[backport gcc-4.8/r194444, fixes PR55481 regression from PR53676 patch <mikpe@it.uu.se>]

Date: Wed, 12 Dec 2012 14:03:36 +0100 (CET)
From: Richard Biener <rguenther at suse dot de>
Subject: [PATCH] Fix PR55481
List-Archive: <http://gcc.gnu.org/ml/gcc-patches/>

This patch from Zdenek removes special code handling the forced
rewrite of the original BIV definition.  The code was broken,
so simply fallback to the general rewriting code which works fine.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk
(the issue is latent on the branches).

Thanks Zdenek for the fix,
Richard.

gcc/

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/testsuite/

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

	PR tree-optimization/55481
	* gcc.dg/torture/pr55481.c: New testcase.

--- gcc-4.7.2/gcc/testsuite/gcc.dg/torture/pr55481.c.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.7.2/gcc/testsuite/gcc.dg/torture/pr55481.c	2012-12-23 12:33:41.000000000 +0100
@@ -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;
+}
--- gcc-4.7.2/gcc/tree-ssa-loop-ivopts.c.~1~	2012-02-06 14:43:03.000000000 +0100
+++ gcc-4.7.2/gcc/tree-ssa-loop-ivopts.c	2012-12-23 12:33:41.000000000 +0100
@@ -6170,35 +6170,24 @@ rewrite_use_nonlinear_expr (struct ivopt
   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;
@@ -6206,24 +6195,13 @@ rewrite_use_nonlinear_expr (struct ivopt
       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: