chaitanyav wrote: > > > > Typically we don't bother to implement these unless libc starts using > > > > these, or needs them. Making builtins for these functions without the > > > > library needs them is kinda silly. > > > > DO we have a request for these coming from the libc maintainers? > > > > > > > > > I think they're important for two reasons: 1) we're going to want > > > constexpr support for these for the same reason we want constexpr support > > > for `strlen` in C so defining them as recognized library builtins is the > > > way we do that, and 2) I think libc is going to want to have full support > > > for bit-precise integer types and that's easier to support from a builtin > > > currently. That said, CC @michaelrj-google for additional opinions > > > > > > From the libc side having these builtins would be handy for both of the > > reasons Aaron mentioned. For optimization it would be helpful if the > > compiler could replace the libcall with a builtin, since things like > > `leading_zeros` can sometimes be reduced to a single instruction. Actually > > calling these bit functions as functions is unlikely to be optimal. CC: > > @enh-google > > We also should run this through our test suites to see if there is any > discrepancy, or missing tests for edge cases.
@enh-google I have added those tests to the patch. Also, have verified the outputs with gcc. ``` ╰─ gcc -v Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/15.2.1/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: /build/gcc/src/gcc/configure --enable-languages=ada,c,c++,d,fortran,go,lto,m2,objc,obj-c++,rust,cobol --enable-bootstrap --prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=https://gitlab.archlinux.org/archlinux/packaging/packages/gcc/-/issues --with-build-config=bootstrap-lto --with-linker-hash-style=gnu --with-system-zlib --enable-__cxa_atexit --enable-cet=auto --enable-checking=release --enable-clocale=gnu --enable-default-pie --enable-default-ssp --enable-gnu-indirect-function --enable-gnu-unique-object --enable-libstdcxx-backtrace --enable-link-serialization=1 --enable-linker-build-id --enable-lto --enable-multilib --enable-plugin --enable-shared --enable-threads=posix --disable-libssp --disable-libstdcxx-pch --disable-werror Thread model: posix Supported LTO compression algorithms: zlib zstd gcc version 15.2.1 20260209 (GCC) ``` [stdbit_result.txt](https://github.com/user-attachments/files/26636938/stdbit_result.txt) https://github.com/llvm/llvm-project/pull/185978 _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
