[PATCH] D123577: [MIPS][SelectionDAG] Enable TargetLowering::hasBitTest for masks that fit in ANDI.

[Simon Dardis via Phabricator via llvm-commits]

sdardis added inline comments.


================
Comment at: llvm/lib/Target/Mips/MipsISelLowering.cpp:1178
+bool MipsTargetLowering::hasBitTest(SDValue X, SDValue Y) const {
+  // We can use ANDI+SLTIU as a bit test. Y contains the bit position.
+  auto *C = dyn_cast<ConstantSDNode>(Y);
----------------
Add a comment here:

```
// For MIPSR2 or later, we may be able to use the `ext` instruction or its' double-word variants.
```


================
Comment at: llvm/lib/Target/Mips/MipsISelLowering.cpp:1179
+  // We can use ANDI+SLTIU as a bit test. Y contains the bit position.
+  auto *C = dyn_cast<ConstantSDNode>(Y);
+  return C && C->getAPIntValue().ule(14);
----------------
I believe this code would be clearer if it was the likes of:


```
  if (auto *C = dyn_Cast<ConstantSDNode>(Y))
    return C->getAPIntValue().ule(14);

  return false; 
```

Also, the `14` should be `15` here. `andi` takes a 16-bit immediate.




CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D123577/new/

https://reviews.llvm.org/D123577