[PATCH] D55967: [CodeExtractor] Do not extract unsafe lifetime markers

[Vedant Kumar via Phabricator via llvm-commits]

vsk created this revision.
vsk added reviewers: davidxl, kachkov98.
Herald added subscribers: hiraditya, eraman.

Lifetime markers which reference inputs to the extraction region are not
safe to extract. Example ('rhs' will be extracted):

    		entry:
    	      x = alloca
    	      y = alloca
           /              \
         lhs:             rhs:
  lifetime_start(x)   lifetime_start(x)
  use(x)    	      lifetime_start(y)
  lifetime_end(x)     use(x, y)
  lifetime_start(y)   lifetime_end(y)
  use(y)              lifetime_end(x)
  lifetime_end(y)     ...
  ...

Prior to extraction, the stack coloring pass sees that the slots for 'x'
and 'y' are in-use at the same time. After extraction, the coloring pass
infers that 'x' and 'y' are *not* in-use concurrently, because markers
from 'rhs' are no longer available to help decide otherwise.

This leads to a miscompile, because the stack slots actually are in-use
concurrently in the extracted function.

Fix this by moving lifetime start/end markers for memory regions defined
in the calling function around the call to the extracted function.

Fixes llvm.org/PR39671 (rdar://45939472).


https://reviews.llvm.org/D55967

Files:
  llvm/include/llvm/Transforms/Utils/CodeExtractor.h
  llvm/lib/Transforms/Utils/CodeExtractor.cpp
  llvm/test/Transforms/CodeExtractor/PartialInlineAlloca4.ll
  llvm/test/Transforms/CodeExtractor/PartialInlineAlloca5.ll
  llvm/test/Transforms/HotColdSplit/lifetime-markers-on-inputs.ll

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