[backport from gcc-4.7/trunk <mikpe@it.uu.se>]

gcc/

2011-03-20  Jakub Jelinek  <jakub@redhat.com>

	PR c/42544
	PR c/48197
	* c-common.c (shorten_compare): If primopN is first sign-extended
	to opN and then zero-extended to result type, set primopN to opN.

gcc/testsuite/

2011-03-20  Jakub Jelinek  <jakub@redhat.com>

	PR c/42544
	PR c/48197
	* gcc.c-torture/execute/pr42544.c: New test.
	* gcc.c-torture/execute/pr48197.c: New test.

--- gcc-4.6-20110318/gcc/c-family/c-common.c.~1~	2011-03-11 23:38:58.000000000 +0100
+++ gcc-4.6-20110318/gcc/c-family/c-common.c	2011-03-21 19:58:56.000000000 +0100
@@ -3300,6 +3300,20 @@ shorten_compare (tree *op0_ptr, tree *op
   primop0 = get_narrower (op0, &unsignedp0);
   primop1 = get_narrower (op1, &unsignedp1);
 
+  /* If primopN is first sign-extended from primopN's precision to opN's
+     precision, then zero-extended from opN's precision to
+     *restype_ptr precision, shortenings might be invalid.  */
+  if (TYPE_PRECISION (TREE_TYPE (primop0)) < TYPE_PRECISION (TREE_TYPE (op0))
+      && TYPE_PRECISION (TREE_TYPE (op0)) < TYPE_PRECISION (*restype_ptr)
+      && !unsignedp0
+      && TYPE_UNSIGNED (TREE_TYPE (op0)))
+    primop0 = op0;
+  if (TYPE_PRECISION (TREE_TYPE (primop1)) < TYPE_PRECISION (TREE_TYPE (op1))
+      && TYPE_PRECISION (TREE_TYPE (op1)) < TYPE_PRECISION (*restype_ptr)
+      && !unsignedp1
+      && TYPE_UNSIGNED (TREE_TYPE (op1)))
+    primop1 = op1;
+
   /* Handle the case that OP0 does not *contain* a conversion
      but it *requires* conversion to FINAL_TYPE.  */
 
--- gcc-4.6-20110318/gcc/testsuite/gcc.c-torture/execute/pr42544.c.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.6-20110318/gcc/testsuite/gcc.c-torture/execute/pr42544.c	2011-03-21 19:58:56.000000000 +0100
@@ -0,0 +1,14 @@
+/* PR c/42544 */
+
+extern void abort (void);
+
+int
+main ()
+{
+  signed short s = -1;
+  if (sizeof (long long) == sizeof (unsigned int))
+    return 0;
+  if ((unsigned int) s >= 0x100000000ULL)
+    abort ();
+  return 0;
+}
--- gcc-4.6-20110318/gcc/testsuite/gcc.c-torture/execute/pr48197.c.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.6-20110318/gcc/testsuite/gcc.c-torture/execute/pr48197.c	2011-03-21 19:58:56.000000000 +0100
@@ -0,0 +1,25 @@
+/* PR c/48197 */
+
+extern void abort (void);
+static int y = 0x8000;
+
+int
+main ()
+{
+  unsigned int x = (short)y;
+  if (sizeof (0LL) == sizeof (0U))
+    return 0;
+  if (0LL > (0U ^ (short)-0x8000))
+    abort ();
+  if (0LL > (0U ^ x))
+    abort ();
+  if (0LL > (0U ^ (short)y))
+    abort ();
+  if ((0U ^ (short)-0x8000) < 0LL)
+    abort ();
+  if ((0U ^ x) < 0LL)
+    abort ();
+  if ((0U ^ (short)y) < 0LL)
+    abort ();
+  return 0;
+}