[PATCH] D104612: [CGP][RISCV] Teach CodeGenPrepare::optimizeSwitchInst to honor isSExtCheaperThanZExt.

[Jessica Clarke via Phabricator via llvm-commits]

jrtc27 added inline comments.


================
Comment at: llvm/lib/CodeGen/CodeGenPrepare.cpp:7014-7016
+  // Some targets prefer SExt over ZExt, honor that.
+  if (TLI->isSExtCheaperThanZExt(OldVT, RegType))
+    ExtType = Instruction::SExt;
----------------
Do we not want to avoid this in the case this is a function argument that is already being zero-extended? i.e. something like:

```
  Instruction::CastOps ExtType = Instruction::CastOpsEnd;
  if (auto *Arg = dyn_cast<Argument>(Cond)) {
    if (Arg->hasSExtAttr())
      ExtType = Instruction::SExt;
    else if (Arg->hasZExtAttr())
      ExtType = Instruction::ZExt;
  }
  if (ExtType == Instruction::CastOpsEnd) {
    if (TLI->isSExtCheaperThanZExt(OldVT, RegType))
      ExtType = Instruction::SExt;
    else
      ExtType = Instruction::ZExt;
  }
```
(slightly abusing CastOpsEnd as being one past the last valid op, and thus a sentinel, though you could write it in other ways too if you wanted)



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  https://reviews.llvm.org/D104612/new/

https://reviews.llvm.org/D104612