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 --git a/gcc/testsuite/gcc.dg/torture/pr109002.c b/gcc/testsuite/gcc.dg/torture/pr109002.c
new file mode 100644 (file)
index 0000000..5575a4b
--- /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 f77732d..37cad36 100644 (file)
--- 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));
+               }
            }
        }
     }