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Re-enable "[MachineCopyPropagation] Extend pass to do COPY source forwarding"

Description

Re-enable "[MachineCopyPropagation] Extend pass to do COPY source forwarding"

Issues addressed since original review:

  • Moved removal of dead instructions found by LiveIntervals::shrinkToUses() outside of loop iterating over instructions to avoid instructions being deleted while pointed to by iterator.
  • Fixed ARMLoadStoreOptimizer bug exposed by this change in r311907.
  • The pass no longer forwards COPYs to physical register uses, since doing so can break code that implicitly relies on the physical register number of the use.
  • The pass no longer forwards COPYs to undef uses, since doing so can break the machine verifier by creating LiveRanges that don't end on a use (since the undef operand is not considered a use).

    [MachineCopyPropagation] Extend pass to do COPY source forwarding

    This change extends MachineCopyPropagation to do COPY source forwarding.

    This change also extends the MachineCopyPropagation pass to be able to be run during register allocation, after physical registers have been assigned, but before the virtual registers have been re-written, which allows it to remove virtual register COPY LiveIntervals that become dead through the forwarding of all of their uses.

Details

Committed
gberrySep 1 2017, 7:27 AM
Parents
rL312327: [ELF] - Never call splitIntoPieces() twice. NFC.
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