[gcc r13-6443] tree-optimization/109002 - partial PRE miscompilation

[gcc r13-6443] tree-optimization/109002 - partial PRE miscompilation

[Richard Biener]

https://gcc.gnu.org/g:0132acc03cada2c3b47c48a205e821563153fc80

commit r13-6443-g0132acc03cada2c3b47c48a205e821563153fc80
Author: Richard Biener <rguenther@suse.de>
Date:   Fri Mar 3 10:41:29 2023 +0100

    tree-optimization/109002 - partial PRE miscompilation
    
    Partial PRE ends up miscompiling the testcase in PR109002, likely
    involving a corner case when inifinite loops are involved.  The
    following avoids the miscompilation by addressing a long-standing
    oddity that manifests in odd partial partial redundancies eliminated
    that are full redundancies.  The oddity is that while we properly
    PHI translate the PA_IN set from the successors when computing
    PA_OUT but we fail to do the same for ANTIC_IN which is supposed
    to be unioned.  That results in expressions with wrong virtual
    operands being placed in the PA_OUT/IN sets and the pruning
    machinery to go wrong because it assumes the expressions in the
    sets have virtual operands that are valid in the respective blocks.
    
            PR tree-optimization/109002
            * tree-ssa-pre.cc (compute_partial_antic_aux): Properly
            PHI-translate ANTIC_IN.
    
            * gcc.dg/torture/pr109002.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/torture/pr109002.c | 27 +++++++++++++++++++++++++++
 gcc/tree-ssa-pre.cc                     | 20 ++++++++++++++------
 2 files changed, 41 insertions(+), 6 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/torture/pr109002.c b/gcc/testsuite/gcc.dg/torture/pr109002.c
new file mode 100644
index 00000000000..5575a4b9edc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr109002.c
@@ -0,0 +1,27 @@
+/* { dg-do run } */
+/* { dg-additional-options "-ftree-pre -ftree-partial-pre" } */
+
+extern void exit (int);
+
+int g;
+int h;
+
+void __attribute__((noipa)) bar ()
+{
+  if (g)
+    exit (0);
+}
+
+int main(void)
+{
+  for (int i = 0; ; i++) {
+      for (int j = 0; j < g; j++);
+      if (i & 1) {
+	  if (h)
+	    continue;
+	  if (g)
+	    bar ();
+	  g = 1;
+      }
+  }
+}
diff --git a/gcc/tree-ssa-pre.cc b/gcc/tree-ssa-pre.cc
index f77732d75c3..37cad36f2de 100644
--- a/gcc/tree-ssa-pre.cc
+++ b/gcc/tree-ssa-pre.cc
@@ -2364,11 +2364,14 @@ compute_partial_antic_aux (basic_block block,
 	      unsigned int i;
 	      bitmap_iterator bi;
 
-	      FOR_EACH_EXPR_ID_IN_SET (ANTIC_IN (e->dest), i, bi)
-		bitmap_value_insert_into_set (PA_OUT,
-					      expression_for_id (i));
 	      if (!gimple_seq_empty_p (phi_nodes (e->dest)))
 		{
+		  bitmap_set_t antic_in = bitmap_set_new ();
+		  phi_translate_set (antic_in, ANTIC_IN (e->dest), e);
+		  FOR_EACH_EXPR_ID_IN_SET (antic_in, i, bi)
+		    bitmap_value_insert_into_set (PA_OUT,
+						  expression_for_id (i));
+		  bitmap_set_free (antic_in);
 		  bitmap_set_t pa_in = bitmap_set_new ();
 		  phi_translate_set (pa_in, PA_IN (e->dest), e);
 		  FOR_EACH_EXPR_ID_IN_SET (pa_in, i, bi)
@@ -2377,9 +2380,14 @@ compute_partial_antic_aux (basic_block block,
 		  bitmap_set_free (pa_in);
 		}
 	      else
-		FOR_EACH_EXPR_ID_IN_SET (PA_IN (e->dest), i, bi)
-		  bitmap_value_insert_into_set (PA_OUT,
-						expression_for_id (i));
+		{
+		  FOR_EACH_EXPR_ID_IN_SET (ANTIC_IN (e->dest), i, bi)
+		    bitmap_value_insert_into_set (PA_OUT,
+						  expression_for_id (i));
+		  FOR_EACH_EXPR_ID_IN_SET (PA_IN (e->dest), i, bi)
+		    bitmap_value_insert_into_set (PA_OUT,
+						  expression_for_id (i));
+		}
 	    }
 	}
     }