[llvm] Greedy: Take copy hints involving subregisters (PR #159570)

[Jay Foad via llvm-commits]

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@@ -2387,19 +2387,42 @@ void RAGreedy::initializeCSRCost() {
 /// The results are stored into \p Out.
 /// \p Out is not cleared before being populated.
 void RAGreedy::collectHintInfo(Register Reg, HintsInfo &Out) {
+  const TargetRegisterClass *RC = MRI->getRegClass(Reg);
+
   for (const MachineInstr &Instr : MRI->reg_nodbg_instructions(Reg)) {
-    if (!TII->isFullCopyInstr(Instr))
+    if (!Instr.isCopy())
       continue;
+
     // Look for the other end of the copy.
     Register OtherReg = Instr.getOperand(0).getReg();
+    unsigned OtherSubReg = Instr.getOperand(0).getSubReg();
+    unsigned SubReg = Instr.getOperand(1).getSubReg();
+
     if (OtherReg == Reg) {
       OtherReg = Instr.getOperand(1).getReg();
+      OtherSubReg = Instr.getOperand(1).getSubReg();
+      SubReg = Instr.getOperand(0).getSubReg();
       if (OtherReg == Reg)
         continue;
     }
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jayfoad wrote:

This is starting to look ugly so I created #159724 to try to simplify it.

https://github.com/llvm/llvm-project/pull/159570