re PR tree-optimization/56051 (Wrong expression evaluation)

	PR tree-optimization/56051
	* fold-const.c (fold_binary_loc): Don't fold
	X < (cast) (1 << Y) into (X >> Y) != 0 if cast is either
	a narrowing conversion, or widening conversion from signed
	to unsigned.

	* gcc.c-torture/execute/pr56051.c: New test.

From-SVN: r195343

gcc/ChangeLog

+2013-01-21  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/56051
+	* fold-const.c (fold_binary_loc): Don't fold
+	X < (cast) (1 << Y) into (X >> Y) != 0 if cast is either
+	a narrowing conversion, or widening conversion from signed
+	to unsigned.
+
 2012-01-21  Uros Bizjak  <ubizjak@gmail.com>
 
 	PR rtl-optimization/56023

gcc/fold-const.c

@@ -13556,10 +13556,22 @@ fold_binary_loc (location_t loc,
 				   TREE_OPERAND (arg1, 1)),
 			   build_zero_cst (TREE_TYPE (arg0)));
 
+      /* Similarly for X < (cast) (1 << Y).  But cast can't be narrowing,
+	 otherwise Y might be >= # of bits in X's type and thus e.g.
+	 (unsigned char) (1 << Y) for Y 15 might be 0.
+	 If the cast is widening, then 1 << Y should have unsigned type,
+	 otherwise if Y is number of bits in the signed shift type minus 1,
+	 we can't optimize this.  E.g. (unsigned long long) (1 << Y) for Y
+	 31 might be 0xffffffff80000000.  */
       if ((code == LT_EXPR || code == GE_EXPR)
 	  && TYPE_UNSIGNED (TREE_TYPE (arg0))
 	  && CONVERT_EXPR_P (arg1)
 	  && TREE_CODE (TREE_OPERAND (arg1, 0)) == LSHIFT_EXPR
+	  && (TYPE_PRECISION (TREE_TYPE (arg1))
+	      >= TYPE_PRECISION (TREE_TYPE (TREE_OPERAND (arg1, 0))))
+	  && (TYPE_UNSIGNED (TREE_TYPE (TREE_OPERAND (arg1, 0)))
+	      || (TYPE_PRECISION (TREE_TYPE (arg1))
+		  == TYPE_PRECISION (TREE_TYPE (TREE_OPERAND (arg1, 0)))))
 	  && integer_onep (TREE_OPERAND (TREE_OPERAND (arg1, 0), 0)))
 	{
 	  tem = build2 (RSHIFT_EXPR, TREE_TYPE (arg0), arg0,

gcc/testsuite/ChangeLog

+2013-01-21  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/56051
+	* gcc.c-torture/execute/pr56051.c: New test.
+
 2012-01-21  Uros Bizjak  <ubizjak@gmail.com>
 
 	PR rtl-optimization/56023

gcc/testsuite/gcc.c-torture/execute/pr56051.c

+/* PR tree-optimization/56051 */
+
+extern void abort (void);
+
+int
+main ()
+{
+  unsigned char x1[1] = { 0 };
+  unsigned int s1 = __CHAR_BIT__;
+  int a1 = x1[0] < (unsigned char) (1 << s1);
+  unsigned char y1 = (unsigned char) (1 << s1);
+  int b1 = x1[0] < y1;
+  if (a1 != b1)
+    abort ();
+#if __SIZEOF_LONG_LONG__ > __SIZEOF_INT__
+  unsigned long long x2[1] = { 2ULL << (sizeof (int) * __CHAR_BIT__) };
+  unsigned int s2 = sizeof (int) * __CHAR_BIT__ - 1;
+  int a2 = x2[0] >= (unsigned long long) (1 << s2);
+  unsigned long long y2 = 1 << s2;
+  int b2 = x2[0] >= y2;
+  if (a2 != b2)
+    abort ();
+  unsigned long long x3[1] = { 2ULL << (sizeof (int) * __CHAR_BIT__) };
+  unsigned int s3 = sizeof (int) * __CHAR_BIT__ - 1;
+  int a3 = x3[0] >= (unsigned long long) (1U << s3);
+  unsigned long long y3 = 1U << s3;
+  int b3 = x3[0] >= y3;
+  if (a3 != b3)
+    abort ();
+#endif
+  return 0;
+}