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

[Jay Foad 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++;
----------------
jayfoad wrote:

This is pretty horrible and I'm not sure it works.

**Either** leave liveins as a std::vector, in which case this code does not need to change.

**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.

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