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

Diego Novillo dnovillo at google.com
Fri Mar 14 05:40:10 PDT 2014

On Thu, Mar 13, 2014 at 9:19 PM, Justin Bogner <mail at justinbogner.com>wrote:

The instrumentation based profiling is done in the front end, and the counters are related to parts do the AST. Their isn't enough information for a backend pass to map them to anything. We feed block frequency and branch probability through metadata, much like the sampling based approach, but it happens during irgen in the front end, rather than in a backend pass.

Ah, OK. At least we get the annotations through to the backend. So, instrumentation gathers both block and edge weights? Or do you derive edge weights from blocks?

While it might be possible to translate the instrumentation format to the profile format, it wouldn't be possible to go the other way, and the translation would be imperfect.

I'm only interested in passing the instrumentation down to the back end. Are you folks thinking of doing other kinds of instrumentation? (value profiling, for example).

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