re PR preprocessor/55715 (bogus overflow warning for #if A-B when A<0 & B==minimum integer)

	PR preprocessor/55715
libcpp:
	* expr.c (num_binary_op): Implement subtraction directly rather
	than with negation and falling through into addition case.

gcc/testsuite:
	* gcc.dg/cpp/expr-overflow-1.c: New test.

From-SVN: r205846

gcc/testsuite/ChangeLog

+2013-12-09  Joseph Myers  <joseph@codesourcery.com>
+
+	PR preprocessor/55715
+	* gcc.dg/cpp/expr-overflow-1.c: New test.
+
 2013-12-10  Tobias Burnus  <burnus@net-b.de>
 
 	PR fortran/59428

gcc/testsuite/gcc.dg/cpp/expr-overflow-1.c

+/* Test overflow in preprocessor arithmetic.  PR 55715.  */
+/* { dg-do preprocess } */
+/* { dg-options "-std=c99" } */
+
+#include <stdint.h>
+
+#if -1 - INTMAX_MIN
+#endif
+
+#if 0 - INTMAX_MIN /* { dg-warning "overflow" } */
+#endif
+
+#if 1 * INTMAX_MIN
+#endif
+
+#if -1 * INTMAX_MIN /* { dg-warning "overflow" } */
+#endif
+
+#if 0 * INTMAX_MIN
+#endif
+
+#if -INTMAX_MIN /* { dg-warning "overflow" } */
+#endif
+
+#if +INTMAX_MIN
+#endif
+
+#if INTMAX_MIN / 1
+#endif
+
+#if INTMAX_MIN / -1 /* { dg-warning "overflow" } */
+#endif
+
+#if UINTMAX_MAX * UINTMAX_MAX
+#endif
+
+#if UINTMAX_MAX / -1
+#endif
+
+#if UINTMAX_MAX + INTMAX_MAX
+#endif
+
+#if UINTMAX_MAX - INTMAX_MIN
+#endif

libcpp/ChangeLog

+2013-12-09  Joseph Myers  <joseph@codesourcery.com>
+
+	PR preprocessor/55715
+	* expr.c (num_binary_op): Implement subtraction directly rather
+	than with negation and falling through into addition case.
+
 2013-11-18  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
 
 	* lex.c (search_line_fast): Correct for little endian.

libcpp/expr.c

@@ -1836,7 +1836,22 @@ num_binary_op (cpp_reader *pfile, cpp_num lhs, cpp_num rhs, enum cpp_ttype op)
 
       /* Arithmetic.  */
     case CPP_MINUS:
-      rhs = num_negate (rhs, precision);
+      result.low = lhs.low - rhs.low;
+      result.high = lhs.high - rhs.high;
+      if (result.low > lhs.low)
+	result.high--;
+      result.unsignedp = lhs.unsignedp || rhs.unsignedp;
+      result.overflow = false;
+
+      result = num_trim (result, precision);
+      if (!result.unsignedp)
+	{
+	  bool lhsp = num_positive (lhs, precision);
+	  result.overflow = (lhsp != num_positive (rhs, precision)
+			     && lhsp != num_positive (result, precision));
+	}
+      return result;
+
     case CPP_PLUS:
       result.low = lhs.low + rhs.low;
       result.high = lhs.high + rhs.high;