From 701f3faf6e70374ba8f372f38d1039f13e8ef7cd Mon Sep 17 00:00:00 2001
From: Tom Stellard <tstellar@redhat.com>
Date: Thu, 13 Dec 2018 18:21:23 +0000
Subject: [PATCH] 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

llvm-svn: 349068
---
 llvm/tools/llvm-config/CMakeLists.txt | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/tools/llvm-config/CMakeLists.txt b/tools/llvm-config/CMakeLists.txt
index a0bd36c..a7db173 100644
--- a/tools/llvm-config/CMakeLists.txt
+++ b/tools/llvm-config/CMakeLists.txt
@@ -29,12 +29,20 @@ string(REPLACE ";" " " SYSTEM_LIBS "${SYSTEM_LIBS}")
 # 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}")
-- 
1.8.3.1