[PATCH] D107420: [sema] Disallow __builtin_mul_overflow under special condition.

Thu Aug 5 10:33:44 PDT 2021

craig.topper added a comment.

In D107420#2929039 <https://reviews.llvm.org/D107420#2929039>, @aaron.ballman wrote:

> In D107420#2928975 <https://reviews.llvm.org/D107420#2928975>, @craig.topper wrote:
>
>> I put up a patch for a simple fix for this in the backend. https://reviews.llvm.org/D107581  The generated code is not optimal, but maybe better than frontend workarounds.
>
> Thanks for putting up the backend fix! That's much better than frontend workarounds.

Looks like I may have opened a small can of worms. In 32-bit mode, a __builtin_mul_overflow of _ExtInt(128) producing a signed result generates a call to _muloti4 which neither compiler-rt or libgcc implement in 32-bit mode. In 64-bit mode only compiler-rt implements _muloti4 for x86-64.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D107420/new/

https://reviews.llvm.org/D107420