Re: [PATCH] c++: -Wdangling-reference not suppressed in template [PR109774]

[Jason Merrill via Gcc-patches]

On 5/16/23 15:13, Marek Polacek wrote:

In check_return_expr, we suppress the -Wdangling-reference warning when
we're sure it would be a false positive.  It wasn't working in a
template, though, because the suppress_warning call was never reached.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk and 13.2?


OK.


PR c++/109774

gcc/cp/ChangeLog:

* typeck.cc (check_return_expr): In a template, return only after
suppressing -Wdangling-reference.

gcc/testsuite/ChangeLog:

* g++.dg/warn/Wdangling-reference13.C: New test.
---
  gcc/cp/typeck.cc  |  6 ++---
  .../g++.dg/warn/Wdangling-reference13.C   | 23 +++
  2 files changed, 26 insertions(+), 3 deletions(-)
  create mode 100644 gcc/testsuite/g++.dg/warn/Wdangling-reference13.C

diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index 53ac925a092..c225c4e2423 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -11236,9 +11236,6 @@ check_return_expr (tree retval, bool *no_warning)
 build_zero_cst (TREE_TYPE (retval)));
  }
  
-  if (processing_template_decl)

-return saved_retval;
-
/* A naive attempt to reduce the number of -Wdangling-reference false
   positives: if we know that this function can return a variable with
   static storage duration rather than one of its parameters, suppress
@@ -11250,6 +11247,9 @@ check_return_expr (tree retval, bool *no_warning)
&& TREE_STATIC (bare_retval))
  suppress_warning (current_function_decl, OPT_Wdangling_reference);
  
+  if (processing_template_decl)

+return saved_retval;
+
/* Actually copy the value returned into the appropriate location.  */
if (retval && retval != result)
  {
diff --git a/gcc/testsuite/g++.dg/warn/Wdangling-reference13.C 
b/gcc/testsuite/g++.dg/warn/Wdangling-reference13.C
new file mode 100644
index 000..bc09fbae22b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wdangling-reference13.C
@@ -0,0 +1,23 @@
+// PR c++/109774
+// { dg-do compile }
+// { dg-options "-Wdangling-reference" }
+
+int y;
+
+template
+int& get(const char& )
+{
+return y;
+}
+
+int& get2(const char&)
+{
+return y;
+}
+
+int stuff(void)
+{
+const int  = get(0); // { dg-bogus "dangling reference" }
+const int  = get2(0); // { dg-bogus "dangling reference" }
+return h+k;
+}

base-commit: 94a311abf783de754f0f1b2d4c1f00a9788e795b

[PATCH] c++: -Wdangling-reference not suppressed in template [PR109774]

[Marek Polacek via Gcc-patches]

In check_return_expr, we suppress the -Wdangling-reference warning when
we're sure it would be a false positive.  It wasn't working in a
template, though, because the suppress_warning call was never reached.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk and 13.2?

PR c++/109774

gcc/cp/ChangeLog:

* typeck.cc (check_return_expr): In a template, return only after
suppressing -Wdangling-reference.

gcc/testsuite/ChangeLog:

* g++.dg/warn/Wdangling-reference13.C: New test.
---
 gcc/cp/typeck.cc  |  6 ++---
 .../g++.dg/warn/Wdangling-reference13.C   | 23 +++
 2 files changed, 26 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/warn/Wdangling-reference13.C

diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index 53ac925a092..c225c4e2423 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -11236,9 +11236,6 @@ check_return_expr (tree retval, bool *no_warning)
 build_zero_cst (TREE_TYPE (retval)));
 }
 
-  if (processing_template_decl)
-return saved_retval;
-
   /* A naive attempt to reduce the number of -Wdangling-reference false
  positives: if we know that this function can return a variable with
  static storage duration rather than one of its parameters, suppress
@@ -11250,6 +11247,9 @@ check_return_expr (tree retval, bool *no_warning)
   && TREE_STATIC (bare_retval))
 suppress_warning (current_function_decl, OPT_Wdangling_reference);
 
+  if (processing_template_decl)
+return saved_retval;
+
   /* Actually copy the value returned into the appropriate location.  */
   if (retval && retval != result)
 {
diff --git a/gcc/testsuite/g++.dg/warn/Wdangling-reference13.C 
b/gcc/testsuite/g++.dg/warn/Wdangling-reference13.C
new file mode 100644
index 000..bc09fbae22b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wdangling-reference13.C
@@ -0,0 +1,23 @@
+// PR c++/109774
+// { dg-do compile }
+// { dg-options "-Wdangling-reference" }
+
+int y;
+
+template
+int& get(const char& )
+{
+return y;
+}
+
+int& get2(const char&)
+{
+return y;
+}
+
+int stuff(void)
+{
+const int  = get(0); // { dg-bogus "dangling reference" }
+const int  = get2(0); // { dg-bogus "dangling reference" }
+return h+k;
+}

base-commit: 94a311abf783de754f0f1b2d4c1f00a9788e795b
-- 
2.40.1