reassoc vs uninitialized variable [PR112581]

Like r14-2293-g11350734240dba and r14-2289-gb083203f053f16,
reassociation can combine across a few bb and one of the usage
can be an uninitializated variable and if going from an conditional
usage to an unconditional usage can cause wrong code.
This uses maybe_undef_p like other passes where this can happen.

Note if-to-switch uses the function (init_range_entry) provided
by ressociation so we need to call mark_ssa_maybe_undefs there;
otherwise we assume almost all ssa names are uninitialized.

Bootstrapped and tested on x86_64-linux-gnu.

gcc/ChangeLog:

	PR tree-optimization/112581
	* gimple-if-to-switch.cc (pass_if_to_switch::execute): Call
	mark_ssa_maybe_undefs.
	* tree-ssa-reassoc.cc (can_reassociate_op_p): Uninitialized
	variables can not be reassociated.
	(init_range_entry): Check for uninitialized variables too.
	(init_reassoc): Call mark_ssa_maybe_undefs.

gcc/testsuite/ChangeLog:

	PR tree-optimization/112581
	* gcc.c-torture/execute/pr112581-1.c: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>

gcc/gimple-if-to-switch.cc

@@ -54,6 +54,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "alloc-pool.h"
 #include "tree-switch-conversion.h"
 #include "tree-ssa-reassoc.h"
+#include "tree-ssa.h"
 
 using namespace tree_switch_conversion;
 
@@ -494,6 +495,8 @@ pass_if_to_switch::execute (function *fun)
   auto_vec<if_chain *> all_candidates;
   hash_map<basic_block, condition_info *> conditions_in_bbs;
 
+  mark_ssa_maybe_undefs ();
+
   basic_block bb;
   FOR_EACH_BB_FN (bb, fun)
     find_conditions (bb, &conditions_in_bbs);

gcc/testsuite/gcc.c-torture/execute/pr112581-1.c

@@ -0,0 +1,37 @@
+/* { dg-require-effective-target int32plus } */
+/* PR tree-optimization/112581 */
+/* reassociation, used to combine 2 bb to together,
+   that made an unitialized variable unconditional used
+   which then at runtime would cause an infinite loop.  */
+int a = -1, b = 2501896061, c, d, e, f = 3, g;
+int main() {
+  unsigned h;
+  int i;
+  d = 0;
+  for (; d < 1; d++) {
+    int j = ~-((6UL ^ a) / b);
+    if (b)
+    L:
+      if (!f)
+        continue;
+    if (c)
+      i = 1;
+    if (j) {
+      i = 0;
+      while (e)
+        ;
+    }
+    g = -1 % b;
+    h = ~(b || h);
+    f = g || 0;
+    a = a || 0;
+    if (!a)
+      h = 0;
+    while (h > 4294967294)
+      if (i)
+        break;
+    if (c)
+      goto L;
+  }
+  return 0;
+}

gcc/tree-ssa-reassoc.cc

@@ -647,6 +647,9 @@ can_reassociate_op_p (tree op)
 {
   if (TREE_CODE (op) == SSA_NAME && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (op))
     return false;
+  /* Uninitialized variables can't participate in reassociation. */
+  if (TREE_CODE (op) == SSA_NAME && ssa_name_maybe_undef_p (op))
+    return false;
   /* Make sure asm goto outputs do not participate in reassociation since
      we have no way to find an insertion place after asm goto.  */
   if (TREE_CODE (op) == SSA_NAME
@@ -2600,7 +2603,8 @@ init_range_entry (struct range_entry *r, tree exp, gimple *stmt)
 	}
 
       if (TREE_CODE (arg0) != SSA_NAME
-	  || SSA_NAME_OCCURS_IN_ABNORMAL_PHI (arg0))
+	  || SSA_NAME_OCCURS_IN_ABNORMAL_PHI (arg0)
+	  || ssa_name_maybe_undef_p (arg0))
 	break;
       loc = gimple_location (stmt);
       switch (code)
@@ -7418,6 +7422,7 @@ init_reassoc (void)
   free (bbs);
   calculate_dominance_info (CDI_POST_DOMINATORS);
   plus_negates = vNULL;
+  mark_ssa_maybe_undefs ();
 }
 
 /* Cleanup after the reassociation pass, and print stats if