How to compile some modules in LLVM with debug mode, others with release mode?

Question

Full debug compilation requires too much memory. My machine is only 4GB of memory. I would like to debug a module using debug compiler, other modules with release compiling.

In general, I build LLVM in debug mode or release mode using the following commands:

cmake /home/llvm380 -DCMAKE_BUILD_TYPE="Release" 

cmake /home/llvm380 -DCMAKE_BUILD_TYPE="Debug"

The choice of a build type has impact on a whole build process. Full debug build is not convenient to debug as it needs about 13GB memory. I only want to debug a small part of a code.

Example: I want to make llvm/lib/IR module debug build. How to modify the CMakeLists.txt in llvm\lib\IR?

It is probably not possible without hacking on LLVM's CMakeLists files. But it is definitely possible if you are ready to hack on them. — Stanislav Pankevich, Mar 19 '17 at 12:16
I don't understand why this question is on hold. Seems like the voters are completely out of the context, since the question is absolutely clear and valid. — AlexDenisov, Mar 19 '17 at 19:16
@freyone, your question is very clear to me but I can see how it can confuse the folks who voted for this question to be closed as "too broad". Please fill in a bit more details like that you are building LLVM from source and want to debug its specific module etc. — Stanislav Pankevich, Mar 19 '17 at 19:17

score 2 · Answer 1 · edited May 23 '17 at 12:00

LLVM works with CMake, so to enable debug mode on specific modules you either need to enable -g flag on particular files or enable it on the whole build targets. Most likely you will need:

COMPILE_FLAGS or COMPILE_DEFITIONS target property (see Difference between COMPILE_FLAGS and COMPILE_OPTIONS) or COMPILE_FLAGS source file property.

I have tried this quickly on one project, on both file- and target-levels and can confirm that it is doable.

Let's assume you have one file MySourceFile.cpp and a build target MyTarget. Below I am adding -hack-target and -hack-file to better see where this results in.

set(my_source_files
  MySourceFile.cpp
)

add_library(MyTarget SHARED ${my_source_files} ...)

Adding -g flag on a target level:

get_target_property(my_target_compile_flags MyTarget COMPILE_FLAGS)
if (NOT my_target_compile_flags)
  set(my_target_compile_flags "")
endif()
set_target_properties(MyTarget
                      PROPERTIES COMPILE_OPTIONS  
                      "${my_target_compile_options} -g -hack-target")

Adding -g flag on a source file level:

get_source_file_property(my_source_file_compile_flags
                         MySource.cpp
                         COMPILE_FLAGS)

if (NOT my_source_file_compile_flags)
  set(my_source_file_compile_flags "")
endif()
set_source_files_properties(MySource.cpp
                            PROPERTIES
                            COMPILE_FLAGS
                            "${my_source_file_compile_flags} -g -hack-file")

From the above lines the CMake helper functions can be made for your convenience of enabling -g flag on the stuff you need easier.

I can speak of how this works on Ninja and Xcode:

Ninja

$ grep -ri "hack-" BuildNinja

BuildNinja//build.ninja:  FLAGS = -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk -fPIC    -g -hack-target -std=c++11  -g -hack-file

Xcode

In Xcode -g of a target level goes to "Generate Debug Symbols" property:

This is how flags look like:

Target one:

File one:

according you suggestion.i modified Cmakelists.txt in my modules. after then,how to cmake? still "cmake /home/llvm380 -DCMAKE_BUILD_TYPE="Release" " need to add "-g"? — freyone, Mar 22 '17 at 06:32
No, you only add `-g` in the CMakeLists as I showed. No need to pass it anywhere else. — Stanislav Pankevich, Mar 22 '17 at 06:38
And yes, you have to run your `cmake ...` command again. Feel free to use CMake's `message` command to debug your CMakeLists files. Example: `message(STATUS "This is debug string you will see when you run cmake")`. See also http://stackoverflow.com/a/5403778/598057. — Stanislav Pankevich, Mar 22 '17 at 07:20
Did you mean to get_target_property of COMPILE_OPTIONS instead of COMPILE_FLAGS? — Peter Tseng, Oct 09 '17 at 23:03
I think I posted the working code at the time of my answer. You probably know that they are the same thing: https://stackoverflow.com/questions/24302073/difference-between-compile-flags-and-compile-options, right. — Stanislav Pankevich, Oct 10 '17 at 07:57

How to compile some modules in LLVM with debug mode, others with release mode?

1 Answers1