[GlobalISel] Add G_SBFX + G_UBFX (bitfield extraction opcodes)

There is a bunch of similar bitfield extraction code throughout *ISelDAGToDAG.

E.g, ARMISelDAGToDAG, AArch64ISelDAGToDAG, and AMDGPUISelDAGToDAG all contain
code that matches a bitfield extract from an and + right shift.

Rather than duplicating code in the same way, this adds two opcodes:

- G_UBFX (unsigned bitfield extract)
- G_SBFX (signed bitfield extract)

They work like this

```
%x = G_UBFX %y, %lsb, %width
```

Where `lsb` and `width` are

- The least-significant bit of the extraction
- The width of the extraction

This will extract `width` bits from `%y`, starting at `lsb`. G_UBFX zero-extends
the result, while G_SBFX sign-extends the result.

This should allow us to use the combiner to match the bitfield extraction
patterns rather than duplicating pattern-matching code in each target.

Differential Revision: https://reviews.llvm.org/D98464

1 files changed, 11 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineVerifier.cpp b/llvm/lib/CodeGen/MachineVerifier.cpp
index 57eb944..af8b84e 100644
--- a/llvm/lib/CodeGen/MachineVerifier.cpp
+++ b/llvm/lib/CodeGen/MachineVerifier.cpp
@@ -1566,6 +1566,17 @@ void MachineVerifier::verifyPreISelGenericInstruction(const MachineInstr *MI) {
       report("Vector reduction requires vector source=", MI);
     break;
   }
+
+  case TargetOpcode::G_SBFX:
+  case TargetOpcode::G_UBFX: {
+    LLT DstTy = MRI->getType(MI->getOperand(0).getReg());
+    if (DstTy.isVector()) {
+      report("Bitfield extraction is not supported on vectors", MI);
+      break;
+    }
+    break;
+  }
+
   default:
     break;
   }