[PATCH] D142084: [RFC][X86][MemFold] Upgrade the mechanism of auto-generated Memory Folding Table

[Bing Yu via Phabricator via llvm-commits]

yubing added inline comments.


================
Comment at: llvm/utils/TableGen/X86FoldTablesEmitter.cpp:442
+    Result.CannotUnfold = BaseRegInst->isMoveReg ? true : Result.CannotUnfold;
+  } else if (RegInstr->isMoveReg && Result.IsStore)
     Result.CannotUnfold = true;
----------------
skan wrote:
> Why do we need `Result.IsStore` here?
load such as VMOVAPDZ128rm will never be unfolded.
if VMOVAPDZ128rm 's memoperand is invariant, then VMOVAPDZ128rm  will be hoisted directly and won't be unfolded into rm+rr
if VMOVAPDZ128rm 's memoperand is not invariant, we stop doing unfolding since compiler find it is a simple load.
```
  // First check whether we should hoist this instruction.
  if (!IsLoopInvariantInst(*MI) || !IsProfitableToHoist(*MI)) {
    // If not, try unfolding a hoistable load.
    MI = ExtractHoistableLoad(MI);
    if (!MI) return false;
  }
```
```
MachineInstr *MachineLICMBase::ExtractHoistableLoad(MachineInstr *MI) {
  // Don't unfold simple loads.
  if (MI->canFoldAsLoad())
    return nullptr;

```
@craig.topper , does line429~439 make sense to you as well?


Repository:
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  https://reviews.llvm.org/D142084/new/

https://reviews.llvm.org/D142084