[llvm-bugs] [Bug 36463] New: Wrong constant folding

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=36463

            Bug ID: 36463
           Summary: Wrong constant folding
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: ishiura-compiler at ml.kwansei.ac.jp
                CC: llvm-bugs at lists.llvm.org

LLVM + clang 7.0 for x86_64 miscompiles the following code.

% cat test.c
short a = 0;
int main (void)
{
  volatile int b = 0;
  volatile int c = 0x102;
  int d = (unsigned char)((a^0x101)^(0x101%c))+b;
  if (d != 0)  __builtin_abort();
  return 0;
}

% clang-7.0 -O1 test.c
% ./a.out
zsh: abort (core dumped)  ./a.out
% clang-7.0 -v
clang version 7.0.0 (trunk 323624)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/hiroki-maeda/opt/clang-7.0/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9.3
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.4.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.0.0
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.4.0
Candidate multilib: .;@m64
Selected multilib: .;@m64

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