[llvm] [X86] Convert X86FixupBWInsts from LivePhysRegs to LiveRegUnits. NFCI. (PR #65592)

[Jay Foad via llvm-commits]

================
@@ -202,22 +202,22 @@ Register FixupBWInstPass::getSuperRegDestIfDead(MachineInstr *OrigMI) const {
   if (SubRegIdx == X86::sub_8bit_hi)
     return Register();
 
-  // If neither the destination-super register nor any applicable subregisters
-  // are live after this instruction, then the super register is safe to use.
-  if (!LiveRegs.contains(SuperDestReg)) {
-    // If the original destination register was not the low 8-bit subregister
-    // then the super register check is sufficient.
-    if (SubRegIdx != X86::sub_8bit)
-      return SuperDestReg;
-    // If the original destination register was the low 8-bit subregister and
-    // we also need to check the 16-bit subregister and the high 8-bit
-    // subregister.
-    MCRegister HighReg = getX86SubSuperRegister(SuperDestReg, 8, /*High=*/true);
-    if (!LiveRegs.contains(getX86SubSuperRegister(OrigDestReg, 16)) &&
-        (!HighReg.isValid() || !LiveRegs.contains(HighReg)))
-      return SuperDestReg;
-    // Otherwise, we have a little more checking to do.
+  // Test all regunits of the super register that are not part of the
+  // sub register. If none of them are live then the super register is safe to
+  // use.
+  bool SuperIsLive = false;
+  auto Range = TRI->regunits(OrigDestReg);
+  MCRegUnitIterator I = Range.begin(), E = Range.end();
+  for (MCRegUnit S : TRI->regunits(SuperDestReg)) {
+    while (I != E && *I < S)
+      ++I;
+    if ((I == E || *I > S) && LiveUnits.getBitVector().test(S)) {
----------------
jayfoad wrote:

Yup - at least with std::lower_bound.

https://github.com/llvm/llvm-project/pull/65592