Yunzezhu abandoned this revision. Yunzezhu added a comment. In D151867#4401987 <https://reviews.llvm.org/D151867#4401987>, @craig.topper wrote:
> In D151867#4401952 <https://reviews.llvm.org/D151867#4401952>, @Yunzezhu > wrote: > >> 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? > > From what I can see in the assembly here https://godbolt.org/z/s4qqz83EK, > gcc's undefined behavior sanitizer does consider an input of 0 to be > undefined. Got it. 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
