[PATCH] D70672: [DebugInfo] Don't sink DBG_VALUEs past other DBG_VALUEs of the same variable location

[Jeremy Morse via Phabricator via llvm-commits]

jmorse created this revision.
jmorse added reviewers: aprantl, vsk, bjope.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.

This patch is part of a fix for PR43855 [0], resolving problems in D58386 <https://reviews.llvm.org/D58386> / rGf5e1b718a6 <https://reviews.llvm.org/rGf5e1b718a675a4449b71423f04d38e1e93045105> (which ended up being backed out).

It turns out DBG_VALUEs would be sunk even if the variables location was re-specified in the block, so for example in:

   %0 = someinst
  DBG_VALUE %0, !123, !DIExpression()
   %1 = anotherinst
  DBG_VALUE %1, !123, !DIExpression()

if %0 were to sink, the corresponding DBG_VALUE would sink too, past the next DBG_VALUE, effectively re-ordering assignments.

To fix these things: I've added a SeenDbgVars set recording what variable locations have been seen in a block already (working bottom up), and now flag DBG_VALUEs that would pass a later DBG_VALUE for the same variable.

If such a DBG_VALUE has its operand sunk, then it will now be set to undef, if it can't be copy propagated. I've split out the copy-prop code into a helper function to ease this. This patch is based on a tree with f5e1b718a6 reapplied to make it easier to read.

NB, this only works for repeated DBG_VALUEs in the same basic block, the general case involving control flow is much harder, which I've written up in [1].

[0] https://bugs.llvm.org/show_bug.cgi?id=43855
[1] https://bugs.llvm.org/show_bug.cgi?id=44117


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D70672

Files:
  llvm/lib/CodeGen/MachineSink.cpp
  llvm/test/DebugInfo/MIR/X86/machinesink.mir

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