[PATCH] D67500: [DebugInfo] LiveDebugValues: don't create transfer records for potentially invalid locations

[Jeremy Morse via Phabricator via llvm-commits]

jmorse created this revision.
jmorse added reviewers: aprantl, vsk, wolfgangp.
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This patch is the counter-part to D67393 <https://reviews.llvm.org/D67393>, and aims to solve the second problem mentioned there, that transfers which are found to be invalid after location propagation occurs should not be inserted. The solution is simple: just don't record transfers until the in-locations are all known to be correct, and then reprocess all instructions a final time creating transfers.

This involves touching every instruction in the program again, which is unfortunate, but an alternate implementation I wrote adds ~150 lines of code to try and unwind chains of transfers, involving a lot of additional complexity. IMO, this is a reasonable trade-off. As a bonus though, because we don't generate a transfer every time we look at a block, we don't generate redundant identical DBG_VALUEs if we re-visit a block.

There's a fractional reduction in scope-bytes-covered with this patch (<0.1%), all which must have been invalid.

(I'll have some asan-build-time measurements of this in a couple of hours).


Repository:
  rL LLVM

https://reviews.llvm.org/D67500

Files:
  lib/CodeGen/LiveDebugValues.cpp
  test/DebugInfo/MIR/X86/live-debug-values-bad-transfer.mir

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