[analyzer] Assume that strings are no longer than SIZE_MAX/4.

This keeps the analyzer from making silly assumptions, like thinking
strlen(foo)+1 could wrap around to 0. This fixes PR16558.

Patch by Karthik Bhat!

llvm-svn: 188680

2 files changed, 36 insertions, 2 deletions

diff --git a/clang/test/Analysis/malloc.c b/clang/test/Analysis/malloc.c
index 83946c83a88..2e5213e3746 100644
--- a/clang/test/Analysis/malloc.c
+++ b/clang/test/Analysis/malloc.c
@@ -1216,6 +1216,38 @@ void testReallocEscaped(void **memory) {
   }
 }
 
+// PR16558
+void *smallocNoWarn(size_t size) {
+  if (size == 0) {
+    return malloc(1); // this branch is never called
+  } 
+  else {
+    return malloc(size);
+  }
+}
+
+char *dupstrNoWarn(const char *s) {
+  const int len = strlen(s);
+  char *p = (char*) smallocNoWarn(len + 1);
+  strcpy(p, s); // no-warning
+  return p;
+}
+
+void *smallocWarn(size_t size) {
+  if (size == 2) {
+    return malloc(1);
+  }
+  else {
+    return malloc(size);
+  }
+}
+
+char *dupstrWarn(const char *s) {
+  const int len = strlen(s);
+  char *p = (char*) smallocWarn(len + 1);
+  strcpy(p, s); // expected-warning{{String copy function overflows destination buffer}}
+  return p;
+}
 
 // ----------------------------------------------------------------------------
 // False negatives.
diff --git a/clang/test/Analysis/string.c b/clang/test/Analysis/string.c
index 6cf52f7a557..9fd3efb5c2d 100644
--- a/clang/test/Analysis/string.c
+++ b/clang/test/Analysis/string.c
@@ -430,11 +430,12 @@ void strcat_unknown_src_length(char *src, int offset) {
 // length for the "before" strlen, we won't be able to set one for "after".
 
 void strcat_too_big(char *dst, char *src) {
+  // We assume this can never actually happen, so we don't get a warning.
 	if (strlen(dst) != (((size_t)0) - 2))
 		return;
 	if (strlen(src) != 2)
 		return;
-	strcat(dst, src); // expected-warning{{This expression will create a string whose length is too big to be represented as a size_t}}
+	strcat(dst, src);
 }
 
 
@@ -653,11 +654,12 @@ void strncat_unknown_limit(float limit) {
 }
 
 void strncat_too_big(char *dst, char *src) {
+  // We assume this will never actually happen, so we don't get a warning.
   if (strlen(dst) != (((size_t)0) - 2))
     return;
   if (strlen(src) != 2)
     return;
-  strncat(dst, src, 2); // expected-warning{{This expression will create a string whose length is too big to be represented as a size_t}}
+  strncat(dst, src, 2);
 }
 
 void strncat_zero(char *src) {