re PR middle-end/52578 (Fails to fold another size difference)

2012-03-14  Richard Guenther  <rguenther@suse.de>

	PR middle-end/52578
	* fold-const.c (fold_unary_loc): Fold (T1)(T2)x to (T1)x if
	the outermost conversion is a sign-change only.
	(fold_binary_loc): Disregard widening and sign-changing
	conversions when we determine if two variables are equal
	for reassociation.
	* tree-ssa-forwprop.c (combine_conversions): Fold (T1)(T2)x to
	(T1)x if the outermost conversion is a sign-change only.

	* gcc.dg/pr52578.c: New testcase.

From-SVN: r185378

gcc/ChangeLog

+2012-03-14  Richard Guenther  <rguenther@suse.de>
+
+	PR middle-end/52578
+	* fold-const.c (fold_unary_loc): Fold (T1)(T2)x to (T1)x if
+	the outermost conversion is a sign-change only.
+	(fold_binary_loc): Disregard widening and sign-changing
+	conversions when we determine if two variables are equal
+	for reassociation.
+	* tree-ssa-forwprop.c (combine_conversions): Fold (T1)(T2)x to
+	(T1)x if the outermost conversion is a sign-change only.
+
 2012-03-14  Uros Bizjak  <ubizjak@gmail.com>
 
 	Revert:

gcc/fold-const.c

@@ -7843,10 +7843,13 @@ fold_unary_loc (location_t loc, enum tree_code code, tree type, tree op0)
 	    return fold_build1_loc (loc, code, type, TREE_OPERAND (op0, 0));
 
 	  /* If we have a sign-extension of a zero-extended value, we can
-	     replace that by a single zero-extension.  */
+	     replace that by a single zero-extension.  Likewise if the
+	     final conversion does not change precision we can drop the
+	     intermediate conversion.  */
 	  if (inside_int && inter_int && final_int
-	      && inside_prec < inter_prec && inter_prec < final_prec
-	      && inside_unsignedp && !inter_unsignedp)
+	      && ((inside_prec < inter_prec && inter_prec < final_prec
+		   && inside_unsignedp && !inter_unsignedp)
+		  || final_prec == inter_prec))
 	    return fold_build1_loc (loc, code, type, TREE_OPERAND (op0, 0));
 
 	  /* Two conversions in a row are not needed unless:
@@ -10335,10 +10338,21 @@ fold_binary_loc (location_t loc,
 
 		  if (TREE_CODE (tmp0) == NEGATE_EXPR)
 		    tmp0 = TREE_OPERAND (tmp0, 0);
+		  if (CONVERT_EXPR_P (tmp0)
+		      && INTEGRAL_TYPE_P (TREE_TYPE (TREE_OPERAND (tmp0, 0)))
+		      && (TYPE_PRECISION (TREE_TYPE (TREE_OPERAND (tmp0, 0)))
+			  <= TYPE_PRECISION (type)))
+		    tmp0 = TREE_OPERAND (tmp0, 0);
 		  if (TREE_CODE (tmp1) == NEGATE_EXPR)
 		    tmp1 = TREE_OPERAND (tmp1, 0);
+		  if (CONVERT_EXPR_P (tmp1)
+		      && INTEGRAL_TYPE_P (TREE_TYPE (TREE_OPERAND (tmp1, 0)))
+		      && (TYPE_PRECISION (TREE_TYPE (TREE_OPERAND (tmp1, 0)))
+			  <= TYPE_PRECISION (type)))
+		    tmp1 = TREE_OPERAND (tmp1, 0);
 		  /* The only case we can still associate with two variables
-		     is if they are the same, modulo negation.  */
+		     is if they are the same, modulo negation and bit-pattern
+		     preserving conversions.  */
 		  if (!operand_equal_p (tmp0, tmp1, 0))
 		    ok = false;
 		}

gcc/testsuite/ChangeLog

+2012-03-14  Richard Guenther  <rguenther@suse.de>
+
+	PR middle-end/52578
+	* gcc.dg/pr52578.c: New testcase.
+
 2012-03-14  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/52521

gcc/testsuite/gcc.dg/pr52578.c

+/* { dg-do compile } */
+/* { dg-options "-fdump-tree-original" } */
+
+long bar (long i)
+{
+  return (long)((unsigned long)i + 2) - (long)i;
+}
+long foo (int i)
+{
+  return (long)((unsigned long)i + 2) - (long)i;
+}
+
+/* { dg-final { scan-tree-dump-times "return 2;" 2 "original" } } */
+/* { dg-final { cleanup-tree-dump "original" } } */

gcc/tree-ssa-forwprop.c

@@ -2285,10 +2285,13 @@ combine_conversions (gimple_stmt_iterator *gsi)
 	}
 
       /* If we have a sign-extension of a zero-extended value, we can
-	 replace that by a single zero-extension.  */
+	 replace that by a single zero-extension.  Likewise if the
+	 final conversion does not change precision we can drop the
+	 intermediate conversion.  */
       if (inside_int && inter_int && final_int
-	  && inside_prec < inter_prec && inter_prec < final_prec
-	  && inside_unsignedp && !inter_unsignedp)
+	  && ((inside_prec < inter_prec && inter_prec < final_prec
+	       && inside_unsignedp && !inter_unsignedp)
+	      || final_prec == inter_prec))
 	{
 	  gimple_assign_set_rhs1 (stmt, defop0);
 	  update_stmt (stmt);