Ahmed Bougacha 15b3e8a93a [GlobalISel] Update DBG_VALUEs referencing DCE'd instructions. ...

Quentin points out that r298358 would cause us to emit different code
with debug info.  That's a big no-no; also erase the instructions that
only live thanks to DBG_VALUE users.

Adrian explained how this is an existing problem and an OK thing to do:
clang has allocas for all variables so shouldn't be affected at -O0, but
swift uses a bit of inlineasm to explicitly keep values live for the
purpose of debug info quality.  I'm not sure there is a better scheme.

llvm-svn: 298460

2017-03-21 23:42:54 +00:00

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