How to make clang compile to llvm IR

Question

I want clang to compile my C C   code to LLVM bytecode rather than binary executable  How can I achieve that  And if I get the LLVM bytecode  how can I take it to further compile it to binary executable    Basically I want to add some of my own code to the LLVM bytecode before compiling to binary executable

User · Answer

If you have multiple source files  you probably actually want to use link-time-optimization to output one bitcode file for the entire program   The other answers given will cause you to end up with a bitcode file for every source file   Instead  you want to compile with link-time-optimization  clang -flto -c program1 c -o program1 o clang -flto -c program2 c -o program2 o   and for the final linking step  add the argument -Wl -plugin-opt also-emit-llvm  clang -flto -Wl -plugin-opt also-emit-llvm program1 o program2 o -o program   This gives you both a compiled program and the bitcode corresponding to it  program bc    You can then modify program bc in any way you like  and recompile the modified program at any time by doing  clang program bc -o program   although be aware that you need to include any necessary linker flags  for external libraries  etc  at this step again   Note that you need to be using the gold linker for this to work   If you want to force clang to use a specific linker  create a symlink to that linker named  ld  in a special directory called  fakebin  somewhere on your computer  and add the option   -B home jeremy fakebin   to any linking steps above

User · Answer

Did you read clang documentation   You re probably looking for -emit-llvm

User · Answer

Use  clang -emit-llvm -o foo bc -c foo c clang -o foo foo bc

User · Answer

Given some C C   file foo c    gt  clang -S -emit-llvm foo c   Produces foo ll which is an LLVM IR file   The -emit-llvm option can also be passed to the compiler front-end directly  and not the driver by means of -cc1    gt  clang -cc1 foo c -emit-llvm   Produces foo ll with the IR  -cc1 adds some cool options like -ast-print  Check out -cc1 --help for more details     To compile LLVM IR further to assembly  use the llc tool    gt  llc foo ll   Produces foo s with assembly  defaulting to the machine architecture you run it on   llc is one of the LLVM tools - here is its documentation

User · Answer

If you have multiple files and you don t want to have to type each file  I would recommend that you follow these simple steps  I am using clang-3 8 but you can use any other version     generate all  ll files  clang-3 8 -S -emit-llvm   c  link them into a single one  llvm-link-3 8 -S -v -o single ll   ll   Optional  Optimise your code  maybe some alias analysis   opt-3 8 -S -O3 -aa -basicaaa -tbaa -licm single ll -o optimised ll  Generate assembly  generates a optimised s file   llc-3 8 optimised ll  Create executable  named a out   clang-3 8 optimised s

[c] How to make clang compile to llvm IR

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