[GitHub] [arrow] mapleFU commented on a diff in pull request #15022: ARROW-18231: [C++][CMake] Add support for overriding optimization level

["mapleFU (via GitHub)" <gi...@apache.org>]

mapleFU commented on code in PR #15022:
URL: https://github.com/apache/arrow/pull/15022#discussion_r1104001248


##########
cpp/cmake_modules/SetupCxxFlags.cmake:
##########
@@ -604,76 +604,42 @@ endif()
 # For all builds:
 # For CMAKE_BUILD_TYPE=Debug
 #   -ggdb: Enable gdb debugging
-# For CMAKE_BUILD_TYPE=FastDebug
-#   Same as Debug, except with some optimizations on.
 # For CMAKE_BUILD_TYPE=Release
-#   -O2: Enable all compiler optimizations
+#   -O2 (not -O3): Enable compiler optimizations
 #   Debug symbols are stripped for reduced binary size.
 # For CMAKE_BUILD_TYPE=RelWithDebInfo
 #   Same as Release, except with debug symbols enabled.
 
 if(NOT MSVC)
-  string(REPLACE "-O3" "" CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE}")
-  string(REPLACE "-O3" "" CMAKE_CXX_FLAGS_RELWITHDEBINFO
-                 "${CMAKE_CXX_FLAGS_RELWITHDEBINFO}")
-
-  set(RELEASE_FLAGS "-O2 -DNDEBUG")
+  set(C_RELEASE_FLAGS "")
+  if(CMAKE_C_FLAGS_RELEASE MATCHES "-O3")
+    string(APPEND C_RELEASE_FLAGS " -O2")

Review Comment:
   Hi, kou, does this patch means, when we use release, the default build is "-O3 -DNDEBUG -O2", would it use O2 to final build it rather than O3? @kou 



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