[llvm-bugs] [Bug 44424] New: Simple C program produces different output if compiled with -O1 instead of -O0

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=44424

            Bug ID: 44424
           Summary: Simple C program produces different output if compiled
                    with -O1 instead of -O0
           Product: clang
           Version: unspecified
          Hardware: Macintosh
                OS: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: dirk.hoffmann at me.com
                CC: blitzrakete at gmail.com, dgregor at apple.com,
                    erik.pilkington at gmail.com, llvm-bugs at lists.llvm.org,
                    richard-llvm at metafoo.co.uk

Test program: main.cpp


#include <stdint.h>
#include <stdio.h>

bool foo(uint32_t x, uint32_t y)
{
        uint32_t z = (uint16_t)x * (uint16_t)y;
        return z & 0x80000000;
}

int main(int argc, char *argv[])
{
        printf("%d\n", foo(0x7FFFF, 0x7FFFF));
}



Compiler: 

Apple clang version 11.0.0 (clang-1100.0.33.8)
Target: x86_64-apple-darwin18.7.0
Thread model: posix

Output:

> clang -O0 main.cpp; ./a.out 
1

> clang -O1 main.cpp; ./a.out 
0

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20200101/75b0462a/attachment.html>