nickdesaulniers added inline comments.
================ Comment at: llvm/lib/Target/X86/X86ISelLowering.cpp:96 +static cl::opt<bool> SkipRaxSetup( + "x86-skip-rax-setup", cl::init(false), ---------------- MaskRay wrote: > nickdesaulniers wrote: > > If it's a command line option rather than encoded in the IR, then this > > won't be handled correctly under LTO (we support building the x86 linux > > kernel under LTO), unless the linker re-passes the flag. I've been trying > > to avoid that by encoding this information properly in IR rather than rely > > on codegen command line options which I find brittle. Please see > > https://reviews.llvm.org/D103928 as an example. > This depends on how frequent the feature is used. > > I see that `arch/x86/Makefile` may add `-mskip-rax-setup` which is presumably > used by all C files, so a module flag metadata suffices. If there are > mix-and-match cases for different modules (e.g. ssp/nossp) a function > attribute may be used. If a feature is really obscure than I might not > consider wasting an IR attribute on it. Arguably if a feature is sufficient > obscure we may not want to port it from GCC at all. > > So "This fixes pr23258." in the description should state the use case to give > archaeologists a hint why the feature is added. That's fine, though then we should add a test for new module level IR using llvm-link, IMO, since this (and many `-m` flags) imply an ABI breakage across modules with mismatched use of this flag. > Arguably if a feature is sufficient obscure we may not want to port it from > GCC at all. In this case, I think@hjl.tools has some nice numbers to justify this feature in [[ https://patchwork.ozlabs.org/project/gcc/patch/20141218131150.ga32...@intel.com/ | their patch ]]. I can run similar numbers on clang built kernels, but it seems nice to have. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D112413/new/ https://reviews.llvm.org/D112413 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
