[llvm] [CodeGen] Correctly handle non-standard cases in RemoveLoadsIntoFakeUses (PR #111551)

[Matt Arsenault via llvm-commits]

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@@ -143,13 +152,15 @@ bool RemoveLoadsIntoFakeUses::runOnMachineFunction(MachineFunction &MF) {
       // that register.
       if (!RegFakeUses.empty()) {
         for (const MachineOperand &MO : MI.operands()) {
-          if (MO.isReg() && MO.isDef()) {
-            Register Reg = MO.getReg();
-            assert(Reg.isPhysical() &&
-                   "VReg seen in function with NoVRegs set?");
-            for (MCRegUnit Unit : TRI->regunits(Reg))
-              RegFakeUses.erase(Unit);
-          }
+          if (!MO.isReg())
+            continue;
+          Register Reg = MO.getReg();
+          // We clear RegFakeUses for this register and all subregisters,
+          // because any such FAKE_USE encountered prior is no longer relevant
+          // for later encountered loads.
+          for (MachineInstr *&FakeUse : reverse(RegFakeUses))
+            if (!TRI->regsOverlap(Reg, FakeUse->getOperand(0).getReg()))
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arsenm wrote:

FakeUse->readsRegister 

https://github.com/llvm/llvm-project/pull/111551