[PATCH] D150664: MachineCombiner: use height in improvesCriticialPathLen()

[Shiva Chen via Phabricator via llvm-commits]

shiva0217 added a comment.

Theoretically, NewRootHeight and OldRootHeight should be equal.
Does it make sense to remove the Heights calculations?



================
Comment at: llvm/lib/CodeGen/MachineCombiner.cpp:269
+    MachineInstr *UseInstr = UI->getParent();
+    HeightOp = BlockTrace.getInstrCycles(*UseInstr).Height;
+    int DefIdx = DefInstr->findRegisterDefOperandIdx(MO.getReg());
----------------
In MachineTraceMetrics::Ensemble::computeInstrHeights function,  Loop header PHI heights are all 0.

It seems it could be addressed by defining.

    unsigned
    MachineTraceMetrics::Trace::getPHIHeight(const MachineInstr &PHI) const{
      // Loop header PHI heights are all 0.
      return TBI.Succ ? getInstrCycles(PHI).Height : 0;
    }


Repository:
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https://reviews.llvm.org/D150664