Dumping compiled module as LLVM IR bitcode after certain optimization passes

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#1

Hello.
     Is there a possibility to instruct at command line the clang or the opt tools to emit LLVM bitcode file after a certain optimization pass such as LoopVectorize (or all optimization passes)? (This question was asked also at compiler construction - Dump IR after each llvm optimization (each pass), both llvm ir passes and backend debugging - Stack Overflow .)
     As far as I can see giving:
       clang -save-temps ...
     generates a .bc file for the compiled module just before passing the module to the optimization passes (opt).

     An alternative I have is to programmatically generate the corresponding bitcode file at the right time after finishing the pass in discussion - see, for example, llvm - writing module to .bc bitcode file - Stack Overflow, methods WriteBitcodeToFile() or WriteModule() .

   Thank you,
     Alex

#2

Hi,

Usually we disable the llvm optimizations (clang -mllvm disable-llvm-optzns ) and then use opt to run the passes till the point of interest. I don’t know of a shortcut in clang (the new PassManager will make it possible to pass an arbitrary pipeline with a string, but not there yet).

#3

Also, if I have a small test-case, using `clang -mllvm -print-after-all` is convenient to get the IR at any point.
Adding "-filter-print-funcs” can help reducing the amount in the output to a single function (or a list of functions), for example:
`clang -mllvm -filter-print-funcs=_Z3foov -mllvm -print-after-all`.

(There is a print-after option but it does not work in clang).