[PATCH] D118453: [DebugInfo][InstrRef][NFC] Free resources at an earlier stage, to avoid double accounting

[Jeremy Morse via Phabricator via llvm-commits]

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This patch releases some memory from InstrRefBasedLDV earlier that it would otherwise. The underlying problem is:

- We store a big table of "live in values for each block",
- We translate that into DBG_VALUE instructions in each block,

And both exist in memory at the same time, which needlessly doubles that information. The most of what this patch does is: as we progressively translate live-in information into DBG_VALUEs, we free the variable-value / machine-value tracking information as we go, which significantly reduces peak memory.

Rolled into this patch too: once we've build the per-block-live-in information, call "clear" on the collection of VLocTracker objects. These store all the variable assignments that happen in a block, there's no need to keep that around once we've made use of them. Doing so exposes another flaw: it seems we were spuriously collecting all variable assignments for a second time, into the final blocks assignment records. Stop this by setting the "VTracker" field of InstrRefBasedLDV to null, and in a couple of locations fix the condition for recording some information.

As a final twiddle, change a DenseMap into a SmallDenseMap to avoid what might be an un-necessary initial allocation.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D118453

Files:
  llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
  llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.h

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