Correct dwarf unwind information in function epilogue

Authored by petarj on Apr 24 2018, 3:32 AM.


Correct dwarf unwind information in function epilogue

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 (they are not counted as instructions when tail duplicating or tail merging)
  • 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.

Added CFIInstrInserter pass:

  • analyzes each basic block to determine cfa offset and register are 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/D42848

llvm-svn: 330706


petarjApr 24 2018, 3:32 AM
Differential Revision
D42848: Correct dwarf unwind information in function epilogue
rGfce722e6f87f: [mips] Correct the patterns for bswap