[gcc(refs/vendors/redhat/heads/gcc-8-branch)] c++: Bogus error with alignof [PR90736]

[Jakub Jelinek <jakub@gcc.gnu.org>]

https://gcc.gnu.org/g:4dc2d0cabe9b3986078cb62bd1d2f71707f4156a

commit 4dc2d0cabe9b3986078cb62bd1d2f71707f4156a
Author: Marek Polacek <polacek@redhat.com>
Date:   Mon May 4 13:25:42 2020 -0400

    c++: Bogus error with alignof [PR90736]
    
            PR c++/90736 - bogus error with alignof.
            * constexpr.c (adjust_temp_type): Use cv_unqualified type.

Diff:
---
 gcc/cp/ChangeLog                      | 8 ++++++++
 gcc/cp/constexpr.c                    | 4 +++-
 gcc/testsuite/g++.dg/cpp0x/alignof5.C | 6 ++++++
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index d1d829a8bca..ebebbe29e38 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,11 @@
+2020-05-04  Marek Polacek  <polacek@redhat.com>
+
+	Backported from mainline
+	2019-06-12  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/90736 - bogus error with alignof.
+	* constexpr.c (adjust_temp_type): Use cv_unqualified type.
+
 2020-04-04  Jason Merrill  <jason@redhat.com>
 
 	PR c++/91377
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index bebe72e4db9..f68ad758a14 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -1255,7 +1255,9 @@ adjust_temp_type (tree type, tree temp)
   if (TREE_CODE (temp) == EMPTY_CLASS_EXPR)
     return build0 (EMPTY_CLASS_EXPR, type);
   gcc_assert (scalarish_type_p (type));
-  return cp_fold_convert (type, temp);
+  /* Now we know we're dealing with a scalar, and a prvalue of non-class
+     type is cv-unqualified.  */
+  return cp_fold_convert (cv_unqualified (type), temp);
 }
 
 /* Callback for walk_tree used by unshare_constructor.  */
diff --git a/gcc/testsuite/g++.dg/cpp0x/alignof5.C b/gcc/testsuite/g++.dg/cpp0x/alignof5.C
new file mode 100644
index 00000000000..09354d3e1d0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/alignof5.C
@@ -0,0 +1,6 @@
+// PR c++/90736 - bogus error with alignof.
+// { dg-do compile { target c++11 } }
+
+constexpr int fn(const int b) { return b; }
+constexpr int c = fn(alignof(int));
+alignas(c) char d;