how to generate both IR and object file

Clang Frontend
1

Hi,

I use the -emit-llvm flag to generate IR files and use LTO to link them together to produce the final executable. Sometimes LTO gives me link-time errors, so I want to avoid using it, yet I need IR files.

Question: Is there a way to instruct clang to generate *both* an IR file and a regular object file at compile-time, and during the link time, use the object files only, while leaving out the IR files?

Thanks,
JS

2

Surely you can just change the way the Makefile behaves to do what you want.
At the moment you have:
compile dependencies:
.c/.cpp -> .bc (clang)
link dependencies for LTO:
Many .bc -> big .so or .a or exe

Change this to:
compile dependencies
.c/.cpp -> .bc (with clang)
.bc -> .o (with llc)
link dependencies:
many .o -> big .so or .a or exe

A normal compiler would do this:
compile dependencies
.c/.cpp -> .o (with clang)
link dependencies:
many .o -> big .so or .a or exe

So, you are breaking the compile dependencies into two.

3

Hi,

I use the -emit-llvm flag to generate IR files and use LTO to link them together to produce the final executable. Sometimes LTO gives me link-time errors, so I want to avoid using it, yet I need IR files.

Question: Is there a way to instruct clang to generate *both* an IR file and a regular object file at compile-time, and during the link time, use the object files only, while leaving out the IR files?

That isn't supported by the standard driver and frontend but it's a perfectly reasonable feature to request.

It's missing mostly for historical reasons -- the frontend action pipeline wasn't designed to be composable, meaning you can only do one thing per invocation.

The limitation doesn't apply if you use the clang C++ API to build a custom tool.

Alp.

4

Thanks guys. Yes, it would be awesome to have this feature in the future
release.

Modifying the build environment as James suggested isn¹t an option for me
for political reasons with other teams I¹m working with.

5

This reminds me of another recent question where someone wanted to run both compile and analyze actions. Is there anything that actually prevents us from running multiple actions?