[analyzer] strncpy: Special-case a length of 0 to avoid an incorrect warning.

We check the address of the last element accessed, but with 0 calculating that
address results in element -1. This patch bails out early (and avoids a bunch
of other work at that).

Fixes PR12807.

llvm-svn: 156769

1 files changed, 22 insertions, 0 deletions

diff --git a/clang/test/Analysis/string.c b/clang/test/Analysis/string.c
index 24e29ebb02b..dc38681b35b 100644
--- a/clang/test/Analysis/string.c
+++ b/clang/test/Analysis/string.c
@@ -578,6 +578,17 @@ void strncpy_exactly_matching_buffer2(char *y) {
 		(void)*(int*)0; // no-warning
 }
 
+void strncpy_zero(char *src) {
+  char dst[] = "123";
+  strncpy(dst, src, 0); // no-warning
+}
+
+void strncpy_empty() {
+  char dst[] = "123";
+  char src[] = "";
+  strncpy(dst, src, 4); // no-warning
+}
+
 //===----------------------------------------------------------------------===
 // strncat()
 //===----------------------------------------------------------------------===
@@ -716,6 +727,17 @@ void strncat_too_big(char *dst, char *src) {
   strncat(dst, src, 2); // expected-warning{{This expression will create a string whose length is too big to be represented as a size_t}}
 }
 
+void strncat_zero(char *src) {
+  char dst[] = "123";
+  strncat(dst, src, 0); // no-warning
+}
+
+void strncat_empty() {
+  char dst[8] = "123";
+  char src[] = "";
+  strncat(dst, src, 4); // no-warning
+}
+
 //===----------------------------------------------------------------------===
 // strcmp()
 //===----------------------------------------------------------------------===