GCC flags to get LTO bitcode

Question

I have been using LLVM/Clang and its Intermediate Representation(IR) for a while now. I have recently started working with GCC. I want to dump IR bitcode to a file, similar to (-flto -save-temps flag) in LLVM.

I can get gimple IR using '-fdump-tree-cfg-raw' flag while building, but with multiple input files, this generates an a '.gimple' file for each source.

To get the view of the entire program, in LLVM, I used '-flto -Wl,-plugin-opt=save-temps' in LDFLAGS. What is the correct way of getting the same behavior in GCC.

I tried using 'gcc -fdump-tree-cfg-raw -flto -save-temps src1.c main.c', but I do not get the combined IR file. The outputs include .o,.s,.i files for each source and .cfg file for each.

Answer 1

You don't see the merged file because this pass was not executed by lto. All the passes executed by cc1 are not necessarily executed by lto. A solution could be to use fdump-tree-all option

gcc -flto -fdump-tree-all -o exec x.c y.c

you will get all the gimple files for the entire program. For each pass executed you will get exec.ltrans.xxxt.pass_name . Otherwise, if you don't want to use fdump-tree-all you must be sure that the pass you want to dump will be executed by the lto.