Yunzezhu added a comment. In D151867#4400255 <https://reviews.llvm.org/D151867#4400255>, @craig.topper wrote:
> From the C language perspective with this change, __builtin_clz/ctz is still > considered undefined for 0 and code that uses it is ill-formed. > `isCLZForZeroUndef` is only intended to prevent the middle end from > optimizing based on the undefinedness and creating surprises. See also > https://discourse.llvm.org/t/should-ubsan-detect-0-input-to-builtin-clz-ctz-regardless-of-target/71060 I see __builtin_clz/ctz returning an undefined value for 0 input matches gcc's document, but when I test __builtin_clz/ctz with 0 input on gcc, it returns a valid value rather than an undefined value. It looks gcc does not follow gcc's document. I'm not sure which one is better that match document to return undefined for 0, or match gcc's behavior to return defined value? Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D151867/new/ https://reviews.llvm.org/D151867 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
