forwprop: Fix copy prop for alignment after the final folding [PR122086]

After r16-4081-g966cdec2b2 which added folding of __builtin_assume_aligned,
forwprop would propagate pointers that lower alignment replacing ones with
greater alignment. This causes us to lose alignment information that
__builtin_assume_aligned provided to expand.  Normally this just loses some
optimizations except in the s390 case where the alignment is specifically
checked and was for inlining of the atomics; without this patch an infininite
loop would happen.

Note this was previously broken for -Og before r16-4081-g966cdec2b2. This
fixes -Og case as forwprop is used instead of copyprop.

This moves the testcase for pr107389.c to torture to get a generic testcase.
pr107389.c was originally for -O0 case but we should test for other
optimization levels so this is not lost again.

align-5.c is xfailed because __builtin_assume_aligned is not instrumented for ubsan
alignment and ubsan check to see pointer is aligned before emitting a check for the
load (based on the known alignment in compiling). See PR 122038 too. I had mentioned
this issue previously in r16-4081-g966cdec2b2 too.

	PR middle-end/107389
	PR tree-optimization/122086
gcc/ChangeLog:

	* tree-ssa-forwprop.cc (forwprop_may_propagate_copy): New function.
	(pass_forwprop::execute):  Use forwprop_may_propagate_copy
	instead of may_propagate_copy.

gcc/testsuite/ChangeLog:

	* gcc.dg/pr107389.c: Move to...
	* gcc.dg/torture/pr107389.c: ...here. Skip for lto.
	Use dg-additional-options rather than dg-options.
	* c-c++-common/ubsan/align-5.c: xfail.

Signed-off-by: Andrew Pinski <andrew.pinski@oss.qualcomm.com>

diff --git a/gcc/testsuite/c-c++-common/ubsan/align-5.c b/gcc/testsuite/c-c++-common/ubsan/align-5.c
index 484790134a66076203d4a380e94a73c6b03f275d..6d2ac26612bb89516eb8b1aa7e301ff234aa48a6 100644 (file)
--- a/gcc/testsuite/c-c++-common/ubsan/align-5.c
+++ b/gcc/testsuite/c-c++-common/ubsan/align-5.c
@@ -11,4 +11,6 @@ foo (char *p)
   return *q;
 }
 
-/* { dg-final { scan-assembler "__ubsan_handle" } } */
+/* xfail, see PR 122038 as __builtin_assume_aligned should be instrumented instead
+   of only the load. */
+/* { dg-final { scan-assembler "__ubsan_handle" { xfail *-*-* } } } */

diff --git a/gcc/testsuite/gcc.dg/pr107389.c b/gcc/testsuite/gcc.dg/torture/pr107389.c
similarity index 73%
rename from gcc/testsuite/gcc.dg/pr107389.c
rename to gcc/testsuite/gcc.dg/torture/pr107389.c
index deb633807044828ff31710dfead76709c84b8b80..23c2776ab736a1ffb724a0f693bffd21da0752f9 100644 (file)
--- a/gcc/testsuite/gcc.dg/pr107389.c
+++ b/gcc/testsuite/gcc.dg/torture/pr107389.c
@@ -1,5 +1,6 @@
 /* { dg-do compile } */
-/* { dg-options "-fdump-tree-optimized-alias" } */
+/* { dg-skip-if "" { *-*-* } { "-flto" } { "" } } */
+/* { dg-additional-options "-fdump-tree-optimized-alias" } */
 
 unsigned foo (void *p)
 {

diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
index 68e80baa46c0e580527e2f6710abcfb0ee4807a3..79ac25f7ed5752a13084e789939682f4e8fb5ee0 100644 (file)
--- a/gcc/tree-ssa-forwprop.cc
+++ b/gcc/tree-ssa-forwprop.cc
@@ -216,6 +216,31 @@ static bitmap to_purge;
 /* Const-and-copy lattice.  */
 static vec<tree> lattice;
 
+/* forwprop_may_propagate_copy is like may_propagate_copy except
+   after the final folding, don't allow propagating of pointer ORIG
+   that have a lower alignment than the DEST name.
+   This is to prevent losing alignment information from
+   __builtin_assume_aligned for expand (See also PR 122086).  */
+static bool
+forwprop_may_propagate_copy (tree dest, tree orig,
+                            bool dest_not_abnormal_phi_edge_p = false)
+{
+  if (!may_propagate_copy (dest, orig, dest_not_abnormal_phi_edge_p))
+    return false;
+
+  /* Only check alignment for the final folding.  */
+  if (!(cfun->curr_properties & PROP_last_full_fold))
+    return true;
+
+  /* Alignment only matters for pointer types.  */
+  if (!POINTER_TYPE_P (TREE_TYPE (dest)) || !POINTER_TYPE_P (TREE_TYPE (orig)))
+    return true;
+
+  unsigned aligndest = get_pointer_alignment (dest);
+  unsigned alignorig = get_pointer_alignment (orig);
+  return aligndest <= alignorig;
+}
+
 /* Set the lattice entry for NAME to VAL.  */
 static void
 fwprop_set_lattice_val (tree name, tree val)
@@ -5177,7 +5202,7 @@ pass_forwprop::execute (function *fun)
            }
          if (all_same)
            {
-             if (may_propagate_copy (res, first))
+             if (forwprop_may_propagate_copy (res, first))
                to_remove_defs.safe_push (SSA_NAME_VERSION (res));
              fwprop_set_lattice_val (res, first);
            }
@@ -5532,7 +5557,7 @@ pass_forwprop::execute (function *fun)
                {
                  if (!is_gimple_debug (stmt))
                    bitmap_set_bit (simple_dce_worklist, SSA_NAME_VERSION (use));
-                 if (may_propagate_copy (use, val))
+                 if (forwprop_may_propagate_copy (use, val))
                    {
                      propagate_value (usep, val);
                      substituted_p = true;
@@ -5695,7 +5720,7 @@ pass_forwprop::execute (function *fun)
                  /* If we can propagate the lattice-value mark the
                     stmt for removal.  */
                  if (val != lhs
-                     && may_propagate_copy (lhs, val))
+                     && forwprop_may_propagate_copy (lhs, val))
                    to_remove_defs.safe_push (SSA_NAME_VERSION (lhs));
                  fwprop_set_lattice_val (lhs, val);
                }
@@ -5717,7 +5742,7 @@ pass_forwprop::execute (function *fun)
              continue;
            tree val = fwprop_ssa_val (arg);
            if (val != arg
-               && may_propagate_copy (arg, val, !(e->flags & EDGE_ABNORMAL)))
+               && forwprop_may_propagate_copy (arg, val, !(e->flags & EDGE_ABNORMAL)))
              propagate_value (use_p, val);
          }