[gcc(refs/vendors/ARM/heads/arm-perf-staging)] c++: Fix bogus -Wparentheses warning with fold-expression [PR94505]

[Tamar Christina]

https://gcc.gnu.org/g:5bdd4c5d3fc9c143e8edea3b10828e4b75d7a385

commit 5bdd4c5d3fc9c143e8edea3b10828e4b75d7a385
Author: Marek Polacek <polacek@redhat.com>
Date:   Sun Apr 19 12:12:01 2020 -0400

    c++: Fix bogus -Wparentheses warning with fold-expression [PR94505]
    
    We issue bogus -Wparentheses warnings (3 of them!) for this fold expression:
    
      ((B && true) || ...)
    
    Firstly, issuing a warning for a compiler-generated expression is wrong
    and secondly, B && true must be wrapped in ( ) otherwise you'll get
    error: binary expression in operand of fold-expression.
    
            PR c++/94505 - bogus -Wparentheses warning with fold-expression.
            * pt.c (fold_expression): Add warning_sentinel for -Wparentheses
            before calling build_x_binary_op.
    
            * g++.dg/cpp1z/fold11.C: New test.

Diff:
---
 gcc/cp/ChangeLog                    |  6 ++++++
 gcc/cp/pt.c                         |  1 +
 gcc/testsuite/ChangeLog             |  5 +++++
 gcc/testsuite/g++.dg/cpp1z/fold11.C | 12 ++++++++++++
 4 files changed, 24 insertions(+)

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 891ec79fcfd..52f199d90bf 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2020-04-20  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/94505 - bogus -Wparentheses warning with fold-expression.
+	* pt.c (fold_expression): Add warning_sentinel for -Wparentheses
+	before calling build_x_binary_op.
+
 2020-04-20  Marek Polacek  <polacek@redhat.com>
 
 	* coroutines.cc (captures_temporary): Don't assign the result of
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 4f4c04e7df8..899df9a330c 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -12379,6 +12379,7 @@ fold_expression (tree t, tree left, tree right, tsubst_flags_t complain)
   if (FOLD_EXPR_MODIFY_P (t))
     return build_x_modify_expr (input_location, left, code, right, complain);
 
+  warning_sentinel s(warn_parentheses);
   switch (code)
     {
     case COMPOUND_EXPR:
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index ce31ed0cd44..33f008b9af4 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-04-20  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/94505 - bogus -Wparentheses warning with fold-expression.
+	* g++.dg/cpp1z/fold11.C: New test.
+
 2020-04-20  Andreas Krebbel  <krebbel@linux.ibm.com>
 
 	* g++.dg/pr94666.C: New test.
diff --git a/gcc/testsuite/g++.dg/cpp1z/fold11.C b/gcc/testsuite/g++.dg/cpp1z/fold11.C
new file mode 100644
index 00000000000..09a30555eee
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/fold11.C
@@ -0,0 +1,12 @@
+// PR c++/94505 - bogus -Wparentheses warning with fold-expression.
+// { dg-do compile { target c++17 } }
+// { dg-options "-Wparentheses" }
+
+template <bool... B>
+bool foo () {
+    return ((B && true) || ...); // { dg-bogus "suggest parentheses" }
+}
+
+int main () {
+    foo<true, false, false, true> ();
+}