[PATCH] D152810: [RISCV] Fix IMPLICIT_DEF check in doPeepholeMaskedRVV

[Luke Lau via Phabricator via llvm-commits]

luke added inline comments.


================
Comment at: llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp:3188
   bool UseTUPseudo = false;
   if (RISCVII::hasVecPolicyOp(MaskedMCID.TSFlags)) {
     // Some operations are their own TU.
----------------
@reames The more I look at this the more confused I get, specifically this `hasVecPolicyOp` check here.
Looking at `computeInfoForInstr` in `RISCVInsertVSETVLI.cpp` would imply that if a `_MASK` pseudo doesn't have a policy operand, then it's implicitly tail undisturbed and mask undisturbed. 

However as you noted, if we don't a policy operand, then `UseTUPseudo` is set to false and we end up using `UnmaskedPseudo`, which is always tail undefined and mask undefined. And it doesn't have a merge operand, so we end up throwing away `N`'s merge operand without actually checking if it's implicit_def. Which would be incorrect?


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D152810/new/

https://reviews.llvm.org/D152810