Revert "[AArch64][CodeGen] Avoid inverting hot branches during relaxation"

This reverts commit 46d2d7599d9ed5e68fb53e910feb10d47ee2667b.
Breaks build https://lab.llvm.org/buildbot/#/builders/21/builds/78779

1 files changed, 2 insertions, 61 deletions

diff --git a/llvm/lib/CodeGen/BranchRelaxation.cpp b/llvm/lib/CodeGen/BranchRelaxation.cpp
index 2995732..378f8bf 100644
--- a/llvm/lib/CodeGen/BranchRelaxation.cpp
+++ b/llvm/lib/CodeGen/BranchRelaxation.cpp
@@ -79,10 +79,6 @@ class BranchRelaxation : public MachineFunctionPass {
   };
 
   SmallVector<BasicBlockInfo, 16> BlockInfo;
-
-  // The basic block after which trampolines are inserted. This is the last
-  // basic block that isn't in the cold section.
-  MachineBasicBlock *TrampolineInsertionPoint = nullptr;
   std::unique_ptr<RegScavenger> RS;
   LivePhysRegs LiveRegs;
 
@@ -170,27 +166,16 @@ LLVM_DUMP_METHOD void BranchRelaxation::dumpBBs() {
 void BranchRelaxation::scanFunction() {
   BlockInfo.clear();
   BlockInfo.resize(MF->getNumBlockIDs());
-  TrampolineInsertionPoint = nullptr;
 
   // First thing, compute the size of all basic blocks, and see if the function
   // has any inline assembly in it. If so, we have to be conservative about
   // alignment assumptions, as we don't know for sure the size of any
-  // instructions in the inline assembly. At the same time, place the
-  // trampoline insertion point at the end of the hot portion of the function.
-  for (MachineBasicBlock &MBB : *MF) {
+  // instructions in the inline assembly.
+  for (MachineBasicBlock &MBB : *MF)
     BlockInfo[MBB.getNumber()].Size = computeBlockSize(MBB);
 
-    if (MBB.getSectionID() != MBBSectionID::ColdSectionID)
-      TrampolineInsertionPoint = &MBB;
-  }
-
   // Compute block offsets and known bits.
   adjustBlockOffsets(*MF->begin());
-
-  if (TrampolineInsertionPoint == nullptr) {
-    LLVM_DEBUG(dbgs() << "  No suitable trampoline insertion point found in "
-                      << MF->getName() << ".\n");
-  }
 }
 
 /// computeBlockSize - Compute the size for MBB.
@@ -391,50 +376,6 @@ bool BranchRelaxation::fixupConditionalBranch(MachineInstr &MI) {
   assert(!Fail && "branches to be relaxed must be analyzable");
   (void)Fail;
 
-  // Since cross-section conditional branches to the cold section are rarely
-  // taken, try to avoid inverting the condition. Instead, add a "trampoline
-  // branch", which unconditionally branches to the branch destination. Place
-  // the trampoline branch at the end of the function and retarget the
-  // conditional branch to the trampoline.
-  // tbz L1
-  // =>
-  // tbz L1Trampoline
-  // ...
-  // L1Trampoline: b  L1
-  if (MBB->getSectionID() != TBB->getSectionID() &&
-      TBB->getSectionID() == MBBSectionID::ColdSectionID &&
-      TrampolineInsertionPoint != nullptr) {
-    // If the insertion point is out of range, we can't put a trampoline there.
-    NewBB =
-        createNewBlockAfter(*TrampolineInsertionPoint, MBB->getBasicBlock());
-
-    if (isBlockInRange(MI, *NewBB)) {
-      LLVM_DEBUG(dbgs() << "  Retarget destination to trampoline at "
-                        << NewBB->back());
-
-      insertUncondBranch(NewBB, TBB);
-
-      // Update the successor lists to include the trampoline.
-      MBB->replaceSuccessor(TBB, NewBB);
-      NewBB->addSuccessor(TBB);
-
-      // Replace branch in the current (MBB) block.
-      removeBranch(MBB);
-      insertBranch(MBB, NewBB, FBB, Cond);
-
-      TrampolineInsertionPoint = NewBB;
-      finalizeBlockChanges(MBB, NewBB);
-      return true;
-    }
-
-    LLVM_DEBUG(
-        dbgs() << "  Trampoline insertion point out of range for Bcc from "
-               << printMBBReference(*MBB) << " to " << printMBBReference(*TBB)
-               << ".\n");
-    TrampolineInsertionPoint->setIsEndSection(NewBB->isEndSection());
-    MF->erase(NewBB);
-  }
-
   // Add an unconditional branch to the destination and invert the branch
   // condition to jump over it:
   // tbz L1