[ARM] Remove a redundant function fixupBTI

Since the redundant BTI instructions emitted by jump tables are now
removed in the ARMBranchTargets pass, the fixupBTI function is not needed
in the ARMConstantIslandPass. Some related tests are removed as well.

The relevant patch that removes the redundant BTI instructions:
https://reviews.llvm.org/D144470

Differential Revision: https://reviews.llvm.org/D145048

Author: Jirui Wu

llvm/lib/Target/ARM/ARMConstantIslandPass.cpp

@@ -277,8 +277,6 @@ namespace {
                               unsigned &DeadSize, bool &CanDeleteLEA,
                               bool &BaseRegKill);
     bool optimizeThumb2JumpTables();
-    void fixupBTI(unsigned JTI, MachineBasicBlock &OldBB,
-                  MachineBasicBlock &NewBB);
     MachineBasicBlock *adjustJTTargetBlockForward(unsigned JTI,
                                                   MachineBasicBlock *BB,
                                                   MachineBasicBlock *JTBB);
@@ -2455,38 +2453,6 @@ bool ARMConstantIslands::reorderThumb2JumpTables() {
   return MadeChange;
 }
 
-void ARMConstantIslands::fixupBTI(unsigned JTI, MachineBasicBlock &OldBB,
-                                  MachineBasicBlock &NewBB) {
-  assert(isThumb2 && "BTI in Thumb1?");
-
-  // Insert a BTI instruction into NewBB
-  BuildMI(NewBB, NewBB.begin(), DebugLoc(), TII->get(ARM::t2BTI));
-
-  // Update jump table reference counts.
-  const MachineJumpTableInfo &MJTI = *MF->getJumpTableInfo();
-  const MachineJumpTableEntry &JTE = MJTI.getJumpTables()[JTI];
-  for (const MachineBasicBlock *MBB : JTE.MBBs) {
-    if (MBB != &OldBB)
-      continue;
-    --BlockJumpTableRefCount[MBB];
-    ++BlockJumpTableRefCount[&NewBB];
-  }
-
-  // If the old basic block reference count dropped to zero, remove
-  // the BTI instruction at its beginning.
-  if (BlockJumpTableRefCount[&OldBB] > 0)
-    return;
-
-  // Skip meta instructions
-  auto BTIPos = llvm::find_if_not(OldBB.instrs(), [](const MachineInstr &MI) {
-    return MI.isMetaInstruction();
-  });
-  assert(BTIPos->getOpcode() == ARM::t2BTI &&
-         "BasicBlock is mentioned in a jump table but does start with BTI");
-  if (BTIPos->getOpcode() == ARM::t2BTI)
-    BTIPos->eraseFromParent();
-}
-
 MachineBasicBlock *ARMConstantIslands::adjustJTTargetBlockForward(
     unsigned JTI, MachineBasicBlock *BB, MachineBasicBlock *JTBB) {
   // If the destination block is terminated by an unconditional branch,
@@ -2546,9 +2512,6 @@ MachineBasicBlock *ARMConstantIslands::adjustJTTargetBlockForward(
   NewBB->addSuccessor(BB);
   JTBB->replaceSuccessor(BB, NewBB);
 
-  if (MF->getInfo<ARMFunctionInfo>()->branchTargetEnforcement())
-    fixupBTI(JTI, *BB, *NewBB);
-
   ++NumJTInserted;
   return NewBB;
 }