[ARM] Remove unused class member in ARMConstantIslandPass

[statham-arm]

The map variable BlockJumpTableRefCount was added in commit f5f28d5 to track whether a basic block was the target of any jump table entries. This was used in the function fixupBTI to insert and remove BTIs after jump tables had been modified.

Commit 3b74224 removed fixupBTI on the grounds that the work was now being done elsewhere. That left BlockJumpTableRefCount still being created, but now nothing is using it. So we can garbage-collect that variable and all the code that populates it.

[llvmbot]

@llvm/pr-subscribers-backend-arm

Author: Simon Tatham (statham-arm)

Changes

The map variable BlockJumpTableRefCount was added in commit f5f28d5 to track whether a basic block was the target of any jump table entries. This was used in the function fixupBTI to insert and remove BTIs after jump tables had been modified.

Commit 3b74224 removed fixupBTI on the grounds that the work was now being done elsewhere. That left BlockJumpTableRefCount still being created, but now nothing is using it. So we can garbage-collect that variable and all the code that populates it.

---

Full diff: https://github.com/llvm/llvm-project/pull/141093.diff

1 Files Affected:

• (modified) llvm/lib/Target/ARM/ARMConstantIslandPass.cpp (-26)

diff --git a/llvm/lib/Target/ARM/ARMConstantIslandPass.cpp b/llvm/lib/Target/ARM/ARMConstantIslandPass.cpp
index 2972316fcee00..4b2fab2939af0 100644
--- a/llvm/lib/Target/ARM/ARMConstantIslandPass.cpp
+++ b/llvm/lib/Target/ARM/ARMConstantIslandPass.cpp
@@ -183,9 +183,6 @@ namespace {
     /// base address.
     DenseMap<int, int> JumpTableUserIndices;
 
-    // Maps a MachineBasicBlock to the number of jump tables entries.
-    DenseMap<const MachineBasicBlock *, int> BlockJumpTableRefCount;
-
     /// ImmBranch - One per immediate branch, keeping the machine instruction
     /// pointer, conditional or unconditional, the max displacement,
     /// and (if isCond is true) the corresponding unconditional branch
@@ -523,7 +520,6 @@ bool ARMConstantIslands::runOnMachineFunction(MachineFunction &mf) {
   CPEntries.clear();
   JumpTableEntryIndices.clear();
   JumpTableUserIndices.clear();
-  BlockJumpTableRefCount.clear();
   ImmBranches.clear();
   PushPopMIs.clear();
   T2JumpTables.clear();
@@ -736,14 +732,6 @@ Align ARMConstantIslands::getCPEAlign(const MachineInstr *CPEMI) {
   return MCP->getConstants()[CPI].getAlign();
 }
 
-// Exception landing pads, blocks that has their adress taken, and function
-// entry blocks will always be (potential) indirect jump targets, regardless of
-// whether they are referenced by or not by jump tables.
-static bool isAlwaysIndirectTarget(const MachineBasicBlock &MBB) {
-  return MBB.isEHPad() || MBB.hasAddressTaken() ||
-         &MBB == &MBB.getParent()->front();
-}
-
 /// scanFunctionJumpTables - Do a scan of the function, building up
 /// information about the sizes of each block and the locations of all
 /// the jump tables.
@@ -754,20 +742,6 @@ void ARMConstantIslands::scanFunctionJumpTables() {
           (I.getOpcode() == ARM::t2BR_JT || I.getOpcode() == ARM::tBR_JTr))
         T2JumpTables.push_back(&I);
   }
-
-  if (!MF->getInfo<ARMFunctionInfo>()->branchTargetEnforcement())
-    return;
-
-  if (const MachineJumpTableInfo *JTI = MF->getJumpTableInfo())
-    for (const MachineJumpTableEntry &JTE : JTI->getJumpTables())
-      for (const MachineBasicBlock *MBB : JTE.MBBs) {
-        if (isAlwaysIndirectTarget(*MBB))
-          // Set the reference count essentially to infinity, it will never
-          // reach zero and the BTI Instruction will never be removed.
-          BlockJumpTableRefCount[MBB] = std::numeric_limits<int>::max();
-        else
-          ++BlockJumpTableRefCount[MBB];
-      }
 }
 
 /// initializeFunctionInfo - Do the initial scan of the function, building up

[davemgreen]

LGTM