[LLVMdev] RFC: Binary format for instrumentation based profiling data (original) (raw)

Bob Wilson bob.wilson at apple.com
Thu Mar 13 15:57:04 PDT 2014

On Mar 13, 2014, at 2:14 PM, Diego Novillo <dnovillo at google.com> wrote:

On Thu, Mar 13, 2014 at 11:51 AM, Bob Wilson <bob.wilson at apple.com> wrote:

On Mar 13, 2014, at 5:48 AM, Diego Novillo <dnovillo at google.com> wrote:

How are counters represented? Are these line numbers together with the counter? Basic blocks? Edges? There are no line numbers, basic blocks, or edges. It is just a sequence of counters that the front-end knows how to map to the code (the same as with our current textual file format). Sorry, you lost me. How exactly does the FE map them to the code? In the sample profiler, each instrumented line consists of a line offset, a discriminator (to distinguish distinct control flow paths on the same line) and the counter. We match them by computing the absolute line number from the offset and assign the counter to the corresponding basic block.

This is a proposal for the instrumentation-based approach that I talked about at the dev meeting. I don’t see how it can share the a file format with the sample profiler, since the content is fundamentally different.

I think we should be able to use the same pass in lib/Transforms/Scalar/SampleProfile.cpp to read profiles generated from instrumentation. The information is basically the same, so a bit of generalization of that code should be all we need to pass those counters down into the analysis module.

?? The information is completely different.

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