AMDPGU/R600: Replace llvm_unreachable() call with LLVMContext::emitError()

[• tstellarAMD]

Summary

This fixes an issue on MIPS where the infinite-loop-evegreen.ll test
was failing to terminate.

[dsanders]

This fixes the test for the Phase 2 and Phase 3 Release build for me. Thanks for the quick fix.

lib/Target/AMDGPU/AMDILCFGStructurizer.cpp

1735–1736

These two variables are unused now.

lib/Target/AMDGPU/AMDILCFGStructurizer.cpp

AMDGPUCFGStructurizer::normalizeInfiniteLoopExit(MachineLoop* LoopRep) {
   // Is LoopRep an infinite loop ?
   if (!BranchMI || !isUncondBranch(BranchMI))
     return nullptr;
 
   MachineBasicBlock *DummyExitBlk = FuncRep->CreateMachineBasicBlock();
   FuncRep->push_back(DummyExitBlk);  //insert to function
   SHOWNEWBLK(DummyExitBlk, "DummyExitBlock to normalize infiniteLoop: ");
   DEBUG(dbgs() << "Old branch instr: " << *BranchMI << "\n";);
   MachineBasicBlock::iterator I = BranchMI;
   unsigned ImmReg = FuncRep->getRegInfo().createVirtualRegister(I32RC);
-  llvm_unreachable("Extra register needed to handle CFG");
-  MachineInstr *NewMI = insertInstrBefore(I, AMDGPU::BRANCH_COND_i32);
-  MachineInstrBuilder MIB(*FuncRep, NewMI);
-  MIB.addMBB(LoopHeader);
-  MIB.addReg(ImmReg, false);
-  SHOWNEWINSTR(NewMI);
-  BranchMI->eraseFromParent();
-  LoopLatch->addSuccessor(DummyExitBlk);
-
-  return DummyExitBlk;
+  LLVMContext &Ctx = LoopHeader->getParent()->getFunction()->getContext();
+  Ctx.emitError("Extra register needed to handle CFG");
+  return nullptr;
 }
 
 void AMDGPUCFGStructurizer::removeUnconditionalBranch(MachineBasicBlock *MBB) {
   MachineInstr *BranchMI;
 
   // I saw two unconditional branch in one basic block in example
   // test_fc_do_while_or.c need to fix the upstream on this to remove the loop.
   while ((BranchMI = getLoopendBlockBranchInstr(MBB))