khchen planned changes to this revision. khchen marked an inline comment as done. khchen added a comment.
The problem is how `-mcpu` interact with explicitly specified `-march` (or target features). 1. in GCC, -mcpu is only used to chose the pipeline model, 2. I also read this <https://community.arm.com/developer/tools-software/tools/b/tools-software-ides-blog/posts/compiler-flags-across-architectures-march-mtune-and-mcpu> article talking about the X86 and ARM to handle those options. -march=X: Tells the compiler that X is the minimal architecture the binary must run on. The compiler is free to use architecture-specific instructions. This flag behaves differently on Arm and x86. On Arm, -march does not override -mtune, but on x86 -march will override both -mtune and -mcpu. -mtune=X: Tells the compiler to optimize for microarchitecture X but does not allow the compiler to change the ABI or make assumptions about available instructions. This flag has the more-or-less the same meaning on Arm and x86. -mcpu=X: On Arm, this flag is a combination of -march and -mtune. It simultaneously specifies the target architecture and optimizes for a given microarchitecture. On x86 this flag is a deprecated synonym for -mtune. So maybe it makes sense to treat those flags behaves differently on different target . 3. I also tried llc to specific -mcpu and -attr (similar to -march, target-feature) in ARM, -attr will over write the default target-feature in -mcpu. on RISC-V, in sometime (or most?) we have same pipeline model but support different extension combination, so I think maybe distinguishing the purpose of -mcpu and -march and make them with no interaction is a good idea. (behavior is equal to GCC) Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D71124/new/ https://reviews.llvm.org/D71124 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
