re PR middle-end/58742 (pointer arithmetic simplification)

2014-01-28  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/58742
	* tree-ssa-forwprop.c (associate_plusminus): Handle
	pointer subtraction of the form (T)(P + A) - (T)P.

From-SVN: r207194

gcc/ChangeLog

+2014-01-28  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/58742
+	* tree-ssa-forwprop.c (associate_plusminus): Handle
+	pointer subtraction of the form (T)(P + A) - (T)P.
+
 2014-01-28  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
 
 	* config/arm/arm.c (arm_new_rtx_costs): Remove useless statement

gcc/tree-ssa-forwprop.c

@@ -2543,6 +2543,7 @@ associate_plusminus (gimple_stmt_iterator *gsi)
 	CST +- (CST +- A)  ->  CST +- A
 	CST +- (A +- CST)  ->  CST +- A
 	A + ~A             ->  -1
+	(T)(P + A) - (T)P  -> (T)A
 
      via commutating the addition and contracting operations to zero
      by reassociation.  */
@@ -2646,6 +2647,55 @@ associate_plusminus (gimple_stmt_iterator *gsi)
 		  gimple_set_modified (stmt, true);
 		}
 	    }
+	  else if (CONVERT_EXPR_CODE_P (def_code) && code == MINUS_EXPR
+		   && TREE_CODE (rhs2) == SSA_NAME)
+	    {
+	      /* (T)(ptr + adj) - (T)ptr -> (T)adj.  */
+	      gimple def_stmt2 = SSA_NAME_DEF_STMT (rhs2);
+	      if (TREE_CODE (gimple_assign_rhs1 (def_stmt)) == SSA_NAME
+		  && is_gimple_assign (def_stmt2)
+		  && can_propagate_from (def_stmt2)
+		  && CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (def_stmt2))
+		  && TREE_CODE (gimple_assign_rhs1 (def_stmt2)) == SSA_NAME)
+		{
+		  /* Now we have (T)A - (T)ptr.  */
+		  tree ptr = gimple_assign_rhs1 (def_stmt2);
+		  def_stmt2 = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (def_stmt));
+		  if (is_gimple_assign (def_stmt2)
+		      && gimple_assign_rhs_code (def_stmt2) == POINTER_PLUS_EXPR
+		      && gimple_assign_rhs1 (def_stmt2) == ptr)
+		    {
+		      /* And finally (T)(ptr + X) - (T)ptr.  */
+		      tree adj = gimple_assign_rhs2 (def_stmt2);
+		      /* If the conversion of the pointer adjustment to the
+		         final type requires a sign- or zero-extension we
+			 have to punt - it is not defined which one is
+			 correct.  */
+		      if (TYPE_PRECISION (TREE_TYPE (rhs1))
+			  <= TYPE_PRECISION (TREE_TYPE (adj))
+			  || (TREE_CODE (adj) == INTEGER_CST
+			      && tree_int_cst_sign_bit (adj) == 0))
+			{
+			  if (useless_type_conversion_p (TREE_TYPE (rhs1),
+							 TREE_TYPE (adj)))
+			    {
+			      code = TREE_CODE (adj);
+			      rhs1 = adj;
+			    }
+			  else
+			    {
+			      code = NOP_EXPR;
+			      rhs1 = adj;
+			    }
+			  rhs2 = NULL_TREE;
+			  gimple_assign_set_rhs_with_ops (gsi, code, rhs1,
+							  NULL_TREE);
+			  gcc_assert (gsi_stmt (*gsi) == stmt);
+			  gimple_set_modified (stmt, true);
+			}
+		    }
+		}
+	    }
 	}
     }