[llvm] RegAllocFast: Fix verifier errors after assigning to reserved registers (PR #128155)

[Carl Ritson via llvm-commits]

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@@ -1215,16 +1218,30 @@ MCPhysReg RegAllocFastImpl::getErrorAssignment(const LiveReg &LR,
 /// Changes operand OpNum in MI the refer the PhysReg, considering subregs.
 /// \return true if MI's MachineOperands were re-arranged/invalidated.
 bool RegAllocFastImpl::setPhysReg(MachineInstr &MI, MachineOperand &MO,
-                                  MCPhysReg PhysReg) {
+                                  const LiveReg &Assignment) {
+  MCPhysReg PhysReg = Assignment.PhysReg;
+
+  assert(PhysReg);
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perlfu wrote:

Should this assertion be here, given that !PhysReg is handled below?

https://github.com/llvm/llvm-project/pull/128155