re PR c/65179 (Introduce new C warning: -Wshift-negative-value)

	PR c/65179
	* c-common.c (c_fully_fold_internal): Warn when left shifting a
	negative value.
	* c.opt (Wshift-negative-value): New option.
	* c-opts.c (c_common_post_options): Set warn_shift_negative_value
	when -Wextra and C99/C++11 mode.

	* c-typeck.c (build_binary_op): Warn when left shifting a negative
	value.

	* typeck.c (cp_build_binary_op): Warn when left shifting a negative
	value.

	* doc/invoke.texi: Document -Wshift-negative-value.

	* c-c++-common/Wshift-negative-value-1.c: New test.
	* testsuite/c-c++-common/Wshift-negative-value-2.c: New test.
	* testsuite/c-c++-common/Wshift-negative-value-3.c: New test.
	* testsuite/c-c++-common/Wshift-negative-value-4.c: New test.
	* testsuite/c-c++-common/Wshift-negative-value-5.c: New test.
	* testsuite/c-c++-common/Wshift-negative-value-6.c: New test.
	* testsuite/gcc.dg/c90-left-shift-1.c: New test.
	* testsuite/gcc.dg/c99-const-expr-7.c: Add dg-error.
	* testsuite/gcc.dg/c99-left-shift-1.c: New test.

From-SVN: r222889

1 files changed, 49 insertions, 0 deletions

diff --git a/gcc/testsuite/c-c++-common/Wshift-negative-value-2.c b/gcc/testsuite/c-c++-common/Wshift-negative-value-2.c
new file mode 100644
index 0000000..fc89af1
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wshift-negative-value-2.c
@@ -0,0 +1,49 @@
+/* PR c/65179 */
+/* { dg-do compile } */
+/* { dg-options "-O -Wshift-negative-value" } */
+/* { dg-additional-options "-std=c++11" { target c++ } } */
+
+enum E {
+  A = 0 << 1,
+  B = 1 << 1,
+  C = -1 << 1, /* { dg-warning "left shift of negative value" } */
+  D = 0 >> 1,
+  E = 1 >> 1,
+  F = -1 >> 1
+};
+
+int
+left (int x)
+{
+  /* Warn for LSHIFT_EXPR.  */
+  const int z = 0;
+  const int o = 1;
+  const int m = -1;
+  int r = 0;
+  r += z << x;
+  r += o << x;
+  r += m << x; /* { dg-warning "left shift of negative value" } */
+  r += 0 << x;
+  r += 1 << x;
+  r += -1 << x; /* { dg-warning "left shift of negative value" } */
+  r += -1U << x;
+  return r;
+}
+
+int
+right (int x)
+{
+  /* Shouldn't warn for RSHIFT_EXPR.  */
+  const int z = 0;
+  const int o = 1;
+  const int m = -1;
+  int r = 0;
+  r += z >> x;
+  r += o >> x;
+  r += m >> x;
+  r += 0 >> x;
+  r += 1 >> x;
+  r += -1 >> x;
+  r += -1U >> x;
+  return r;
+}