[PATCH] D149423: [ValueTracking] Use knownbits interface for determining if `div`/`rem` are safe to speculate

[Alexander Kornienko via Phabricator via llvm-commits]

alexfh added a comment.

This patch is causing a miscompile:

  $ cat q.cc 
  extern unsigned q();
  int main() {
    unsigned qq = q();
    if (qq == 0) qq = 1;
    int rows = 8192 / qq;
    if (rows == 0) rows = 1;
    return rows;
  }
  $ cat w.cc
  unsigned q() { return 524288; }
  $ clang -fsanitize=memory -O2 q.cc w.cc && ./a.out
  MemorySanitizer:DEADLYSIGNAL
  ==885020==ERROR: MemorySanitizer: FPE on unknown address 0x0000002cc0c4 (pc 0x0000002cc0c4 bp 0x000000000001 sp 0x7ffd25df6e50 T885020)
  ...

Please revert or fix soon. Thanks!


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D149423/new/

https://reviews.llvm.org/D149423