[PATCH] D52921: [LiveDebugValues] Extend var ranges through artificial blocks

[Vedant Kumar via Phabricator via llvm-commits]

vsk created this revision.
vsk added reviewers: sdesmalen, aprantl, NikolaPrica.
Herald added a reviewer: javed.absar.
Herald added a subscriber: hiraditya.

ASan often introduces basic blocks consisting exclusively of
instructions without debug locations, or with line 0 debug locations.

LiveDebugValues needs to extend variable ranges through these artificial
blocks. Otherwise, a lot of variables disappear -- even at -O0.

Typically, LiveDebugValues does not extend a variable's range into a
block unless the block is essentially "part of" the variable's scope
(for a precise definition, see LexicalScopes::dominates). This patch
relaxes the lexical dominance check for artificial blocks.

This makes the following Swift program debuggable at -O0:

  1| var x = 100
  2| print("x = \(x)")

rdar://39127144


https://reviews.llvm.org/D52921

Files:
  llvm/lib/CodeGen/LiveDebugValues.cpp
  llvm/test/DebugInfo/AArch64/compiler-gen-bbs-livedebugvalues.ll

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