[llvm] [ARM] Switch to LiveRegUnits to fix r7 register allocation bug (PR #84474)

[via llvm-commits]

https://github.com/AtariDreams updated https://github.com/llvm/llvm-project/pull/84474

>From 9054d3e85bc4563f7b28501b2044209fe51dd82b Mon Sep 17 00:00:00 2001
From: Rose <gfunni234 at gmail.com>
Date: Fri, 8 Mar 2024 07:59:02 -0500
Subject: [PATCH] [Thumb1] Switch to LiveRegUnits

---
 llvm/lib/Target/ARM/Thumb1FrameLowering.cpp | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/llvm/lib/Target/ARM/Thumb1FrameLowering.cpp b/llvm/lib/Target/ARM/Thumb1FrameLowering.cpp
index 0f4ece64bff532..047c6731333c9b 100644
--- a/llvm/lib/Target/ARM/Thumb1FrameLowering.cpp
+++ b/llvm/lib/Target/ARM/Thumb1FrameLowering.cpp
@@ -612,11 +612,11 @@ bool Thumb1FrameLowering::needPopSpecialFixUp(const MachineFunction &MF) const {
 
 static void findTemporariesForLR(const BitVector &GPRsNoLRSP,
                                  const BitVector &PopFriendly,
-                                 const LivePhysRegs &UsedRegs, unsigned &PopReg,
+                                 const LiveRegUnits &UsedRegs, unsigned &PopReg,
                                  unsigned &TmpReg, MachineRegisterInfo &MRI) {
   PopReg = TmpReg = 0;
   for (auto Reg : GPRsNoLRSP.set_bits()) {
-    if (UsedRegs.available(MRI, Reg)) {
+    if (UsedRegs.available(Reg)) {
       // Remember the first pop-friendly register and exit.
       if (PopFriendly.test(Reg)) {
         PopReg = Reg;
@@ -684,7 +684,7 @@ bool Thumb1FrameLowering::emitPopSpecialFixUp(MachineBasicBlock &MBB,
   // Look for a temporary register to use.
   // First, compute the liveness information.
   const TargetRegisterInfo &TRI = *STI.getRegisterInfo();
-  LivePhysRegs UsedRegs(TRI);
+  LiveRegUnits UsedRegs(TRI);
   UsedRegs.addLiveOuts(MBB);
   // The semantic of pristines changed recently and now,
   // the callee-saved registers that are touched in the function
@@ -710,11 +710,6 @@ bool Thumb1FrameLowering::emitPopSpecialFixUp(MachineBasicBlock &MBB,
   unsigned TemporaryReg = 0;
   BitVector PopFriendly =
       TRI.getAllocatableSet(MF, TRI.getRegClass(ARM::tGPRRegClassID));
-  // R7 may be used as a frame pointer, hence marked as not generally
-  // allocatable, however there's no reason to not use it as a temporary for
-  // restoring LR.
-  if (STI.getFramePointerReg() == ARM::R7)
-    PopFriendly.set(ARM::R7);
 
   assert(PopFriendly.any() && "No allocatable pop-friendly register?!");
   // Rebuild the GPRs from the high registers because they are removed