Re: [PATCH RFA] c-family: attribute ((aligned, mode)) [PR100545]

[Jason Merrill <jason@redhat.com>]

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On 4/27/22 13:02, Joseph Myers wrote:
> On Wed, 27 Apr 2022, Jason Merrill via Gcc-patches wrote:
> 
>> +      if (typedef_variant_p (type))
>> +	{
>> +	  /* Set up the typedef all over again.  */
> 
> This seems wrong when the typedef is just being used in another
> declaration with the mode attribute, as opposed to being defined using the
> mode attribute.  E.g. the following test is valid and accepted before the
> patch, but wrongly rejected after the patch because the typedef has had
> its type changed.
> 
> typedef int I;
> int x;
> I y __attribute__ ((mode(QI)));
> extern I x;

Ah, good point.  Fixed thus:

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From 35210478aa12623dcf027b7a14ea5216d93a46e4 Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Fri, 15 Apr 2022 16:27:05 -0400
Subject: [PATCH] c-family: attribute ((aligned, mode)) [PR100545]
To: gcc-patches@gcc.gnu.org

The problem here was that handle_mode_attribute clobbered the changes of any
previous attribute, only copying type qualifiers to the new type.  And
common_handle_aligned_attribute had previously set up the typedef, so when
we later called set_underlying_type it saw DECL_ORIGINAL_TYPE set and just
returned, even though handle_mode_attribute had messed up the TREE_TYPE.
So, let's fix handle_mode_attribute to copy attributes, alignment, and
typedefness to the new type.

	PR c/100545

gcc/c-family/ChangeLog:

	* c-attribs.cc (handle_mode_attribute): Copy attributes, aligned,
	and typedef.
	* c-common.cc (set_underlying_type): Add assert.

gcc/testsuite/ChangeLog:

	* c-c++-common/attr-mode-1.c: New test.
	* c-c++-common/attr-mode-2.c: New test.
---
 gcc/c-family/c-attribs.cc                | 16 +++++++++++++++-
 gcc/c-family/c-common.cc                 |  7 ++++---
 gcc/testsuite/c-c++-common/attr-mode-1.c |  3 +++
 gcc/testsuite/c-c++-common/attr-mode-2.c |  4 ++++
 4 files changed, 26 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/c-c++-common/attr-mode-1.c
 create mode 100644 gcc/testsuite/c-c++-common/attr-mode-2.c

diff --git a/gcc/c-family/c-attribs.cc b/gcc/c-family/c-attribs.cc
index 111a33f405a..b1953a45f9b 100644
--- a/gcc/c-family/c-attribs.cc
+++ b/gcc/c-family/c-attribs.cc
@@ -2199,7 +2199,21 @@ handle_mode_attribute (tree *node, tree name, tree args,
 	  return NULL_TREE;
 	}
 
-      *node = build_qualified_type (typefm, TYPE_QUALS (type));
+      /* Copy any quals and attributes to the new type.  */
+      *node = build_type_attribute_qual_variant (typefm, TYPE_ATTRIBUTES (type),
+						 TYPE_QUALS (type));
+      if (TYPE_USER_ALIGN (type))
+	*node = build_aligned_type (*node, TYPE_ALIGN (type));
+
+      tree decl = node[2];
+      if (decl && TYPE_NAME (type) == decl)
+	{
+	  /* Set up the typedef all over again.  */
+	  DECL_ORIGINAL_TYPE (decl) = NULL_TREE;
+	  TREE_TYPE (decl) = *node;
+	  set_underlying_type (decl);
+	  *node = TREE_TYPE (decl);
+	}
     }
 
   return NULL_TREE;
diff --git a/gcc/c-family/c-common.cc b/gcc/c-family/c-common.cc
index bb0544eeaea..730faa9e87f 100644
--- a/gcc/c-family/c-common.cc
+++ b/gcc/c-family/c-common.cc
@@ -8153,15 +8153,16 @@ check_missing_format_attribute (tree ltype, tree rtype)
 void
 set_underlying_type (tree x)
 {
-  if (x == error_mark_node)
+  if (x == error_mark_node || TREE_TYPE (x) == error_mark_node)
     return;
   if (DECL_IS_UNDECLARED_BUILTIN (x) && TREE_CODE (TREE_TYPE (x)) != ARRAY_TYPE)
     {
       if (TYPE_NAME (TREE_TYPE (x)) == 0)
 	TYPE_NAME (TREE_TYPE (x)) = x;
     }
-  else if (TREE_TYPE (x) != error_mark_node
-	   && DECL_ORIGINAL_TYPE (x) == NULL_TREE)
+  else if (DECL_ORIGINAL_TYPE (x))
+    gcc_checking_assert (TYPE_NAME (TREE_TYPE (x)) == x);
+  else
     {
       tree tt = TREE_TYPE (x);
       DECL_ORIGINAL_TYPE (x) = tt;
diff --git a/gcc/testsuite/c-c++-common/attr-mode-1.c b/gcc/testsuite/c-c++-common/attr-mode-1.c
new file mode 100644
index 00000000000..59b20cd99e8
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attr-mode-1.c
@@ -0,0 +1,3 @@
+// PR c/100545
+
+typedef int fatp_t __attribute__((aligned, mode(SI)));
diff --git a/gcc/testsuite/c-c++-common/attr-mode-2.c b/gcc/testsuite/c-c++-common/attr-mode-2.c
new file mode 100644
index 00000000000..de65f49c6b6
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attr-mode-2.c
@@ -0,0 +1,4 @@
+typedef int I;
+int x;
+I y __attribute__ ((mode(QI)));
+extern I x;
-- 
2.27.0