[cfe-dev] no warning with returns_nonnull

Xavier Chantry via cfe-dev cfe-dev at lists.llvm.org
Mon Dec 7 06:47:56 PST 2015

clang 3.6 brought some very useful warnings when a function argument 
with __attribute__((nonnull)) had a NULL check:
warning: nonnull parameter 'p' will evaluate to 'true' on first 
encounter [-Wpointer-bool-conversion]

With gcc and earlier clang versions, the NULL check was silently 
optimized away.

We just realized that the same problem remains with 
__attribute__((returns_nonnull)): NULL checks are silently optimized 
away, as in the following test case.

int *nul(void) {
     return NULL;

__attribute__((returns_nonnull)) int *foo(void)
     return nul();

int main(void)
     fprintf(stderr, "%p\n", foo());
     if (foo() == NULL) {
         fprintf(stderr, "foo is null\n");
     return 0;

Is it planned to have a warning in that case ?

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