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

[Alexander Smarus via cfe-commits]

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

>From c97d9a28ef8cdb232670a960a46bc30b269983f7 Mon Sep 17 00:00:00 2001
From: Alexander Smarus <bender at readdle.com>
Date: Tue, 19 Sep 2023 00:34:54 +0300
Subject: [PATCH] Workaround for MSVC ARM64 build performance regression

---
 clang/lib/CodeGen/CMakeLists.txt              | 20 +++++++++++++++++++
 .../Tooling/Inclusions/Stdlib/CMakeLists.txt  | 20 +++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/clang/lib/CodeGen/CMakeLists.txt b/clang/lib/CodeGen/CMakeLists.txt
index 1debeb6d9cce9e0..2dd93a57f4e22d2 100644
--- a/clang/lib/CodeGen/CMakeLists.txt
+++ b/clang/lib/CodeGen/CMakeLists.txt
@@ -30,6 +30,26 @@ set(LLVM_LINK_COMPONENTS
   TransformUtils
   )
 
+# Workaround for MSVC ARM64 performance regression:
+# https://developercommunity.visualstudio.com/t/Compiling-a-specific-code-for-ARM64-with/10444970
+# Since /O1 and /O2 represent a set of optimizations,
+# our goal is to disable the /Og flag while retaining the other optimizations from the /O1|/O2 set
+if(MSVC AND NOT CMAKE_CXX_COMPILER_ID MATCHES Clang
+    AND MSVC_VERSION VERSION_GREATER_EQUAL 1932
+    AND CMAKE_SYSTEM_PROCESSOR MATCHES "ARM64")
+
+  string(TOUPPER "${CMAKE_BUILD_TYPE}" uppercase_CMAKE_BUILD_TYPE)
+  string(REGEX MATCHALL "/[Oo][12]" opt_flags "${CMAKE_CXX_FLAGS} ${CMAKE_CXX_FLAGS_${uppercase_CMAKE_BUILD_TYPE}}")
+  if (opt_flags)
+    if(opt_flags MATCHES "1$")
+      set(opt_flags "/Od;/Os;/Oy;/Ob2;/GF;/Gy")
+    elseif (opt_flags MATCHES "2$")
+      set(opt_flags "/Od;/Oi;/Ot;/Oy;/Ob2;/GF;/Gy")
+    endif()
+    set_source_files_properties(CGBuiltin.cpp PROPERTIES COMPILE_OPTIONS "${opt_flags}")
+  endif()
+endif()
+
 add_clang_library(clangCodeGen
   ABIInfo.cpp
   ABIInfoImpl.cpp
diff --git a/clang/lib/Tooling/Inclusions/Stdlib/CMakeLists.txt b/clang/lib/Tooling/Inclusions/Stdlib/CMakeLists.txt
index 0f52c3590ac9af1..ed323ab3528b104 100644
--- a/clang/lib/Tooling/Inclusions/Stdlib/CMakeLists.txt
+++ b/clang/lib/Tooling/Inclusions/Stdlib/CMakeLists.txt
@@ -1,3 +1,23 @@
+# Workaround for MSVC ARM64 performance regression:
+# https://developercommunity.visualstudio.com/t/Compiling-a-specific-code-for-ARM64-with/10444970
+# Since /O1 and /O2 represent a set of optimizations,
+# our goal is to disable the /Og flag while retaining the other optimizations from the /O1|/O2 set
+if(MSVC AND NOT CMAKE_CXX_COMPILER_ID MATCHES Clang
+    AND MSVC_VERSION VERSION_GREATER_EQUAL 1932
+    AND CMAKE_SYSTEM_PROCESSOR MATCHES "ARM64")
+
+  string(TOUPPER "${CMAKE_BUILD_TYPE}" uppercase_CMAKE_BUILD_TYPE)
+  string(REGEX MATCHALL "/[Oo][12]" opt_flags "${CMAKE_CXX_FLAGS} ${CMAKE_CXX_FLAGS_${uppercase_CMAKE_BUILD_TYPE}}")
+  if (opt_flags)
+    if(opt_flags MATCHES "1$")
+      set(opt_flags "/Od;/Os;/Oy;/Ob2;/GF;/Gy")
+    elseif (opt_flags MATCHES "2$")
+      set(opt_flags "/Od;/Oi;/Ot;/Oy;/Ob2;/GF;/Gy")
+    endif()
+    set_source_files_properties(StandardLibrary.cpp PROPERTIES COMPILE_OPTIONS "${opt_flags}")
+  endif()
+endif()
+
 add_clang_library(clangToolingInclusionsStdlib
   StandardLibrary.cpp