[backport from gcc-4.8/trunk r190533 <mikpe@it.uu.se>]

gcc/

2012-08-20  Richard Earnshaw  <rearnsha@arm.com>

	PR tree-ssa/54295
	* tree-ssa-math-opts.c (widening_mult_conversion_strippable_p):
	New function.
	(is_widening_mult_rhs_p): Use it.

gcc/testsuite/

2012-08-20  Richard Earnshaw  <rearnsha@arm.com>

	PR tree-ssa/54295
	* gcc.c-torture/execute/20120817-1.c: New test.

--- gcc-4.7.1/gcc/testsuite/gcc.c-torture/execute/20120817-1.c.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.7.1/gcc/testsuite/gcc.c-torture/execute/20120817-1.c	2012-09-01 14:43:50.000000000 +0200
@@ -0,0 +1,14 @@
+typedef unsigned long long u64;
+unsigned long foo = 0;
+u64 f() __attribute__((noinline));
+
+u64 f() {
+  return ((u64)40) + ((u64) 24) * (int)(foo - 1);
+}
+
+int main ()
+{
+  if (f () != 16)
+    abort ();
+  exit (0);
+}
--- gcc-4.7.1/gcc/tree-ssa-math-opts.c.~1~	2011-12-20 22:33:48.000000000 +0100
+++ gcc-4.7.1/gcc/tree-ssa-math-opts.c	2012-09-01 14:43:50.000000000 +0200
@@ -1968,6 +1968,43 @@ struct gimple_opt_pass pass_optimize_bsw
  }
 };
 
+/* Return true if stmt is a type conversion operation that can be stripped
+   when used in a widening multiply operation.  */
+static bool
+widening_mult_conversion_strippable_p (tree result_type, gimple stmt)
+{
+  enum tree_code rhs_code = gimple_assign_rhs_code (stmt);
+
+  if (TREE_CODE (result_type) == INTEGER_TYPE)
+    {
+      tree op_type;
+      tree inner_op_type;
+
+      if (!CONVERT_EXPR_CODE_P (rhs_code))
+	return false;
+
+      op_type = TREE_TYPE (gimple_assign_lhs (stmt));
+
+      /* If the type of OP has the same precision as the result, then
+	 we can strip this conversion.  The multiply operation will be
+	 selected to create the correct extension as a by-product.  */
+      if (TYPE_PRECISION (result_type) == TYPE_PRECISION (op_type))
+	return true;
+
+      /* We can also strip a conversion if it preserves the signed-ness of
+	 the operation and doesn't narrow the range.  */
+      inner_op_type = TREE_TYPE (gimple_assign_rhs1 (stmt));
+
+      if (TYPE_UNSIGNED (op_type) == TYPE_UNSIGNED (inner_op_type)
+	  && TYPE_PRECISION (op_type) > TYPE_PRECISION (inner_op_type))
+	return true;
+
+      return false;
+    }
+
+  return rhs_code == FIXED_CONVERT_EXPR;
+}
+
 /* Return true if RHS is a suitable operand for a widening multiplication,
    assuming a target type of TYPE.
    There are two cases:
@@ -1992,9 +2029,7 @@ is_widening_mult_rhs_p (tree type, tree 
       if (is_gimple_assign (stmt))
 	{
 	  rhs_code = gimple_assign_rhs_code (stmt);
-	  if (TREE_CODE (type) == INTEGER_TYPE
-	      ? !CONVERT_EXPR_CODE_P (rhs_code)
-	      : rhs_code != FIXED_CONVERT_EXPR)
+	  if (! widening_mult_conversion_strippable_p (type, stmt))
 	    rhs1 = rhs;
 	  else
 	    {