decl alignment not respected

This patch cures a problem with ICF of read-only variables at the
intersection of -fsection-anchors, -ftree-loop-vectorize, and targets
with alignment restrictions.

What happens with the testcase is:
- "c" is referenced in a constructor, thus make_decl_rtl for "c",
- make_decl_rtl puts "c" in an anchor block (-fsection-anchors),
- anchor block contents can't move, so "c" alignment can't change by
  ipa_increase_alignment (-ftree-loop-vectorize),
- however "a" alignment can be increased,
- ICF aliases "a" to "c".
So we have a decl for "a" saying it is aligned to 128 bits, using mem
for "c" which is only 16 bit aligned.

	PR ipa/69990
gcc/
	* ipa-icf.c (sem_variable::merge): Do not merge an alias with
	larger alignment.
gcc/testsuite/
	gcc.dg/pr69990.c: New.

From-SVN: r233906

1 files changed, 10 insertions, 0 deletions

diff --git a/gcc/ipa-icf.c b/gcc/ipa-icf.c
index ef04c559bf4..d82eb879d05 100644
--- a/gcc/ipa-icf.c
+++ b/gcc/ipa-icf.c
@@ -2209,6 +2209,16 @@ sem_variable::merge (sem_item *alias_item)
 		 "adress of original and alias may be compared.\n\n");
       return false;
     }
+
+  if (DECL_ALIGN (original->decl) < DECL_ALIGN (alias->decl))
+    {
+      if (dump_file)
+	fprintf (dump_file, "Not unifying; "
+		 "original and alias have incompatible alignments\n\n");
+
+      return false;
+    }
+
   if (DECL_COMDAT_GROUP (original->decl) != DECL_COMDAT_GROUP (alias->decl))
     {
       if (dump_file)