Hi all
in the Xcode 7.3.1 the following simple code
#include <iostream>
int main(int argc, const char * argv[]) {
size_t need_size = 0x1000000000000;
void *data = malloc(need_size);
if(data == NULL) {
std::cout << "data == NULL" << std::endl;
return 1;
} else {
std::cout << "data != NULL" << std::endl;
}
free(data);
return 0;
}
reports for the release build
data != NULL
Program ended with exit code: 0
which is clearly wrong, because right answer would be
data == NULL
Program ended with exit code: 1
g++ behaves correctly
recently I found out that we reported that problem to Apple
and we got an answer
""Engineering has determined that this issue behaves as intended based on the
following information:
The compiler "knows" how malloc works, and is allowed to optimize as if it
never fails.
We are now closing this bug report.”
clearly in my situation clang knows nothing :((
clang can’t optimize malloc here, because result of the malloc is used.
we have much more complex use case where
malloc was optimized out,
I just simplified the code
Note: -fno-builtin flag solve the problem
also if I use
std::cout << "data != NULL" << data << std::endl;
malloc wasn’t optimized
Dmitry Markman
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