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Correct dwarf unwind information in function epilogue for X86

Description

Correct dwarf unwind information in function epilogue for X86

This patch aims to provide correct dwarf unwind information in function
epilogue for X86.

It consists of two parts. The first part inserts CFI instructions that set
appropriate cfa offset and cfa register in emitEpilogue() in
X86FrameLowering. This part is X86 specific.

The second part is platform independent and ensures that:

  • CFI instructions do not affect code generation
  • Unwind information remains correct when a function is modified by different passes. This is done in a late pass by analyzing information about cfa offset and cfa register in BBs and inserting additional CFI directives where necessary.

Changed CFI instructions so that they:

  • are duplicable
  • are not counted as instructions when tail duplicating or tail merging
  • can be compared as equal

Added CFIInstrInserter pass:

  • analyzes each basic block to determine cfa offset and register valid at its entry and exit
  • verifies that outgoing cfa offset and register of predecessor blocks match incoming values of their successors
  • inserts additional CFI directives at basic block beginning to correct the rule for calculating CFA

Having CFI instructions in function epilogue can cause incorrect CFA
calculation rule for some basic blocks. This can happen if, due to basic
block reordering, or the existence of multiple epilogue blocks, some of the
blocks have wrong cfa offset and register values set by the epilogue block
above them.

CFIInstrInserter is currently run only on X86, but can be used by any target
that implements support for adding CFI instructions in epilogue.

Patch by Violeta Vukobrat.

Differential Revision: https://reviews.llvm.org/D35844

Details

Committed
petarjNov 1 2017, 9:04 AM
Differential Revision
D35844: Correct dwarf unwind information in function epilogue
Parents
rL317099: Add data formatter for libc++ std::queue
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