[Sema] Add -Wpointer-compare

This patch adds a warning that diagnoses comparisons of pointers to
'\0'. This is often indicative of a bug (e.g. the user might've
forgotten to dereference the pointer).

Patch by Elaina Guan!

Differential Revision: https://reviews.llvm.org/D65595

llvm-svn: 367940

1 files changed, 49 insertions, 0 deletions

diff --git a/clang/test/Sema/warn-nullchar-nullptr.c b/clang/test/Sema/warn-nullchar-nullptr.c
new file mode 100644
index 00000000000..36a126a0433
--- /dev/null
+++ b/clang/test/Sema/warn-nullchar-nullptr.c
@@ -0,0 +1,49 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -Wall %s
+
+int test1(int *a) {
+  return a == '\0'; // expected-warning {{comparing a pointer to a null character constant; did you mean to compare to (void *)0?}}
+}
+
+int test2(int *a) {
+  return '\0' == a; // expected-warning {{comparing a pointer to a null character constant; did you mean to compare to (void *)0?}}
+}
+
+int test3(int *a) {
+  return a == L'\0'; // expected-warning {{comparing a pointer to a null character constant; did you mean to compare to (void *)0?}}
+}
+
+int test4(int *a) {
+  return a == u'\0'; // expected-warning {{comparing a pointer to a null character constant; did you mean to compare to (void *)0?}}
+}
+
+int test5(int *a) {
+  return a == U'\0'; // expected-warning {{comparing a pointer to a null character constant; did you mean to compare to (void *)0?}}
+}
+
+int test6(int *a) {
+  return a == (char)0; // expected-warning {{comparing a pointer to a null character constant; did you mean to compare to (void *)0?}}
+}
+
+typedef char my_char;
+int test7(int *a) {
+  return a == (my_char)0;
+  // expected-warning@-1 {{comparing a pointer to a null character constant; did you mean to compare to (void *)0?}}
+}
+
+int test8(int *a) {
+  return a != '\0'; // expected-warning {{comparing a pointer to a null character constant; did you mean to compare to (void *)0?}}
+}
+
+#define NULL (void *)0
+int test9(int *a) {
+  return a == '\0'; // expected-warning {{comparing a pointer to a null character constant; did you mean to compare to NULL?}}
+}
+
+#define MYCHAR char
+int test10(int *a) {
+  return a == (MYCHAR)0; // expected-warning {{comparing a pointer to a null character constant; did you mean to compare to NULL?}}
+}
+
+int test11(int *a) {
+  return a > '\0';
+}