llvm-project

c719d7b3 - [FMV][AArch64] Do not optimize away runtime checks for implied features (#99522)

[FMV][AArch64] Do not optimize away runtime checks for implied features (#99522) When generating the body of the ifunc resolver, clang skips runtime checks for features that are implied from the command line. We bend this rule for certain features (memtag, bti, dgh), but this happens quite arbitrarily in my opinion. The reasoning is that some features are in the HINT instruction space, meaning they operate as NOPs if the hardware does not support them. Still the user wants to detect their presence with runtime checks. See #90928 for details. I think we should always perform runtime checks regardless of the feature and then try to statically resolve calls whenever a function is compiled with a sufficiently high set of architecture features (so including target/target_version/target_clones attributes, and command line options). This is what GCC does. We have an open PR in LLVM GlobalOpt since it was suggested not to perform such codegen optimizations in clang anyway. See #87939.