libcpp: Fix unsigned promotion for unevaluated divide by zero [PR112701]

When libcpp encounters a divide by zero while processing a constant
expression "x/y", it returns "x" as a fallback. The value of the fallback is
not normally important, since an error will be generated anyway, but if the
expression appears in an unevaluated context, such as "0 ? 0/0u : -1", then
there will be no error, and the fallback value will be meaningful to the
extent that it may cause promotion from signed to unsigned of an operand
encountered later. As the PR notes, libcpp does not do the unsigned
promotion correctly in this case; fix it by making the fallback return value
unsigned as necessary.

libcpp/ChangeLog:

	PR preprocessor/112701
	* expr.cc (num_div_op): Set unsignedp appropriately when returning a
	stub value for divide by 0.

gcc/testsuite/ChangeLog:

	PR preprocessor/112701
	* gcc.dg/cpp/expr.c: Add additional tests to cover divide by 0 in an
	unevaluated context, where the unsignedness still matters.

diff --git a/gcc/testsuite/gcc.dg/cpp/expr.c b/gcc/testsuite/gcc.dg/cpp/expr.c
index 532bd6812378b9c29874baacdc3c9e61aadcded1..055e17ae753a8421d451c1a149d8f19e8e3f7b08 100644 (file)
--- a/gcc/testsuite/gcc.dg/cpp/expr.c
+++ b/gcc/testsuite/gcc.dg/cpp/expr.c
@@ -1,6 +1,7 @@
 /* Copyright (C) 2000, 2001 Free Software Foundation, Inc.  */
 
 /* { dg-do preprocess } */
+/* { dg-additional-options "-Wall" } */
 
 /* Test we get signedness of ?: operator correct.  We would skip
    evaluation of one argument, and might therefore not transfer its
@@ -8,10 +9,27 @@
 
 /* Neil Booth, 19 Jul 2002.  */
 
-#if (1 ? -2: 0 + 1U) < 0
+#if (1 ? -2: 0 + 1U) < 0 /* { dg-warning {the left operand of ":" changes sign} } */
 #error                         /* { dg-bogus "error" } */
 #endif
 
-#if (0 ? 0 + 1U: -2) < 0
+#if (0 ? 0 + 1U: -2) < 0 /* { dg-warning {the right operand of ":" changes sign} } */
 #error                         /* { dg-bogus "error" } */
 #endif
+
+/* PR preprocessor/112701 */
+#if (0 ? 0/0u : -1) < 0 /* { dg-warning {the right operand of ":" changes sign} } */
+#error /* { dg-bogus "error" } */
+#endif
+
+#if (0 ? 0u/0 : -1) < 0 /* { dg-warning {the right operand of ":" changes sign} } */
+#error /* { dg-bogus "error" } */
+#endif
+
+#if (1 ? -1 : 0/0u) < 0 /* { dg-warning {the left operand of ":" changes sign} } */
+#error /* { dg-bogus "error" } */
+#endif
+
+#if (1 ? -1 : 0u/0) < 0 /* { dg-warning {the left operand of ":" changes sign} } */
+#error /* { dg-bogus "error" } */
+#endif

diff --git a/libcpp/expr.cc b/libcpp/expr.cc
index 825d2c2369da906993cd65bfbde375ef270f13c4..4f4a9722ac7047c681b6cf74df82269be7db10bc 100644 (file)
--- a/libcpp/expr.cc
+++ b/libcpp/expr.cc
@@ -2216,6 +2216,7 @@ num_div_op (cpp_reader *pfile, cpp_num lhs, cpp_num rhs, enum cpp_ttype op,
       if (!pfile->state.skip_eval)
        cpp_error_with_line (pfile, CPP_DL_ERROR, location, 0,
                             "division by zero in #if");
+      lhs.unsignedp = unsignedp;
       return lhs;
     }