re PR middle-end/55481 (-O2 generates a wrong-code infinite loop in C++Benchmark's simple_types_constant_folding int8 xor test)

2012-12-12  Zdenek Dvorak  <ook@ucw.cz>

	PR tree-optimization/55481
	* tree-ssa-loop-ivopts.c (rewrite_use_nonlinear_expr): Fall
	back to general rewriting if we cannot leave an original biv
	definition alone.

	* gcc.dg/torture/pr55481.c: New testcase.

From-SVN: r194444

4 files changed, 38 insertions, 32 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 334a3ca..d9630ed 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2012-12-12  Zdenek Dvorak  <ook@ucw.cz>
+
+	PR tree-optimization/55481
+	* tree-ssa-loop-ivopts.c (rewrite_use_nonlinear_expr): Fall
+	back to general rewriting if we cannot leave an original biv
+	definition alone.
+
 2012-12-12  Jakub Jelinek  <jakub@redhat.com>
 
 	PR target/55659
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index f9a68a5..35e21d6 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2012-12-12  Zdenek Dvorak  <ook@ucw.cz>
+
+	PR tree-optimization/55481
+	* gcc.dg/torture/pr55481.c: New testcase.
+
 2012-12-12  Steven Bosscher  <steven@gcc.gnu.org>
 	    Jakub Jelinek  <jakub@redhat.com>
 
diff --git a/gcc/testsuite/gcc.dg/torture/pr55481.c b/gcc/testsuite/gcc.dg/torture/pr55481.c
new file mode 100644
index 0000000..26ba9ff
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr55481.c
@@ -0,0 +1,16 @@
+/* { dg-do run } */
+
+int main()
+{
+  signed char result = 0;
+  int n;
+  for (n = 0; n < 13; ++n)
+    {
+      int tem = result;
+      tem = tem + 31;
+      result = tem;
+    }
+  if (result != -109)
+    __builtin_abort ();
+  return 0;
+}
diff --git a/gcc/tree-ssa-loop-ivopts.c b/gcc/tree-ssa-loop-ivopts.c
index 1e41fa9..c33fc7c 100644
--- a/gcc/tree-ssa-loop-ivopts.c
+++ b/gcc/tree-ssa-loop-ivopts.c
@@ -6088,35 +6088,24 @@ rewrite_use_nonlinear_expr (struct ivopts_data *data,
   if (cand->pos == IP_ORIGINAL
       && cand->incremented_at == use->stmt)
     {
-      tree step, ctype, utype;
-      enum tree_code incr_code = PLUS_EXPR, old_code;
+      enum tree_code stmt_code;
 
       gcc_assert (is_gimple_assign (use->stmt));
       gcc_assert (gimple_assign_lhs (use->stmt) == cand->var_after);
 
-      step = cand->iv->step;
-      ctype = TREE_TYPE (step);
-      utype = TREE_TYPE (cand->var_after);
-      if (TREE_CODE (step) == NEGATE_EXPR)
-	{
-	  incr_code = MINUS_EXPR;
-	  step = TREE_OPERAND (step, 0);
-	}
-
       /* Check whether we may leave the computation unchanged.
 	 This is the case only if it does not rely on other
 	 computations in the loop -- otherwise, the computation
 	 we rely upon may be removed in remove_unused_ivs,
 	 thus leading to ICE.  */
-      old_code = gimple_assign_rhs_code (use->stmt);
-      if (old_code == PLUS_EXPR
-	  || old_code == MINUS_EXPR
-	  || old_code == POINTER_PLUS_EXPR)
+      stmt_code = gimple_assign_rhs_code (use->stmt);
+      if (stmt_code == PLUS_EXPR
+	  || stmt_code == MINUS_EXPR
+	  || stmt_code == POINTER_PLUS_EXPR)
 	{
 	  if (gimple_assign_rhs1 (use->stmt) == cand->var_before)
 	    op = gimple_assign_rhs2 (use->stmt);
-	  else if (old_code != MINUS_EXPR
-		   && gimple_assign_rhs2 (use->stmt) == cand->var_before)
+	  else if (gimple_assign_rhs2 (use->stmt) == cand->var_before)
 	    op = gimple_assign_rhs1 (use->stmt);
 	  else
 	    op = NULL_TREE;
@@ -6124,24 +6113,13 @@ rewrite_use_nonlinear_expr (struct ivopts_data *data,
       else
 	op = NULL_TREE;
 
-      if (op
-	  && (TREE_CODE (op) == INTEGER_CST
-	      || operand_equal_p (op, step, 0)))
+      if (op && expr_invariant_in_loop_p (data->current_loop, op))
 	return;
-
-      /* Otherwise, add the necessary computations to express
-	 the iv.  */
-      op = fold_convert (ctype, cand->var_before);
-      comp = fold_convert (utype,
-			   build2 (incr_code, ctype, op,
-				   unshare_expr (step)));
-    }
-  else
-    {
-      comp = get_computation (data->current_loop, use, cand);
-      gcc_assert (comp != NULL_TREE);
     }
 
+  comp = get_computation (data->current_loop, use, cand);
+  gcc_assert (comp != NULL_TREE);
+
   switch (gimple_code (use->stmt))
     {
     case GIMPLE_PHI: