================ @@ -30,6 +30,15 @@ set(LLVM_LINK_COMPONENTS TransformUtils ) +# Workaround for MSVC ARM64 performance regression: disable all optimizations (/Od) +# and then enable back all /O2 options except one. +if(NOT CMAKE_BUILD_TYPE MATCHES Debug + AND MSVC + AND MSVC_VERSION VERSION_GREATER_EQUAL 1932 + AND CMAKE_SYSTEM_PROCESSOR MATCHES "ARM64") + set_source_files_properties(CGBuiltin.cpp PROPERTIES COMPILE_FLAGS "/Od /Gw /Oi /Oy /Gy /Ob2 /Ot /GF") ---------------- lxbndr wrote:
Thanks for the review! I think I have to elaborate a little (and I apologize for not making this clear enough in the PR description). We're not going to just throw a bunch of optimization flags, of course. The flag I actually intend to alter is `/O2`. According to the [reference](https://learn.microsoft.com/en-us/cpp/build/reference/o1-o2-minimize-size-maximize-speed?view=msvc-170), `/O2` is the equivalent of `/Og /Oi /Ot /Oy /Ob2 /GF /Gy` (I even see this in the compiler frontend invocation). I want to suppress the `/Og` and leave others in effect. This is done by adding `/Od` first (which cancels all `/O2` flags), and then adding "O2-minus-Og" flags back. Probably, the `/Gw` flag is the only unnecessary flag here, as it is not part of the `/O...` set (and it is not affected by `/Od` either). It is also worth to mention that `set_source_files_properties` does not override flag set. It appends specified flags to other configured flags. That's why I had to use `/Od` to cancel already existing `/O2`. I fully understand the intention to not break existing configuration. And I think I see how this can be improved. Instead of assuming all non-debug builds have optimizations enabled, we should seek for `/O2`/`/O1` flags directly, and adjust resulting flag set according to each case. @tru WDYT? Does this sound better? https://github.com/llvm/llvm-project/pull/65215 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
