[llvm] [RISCV][GISel] Move G_BRJT expansion to legalization (PR #73711)

[Michael Maitland via llvm-commits]

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@@ -317,6 +318,62 @@ bool RISCVLegalizerInfo::legalizeShlAshrLshr(
   return true;
 }
 
+bool RISCVLegalizerInfo::legalizeBRJT(MachineInstr &MI,
+                                      MachineIRBuilder &MIRBuilder) const {
+  MachineRegisterInfo &MRI = *MIRBuilder.getMRI();
+  auto &MF = *MI.getParent()->getParent();
+  const MachineJumpTableInfo *MJTI = MF.getJumpTableInfo();
+  unsigned EntrySize = MJTI->getEntrySize(MF.getDataLayout());
+
+  Register PtrReg = MI.getOperand(0).getReg();
+  LLT PtrTy = MRI.getType(PtrReg);
+  Register IndexReg = MI.getOperand(2).getReg();
+  LLT IndexTy = MRI.getType(IndexReg);
+
+  MachineInstrBuilder Index;
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michaelmaitland wrote:

Should we change this to `Register Index` and do `Index = MIRBuilder.buildShl(IndexTy, IndexReg, ShiftAmt).getReg(0);` to avoid creating a new MachineInstrBuilder that is discarded by the assignment below? MachineInstrBuilder sounds like it would use more memory than a Register.

https://github.com/llvm/llvm-project/pull/73711