[PATCH] D95032: [AArch64][GlobalISel] Make G_USUBO legal and select it

[Mitch Phillips via Phabricator via llvm-commits]

hctim added a comment.

Hi, looks like this patch broke UBSan on aarch64:

Looks like it flips the condition on unsigned-integer-overflow:

  volatile uint32_t a = 1;
  volatile uint32_t b = 2;
  volatile uint32_t c = a - b;



      17bc:	52800028 	mov	w8, #0x1
      17c0:	71000908 	subs	w8, w8, #0x2
  prev:
      17c4:	54000142 	b.cs	17ec no_problems  // b.hs, b.nlast
      // fallthrough to __ubsan_handle_sub_overflow
  now:
      17c4:	1a9f37e8 	cset	w8, cs  // cs = hs, nlast
      17c8:	360000c8 	tbz	w8, #0, no_problems
      // fallthrough to __ubsan_handle_sub_overflow

The reverse is also true, perfectly valid operands now fail:

  int main() {
    volatile uint32_t a = 3;
    volatile uint32_t b = 2;
    volatile uint32_t c = a - b;
  }

  $ clang a.cpp -fsanitize=unsigned-integer-overflow
  $ ./a.out
  runtime error: unsigned integer overflow: 3 - 2 cannot be represented in type 'unsigned int'
  SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior

This was caught on our sanitizer Android buildbots: http://lab.llvm.org:8011/#/builders/77/builds/3082


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D95032/new/

https://reviews.llvm.org/D95032