[Lldb-commits] [PATCH] D103588: [trace] Create a top-level instruction class

[Vedant Kumar via Phabricator via lldb-commits]

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I'm quite concerned about the design decision to represent a trace as a vector of TraceInstruction. This bakes considerations that appear to be specific to Facebook's usage of IntelPT way too deep into lldb's APIs, and isn't workable for our use cases.

At Apple, we use lldb to navigate instruction traces that contain billions of instructions. Allocating 16 bytes per instruction simply will not scale for our workflows. We require the in-memory overhead to be approximately 1-2 bits per instruction. I'm not familiar with how large IntelPT traces can get, but presumably (for long enough traces) you will encounter the same scaling problem.

What alternatives to the vector<TraceInstruction> representation have you considered? One idea might be to implement your program analyses on top of a generic interface for navigating forward/backward through a trace and extracting info about the instruction via a set of API calls; this leaves the actual in-memory representation of "TraceInstruction" unspecified.


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https://reviews.llvm.org/D103588