[PATCH] D107420: [sema] Disallow __builtin_mul_overflow under special condition.
Craig Topper via Phabricator via cfe-commits
cfe-commits at lists.llvm.org
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
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