 +1,15 @@
+// PR c++/100666
+// { dg-do compile { target c++11 } }
+
+[[nodiscard]] decltype(nullptr) bar ();
+extern void foo (...);
+template <typename T> void qux (T);
+
+void
+baz ()
+{
+ foo (bar ()); // { dg-bogus "ignoring return value of '\[^\n\r]*', declared with attribute 'nodiscard'" }
+ bar (); // { dg-warning "ignoring return value of '\[^\n\r]*', declared with attribute 'nodiscard'" }
+ auto x = bar (); // { dg-bogus "ignoring return value of '\[^\n\r]*', declared with attribute 'nodiscard'" }
+ qux (bar ()); // { dg-bogus "ignoring return value of '\[^\n\r]*', declared with attribute 'nodiscard'" }
+}
diff --git a/gcc/testsuite/g++.dg/cpp1z/nodiscard9.C b/gcc/testsuite/g++.dg/cpp1z/nodiscard9.C
new file mode 100644
index 00000000000..1315ccdbf7c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/nodiscard9.C
@@ -0,0 +1,22 @@
+// PR c++/100666
+// { dg-do compile { target c++11 } }
+
+struct S {};
+[[nodiscard]] S bar ();
+struct U { S s; };
+[[nodiscard]] U corge ();
+extern void foo (...);
+template <typename T> void qux (T);
+
+void
+baz ()
+{
+ foo (bar ()); // { dg-bogus "ignoring return value of '\[^\n\r]*', declared with attribute 'nodiscard'" }
+ bar (); // { dg-warning "ignoring return value of '\[^\n\r]*', declared with attribute 'nodiscard'" }
+ auto x = bar (); // { dg-bogus "ignoring return value of '\[^\n\r]*', declared with attribute 'nodiscard'" }
+ qux (bar ()); // { dg-bogus "ignoring return value of '\[^\n\r]*', declared with attribute 'nodiscard'" }
+ foo (corge ()); // { dg-bogus "ignoring return value of '\[^\n\r]*', declared with attribute 'nodiscard'" }
+ corge (); // { dg-warning "ignoring return value of '\[^\n\r]*', declared with attribute 'nodiscard'" }
+ auto y = corge (); // { dg-bogus "ignoring return value of '\[^\n\r]*', declared with attribute 'nodiscard'" }
+ qux (corge ()); // { dg-bogus "ignoring return value of '\[^\n\r]*', declared with attribute 'nodiscard'" }
+}
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