[clang] Workaround for MSVC ARM64 build performance regression (PR #65215)

[Tobias Hieta via cfe-commits]

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@@ -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")
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tru wrote:

You are setting these settings for all configurations and erasing the other flags set for these files. I don't think that's the right solution. I would rather you grab the current compile_flags and then substitute the optimization flags only.

https://github.com/llvm/llvm-project/pull/65215