[llvm] [WIP][CodeGen] Modifying MBB's liveins representation as into regUnits (PR #129847)

[Vikash Gupta via llvm-commits]

================
@@ -597,54 +596,67 @@ void MachineBasicBlock::printAsOperand(raw_ostream &OS,
   printName(OS, 0);
 }
 
-void MachineBasicBlock::removeLiveIn(MCRegister Reg, LaneBitmask LaneMask) {
-  LiveInVector::iterator I = find_if(
-      LiveIns, [Reg](const RegisterMaskPair &LI) { return LI.PhysReg == Reg; });
-  if (I == LiveIns.end())
-    return;
+void MachineBasicBlock::addLiveIn(MCRegister PhysReg, LaneBitmask LaneMask) {
+  assert(PhysReg.isPhysical() && "live-in should be a physical register");
+  const TargetRegisterInfo *TRI = getParent()->getSubtarget().getRegisterInfo();
+  for (MCRegUnitMaskIterator U(PhysReg, TRI); U.isValid(); ++U) {
+    LaneBitmask Mask = (*U).second;
+    MCRegUnit Unit = (*U).first;
+    if ((Mask & LaneMask).any())
+      for (MCRegUnitRootIterator RootReg(Unit, TRI); RootReg.isValid();
+           ++RootReg)
+        LiveIns.insert(*RootReg);
+  }
+}
 
-  I->LaneMask &= ~LaneMask;
-  if (I->LaneMask.none())
-    LiveIns.erase(I);
+void MachineBasicBlock::removeLiveIn(MCRegister Reg, LaneBitmask LaneMask) {
+  assert(Reg.isPhysical() && "live-in should be a physical register");
+  const TargetRegisterInfo *TRI = getParent()->getSubtarget().getRegisterInfo();
+  for (MCRegUnitMaskIterator U(Reg, TRI); U.isValid(); ++U) {
+    LaneBitmask Mask = (*U).second;
+    MCRegUnit Unit = (*U).first;
+    if ((Mask & LaneMask).any())
+      for (MCRegUnitRootIterator RootReg(Unit, TRI); RootReg.isValid();
+           ++RootReg)
+        LiveIns.erase(*RootReg);
+  }
 }
 
 MachineBasicBlock::livein_iterator
 MachineBasicBlock::removeLiveIn(MachineBasicBlock::livein_iterator I) {
-  // Get non-const version of iterator.
-  LiveInVector::iterator LI = LiveIns.begin() + (I - LiveIns.begin());
-  return LiveIns.erase(LI);
+  if (I == LiveIns.end())
+    return I;
+
+  DenseSet<MCRegister>::iterator start = LiveIns.begin();
+  while (start != I)
+    start++;
+  MachineBasicBlock::livein_iterator next = start;
+  LiveIns.erase(start);
+  return next++;
----------------
vg0204 wrote:

Agreed!

> Or remove this method altogether. It is only used in one place, in X86FloatingPoint, and that code can ber rewritten to do this in some other way.

Does this alternative make sense using _**make_early_inc_range**_

```
static unsigned calcLiveInMask(MachineBasicBlock *MBB, bool RemoveFPs) {
  unsigned Mask = 0;
  for (auto &I : llvm::make_early_inc_range(MBB->liveins())) {
    MCPhysReg Reg = *I;
    static_assert(X86::FP6 - X86::FP0 == 6, "sequential regnums");
    if (Reg >= X86::FP0 && Reg <= X86::FP6) {
      Mask |= 1 << (Reg - X86::FP0);
      if (RemoveFPs) {
        MBB->removeLiveIn(I);
        continue;
      }
    }
  }
  return Mask;
}

```

https://github.com/llvm/llvm-project/pull/129847