[llvm] r349068 - Don't add unnecessary compiler flags to llvm-config output

[Finkel, Hal J. via llvm-commits]

Hi, Tom,

Are -fno-exceptions -fno-rtti also necessary? My students this quarter
complained about this quite a bit ;)

 -Hal

On 12/13/18 12:21 PM, Tom Stellard via llvm-commits wrote:
> Author: tstellar
> Date: Thu Dec 13 10:21:23 2018
> New Revision: 349068
>
> URL: http://llvm.org/viewvc/llvm-project?rev=349068&view=rev
> Log:
> Don't add unnecessary compiler flags to llvm-config output
>
> Summary:
> llvm-config --cxxflags --cflags, should only output the minimal flags
> required to link against the llvm libraries.  They currently contain
> all flags used to compile llvm including flags like -g, -pedantic,
> -Wall, etc, which users may not always want.
>
> This changes the llvm-config output to only include flags that have been
> explictly added to the COMPILE_FLAGS property of the llvm-config target
> by the llvm build system.
>
> llvm.org/PR8220
>
> Output from llvm-config when running cmake with:
> cmake -G Ninja .. -DCMAKE_CXX_FLAGS=-funroll-loops
>
> Before:
>
> --cppflags: -I$HEADERS_DIR/llvm/include -I$HEADERS_DIR/llvm/build/include
>             -D_GNU_SOURCE -D_DEBUG -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS
> --cflags:   -I$HEADERS_DIR/llvm/include -I$HEADERS_DIR/llvm/build/include
>             -fPIC -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings \
>             -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough \
>             -Wno-comment -fdiagnostics-color -g -D_GNU_SOURCE -D_DEBUG -D__STDC_CONSTANT_MACROS \
>             -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS
> --cxxflags: -I$HEADERS_DIR/llvm/include -I$HEADERS_DIR/llvm/build/include\
>             -funroll-loops -fPIC -fvisibility-inlines-hidden -Werror=date-time -std=c++11 -Wall \
>             -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers \
>             -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-maybe-uninitialized \
>             -Wno-class-memaccess -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wno-comment \
>             -fdiagnostics-color -g  -fno-exceptions -fno-rtti -D_GNU_SOURCE -D_DEBUG \
>             -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS"
>
> After:
>
> --cppflags: -I$HEADERS_DIR/llvm/include -I$HEADERS_DIR/llvm/build/include \
>             -D_GNU_SOURCE -D_DEBUG -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS
> --cflags:   -I$HEADERS_DIR/llvm/include -I$HEADERS_DIR/llvm/build/include \
>             -D_GNU_SOURCE -D_DEBUG -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS
> --cxxflags: -I$HEADERS_DIR/llvm/include -I$HEADERS_DIR/llvm/build/include \
>              -std=c++11   -fno-exceptions -fno-rtti \
>              -D_GNU_SOURCE -D_DEBUG -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS
>
> Reviewers: sylvestre.ledru, infinity0, mgorny
>
> Reviewed By: sylvestre.ledru, mgorny
>
> Subscribers: mgorny, dmgreen, llvm-commits
>
> Differential Revision: https://reviews.llvm.org/D55391
>
> Modified:
>     llvm/trunk/tools/llvm-config/CMakeLists.txt
>
> Modified: llvm/trunk/tools/llvm-config/CMakeLists.txt
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/llvm-config/CMakeLists.txt?rev=349068&r1=349067&r2=349068&view=diff
> ==============================================================================
> --- llvm/trunk/tools/llvm-config/CMakeLists.txt (original)
> +++ llvm/trunk/tools/llvm-config/CMakeLists.txt Thu Dec 13 10:21:23 2018
> @@ -29,12 +29,20 @@ string(REPLACE ";" " " SYSTEM_LIBS "${SY
>  # Fetch target specific compile options, e.g. RTTI option
>  get_property(COMPILE_FLAGS TARGET llvm-config PROPERTY COMPILE_FLAGS)
>  
> +# The language standard potentially affects the ABI/API of LLVM, so we want
> +# to make sure it is reported by llvm-config.
> +# NOTE: We don't want to start extracting any random C/CXX flags that the
> +# user may add that could affect the ABI.  We only want to extract flags
> +# that have been added by the LLVM build system.
> +string(REGEX MATCH "-std=[^ ]\+" LLVM_CXX_STD_FLAG ${CMAKE_CXX_FLAGS})
> +string(REGEX MATCH "-std=[^ ]\+" LLVM_C_STD_FLAG ${CMAKE_C_FLAGS})
> +
>  # Use configure_file to create BuildVariables.inc.
>  set(LLVM_SRC_ROOT ${LLVM_MAIN_SRC_DIR})
>  set(LLVM_OBJ_ROOT ${LLVM_BINARY_DIR})
> -set(LLVM_CPPFLAGS "${CMAKE_CPP_FLAGS} ${CMAKE_CPP_FLAGS_${uppercase_CMAKE_BUILD_TYPE}} ${LLVM_DEFINITIONS}")
> -set(LLVM_CFLAGS "${CMAKE_C_FLAGS} ${CMAKE_C_FLAGS_${uppercase_CMAKE_BUILD_TYPE}} ${LLVM_DEFINITIONS}")
> -set(LLVM_CXXFLAGS "${CMAKE_CXX_FLAGS} ${CMAKE_CXX_FLAGS_${uppercase_CMAKE_BUILD_TYPE}} ${COMPILE_FLAGS} ${LLVM_DEFINITIONS}")
> +set(LLVM_CPPFLAGS "${LLVM_DEFINITIONS}")
> +set(LLVM_CFLAGS "${LLVM_C_STD_FLAG} ${LLVM_DEFINITIONS}")
> +set(LLVM_CXXFLAGS "${LLVM_CXX_STD_FLAG} ${COMPILE_FLAGS} ${LLVM_DEFINITIONS}")
>  set(LLVM_BUILD_SYSTEM cmake)
>  set(LLVM_HAS_RTTI ${LLVM_CONFIG_HAS_RTTI})
>  set(LLVM_DYLIB_VERSION "${LLVM_VERSION_MAJOR}${LLVM_VERSION_SUFFIX}")
>
>
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-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory