Equivalent of -ftree-vectorizer-verbose for clang

Question

The question is about how to make clang print information on which loops (or other parts of code) have been vectorized. GCC has a command line switch named -ftree-vectorizer-verbose=6 to do this (or -fopt-info-vec in newer versions of GCC), but I couldn't find anything similar for clang. Does clang support this or my only option is to peek in the disassembly ?

Answer 1

clang has following options to print diagnostics related to vectorization:

-Rpass=loop-vectorize identifies loops that were successfully vectorized.

-Rpass-missed=loop-vectorize identifies loops that failed vectorization and indicates if vectorization was specified.

-Rpass-analysis=loop-vectorize identifies the statements that caused vectorization to fail.

Source: http://llvm.org/docs/Vectorizers.html

Answer 2

Looking through the clang source code, there are a couple vectorization passes in Transforms/Vectorize:

• BBVectorize
• LoopVectorize
• SLPVectorize

The last three don't seem to have any arguments that will print things. But in inside BBVectorize there are a couple of options for printing things when clang is built debug:

• bb-vectorize-debug-instruction-examination - When debugging is enabled, output information on the instruction-examination process
• bb-vectorize-debug-candidate-selection - When debugging is enabled, output information on the candidate-selection process
• bb-vectorize-debug-pair-selection - When debugging is enabled, output information on the pair-selection process
• bb-vectorize-debug-cycle-check - When debugging is enabled, output information on the cycle-checking process
• bb-vectorize-debug-print-after-every-pair -When debugging is enabled, dump the basic block after every pair is fused

That looks like it's about it.