smithp35 wrote: I can chime in with an opinion but unfortunately I think it may be different to everyone elses!
This is a bit of an awkward situation as I think we have to balance several things: * Consistency between v8-R and AArch32 (ARM) and AArch64 (more consistent the better) * Consistency between clang and gcc (more consistent the better) * Historical behaviour of -march=armv8-r (how often is it used vs -mcpu) * Historical behaviour of -mcpu=cortex-r82 (keeping these stable as this is the most specific target) * Consistency with other -march and -mcpu with respect to feature enablement heuristics (helps transition between options). As a general rule/heuristic for Arm feature enablement going forward, you will find exceptions to these rules in LLVM, particularly pre Armv8. we tend towards: * -march enables the mandatory features, but not the optional features, with specific exceptions such as SVE for Armv9 and floating point and SIMD for AArch64 Armv8 * -mcpu enables the mandatory and optional features, with specific exceptions such as crypto The Cortex-R series are intended for deeply embedded applications so it is normally possible for a user to directly target the CPU rather than the architecture. As there is only one v8-R CPU I'm fully expecting most users to use `-mcpu=cortex-r82` rather than `-march=armv8-r`. With these in mind. I propose: * `-march=armv8-r` enables the mandatory architectural features and including the mandatory minimum FPU given that all implementations of v8-R have that. It doesn't make sense to make it optional for puritys sake. * Make `-march=armv8-r` use a generic CPU so that we don't need to change cortex-r82. Yes this will make the performance of v8-R worse without `-mtune`, but I think it is preferable to keep -mcpu=cortex-r82 unaltered as that is what most people will be using. * Do not change -mcpu=cortex-r82 from its current default. This is again an opinion based the weights that I put on the trade-off dimensions. https://github.com/llvm/llvm-project/pull/88287 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
