// cannot because all branches may not be analyzable.
// E.g., the target may be able to remove an unconditional branch to
// a fallthrough when it occurs after predicated terminators.
+ SmallVector<MachineBasicBlock*, 4> EmptyBB;
for (MachineBasicBlock *ChainBB : FunctionChain) {
Cond.clear();
MachineBasicBlock *TBB = nullptr, *FBB = nullptr; // For AnalyzeBranch.
TII->removeBranch(*ChainBB);
TII->insertBranch(*ChainBB, FBB, TBB, Cond, dl);
ChainBB->updateTerminator();
+ } else if (Cond.empty() && TBB && ChainBB != TBB &&
+ !TBB->canFallThrough()) {
+ // When ChainBB is unconditional branch to the TBB, and TBB has no
+ // fallthrough predecessor and fallthrough successor, try to merge
+ // ChainBB and TBB. This is legal under the one of following conditions:
+ // 1. ChainBB is empty except for an unconditional branch.
+ // 2. TBB has only one predecessor.
+ MachineFunction::iterator I(TBB);
+ if (((TBB == &*F->begin()) || !std::prev(I)->canFallThrough()) &&
+ (TailDup.isSimpleBB(ChainBB) || (TBB->pred_size() == 1))) {
+ TII->removeBranch(*ChainBB);
+ ChainBB->removeSuccessor(TBB);
+
+ // Update the CFG.
+ for (MachineBasicBlock::pred_iterator PI = TBB->pred_begin(),
+ PE = TBB->pred_end(); PI != PE; PI++)
+ (*PI)->ReplaceUsesOfBlockWith(TBB, ChainBB);
+
+ for (MachineBasicBlock *Succ : TBB->successors())
+ ChainBB->addSuccessor(Succ, MBPI->getEdgeProbability(TBB, Succ));
+
+ // Move all the instructions of TBB to ChainBB.
+ ChainBB->splice(ChainBB->end(), TBB, TBB->begin(), TBB->end());
+ EmptyBB.push_back(TBB);
+ }
}
}
}
+
+ for (auto BB: EmptyBB) {
+ MLI->removeBlock(BB);
+ FunctionChain.remove(BB);
+ BlockToChain.erase(BB);
+ F->erase(BB);
+ }
}
void MachineBlockPlacement::alignBlocks() {
}
}
+ // optimizeBranches() may change the blocks, but we haven't updated the
+ // post-dominator tree. Because the post-dominator tree won't be used after
+ // this function and this pass don't preserve the post-dominator tree.
optimizeBranches();
alignBlocks();
BLR8 implicit $lr8, implicit $rm, implicit killed $x3
; CHECK: bb.5.if.else.i:
- ; CHECK: successors: %bb.11(0x80000000)
- ; CHECK: B %bb.11
+ ; CHECK-NEXT: renamable $x3 = LI8 1
+ ; CHECK-NEXT: BLR8 implicit $lr8, implicit $rm, implicit killed $x3
; CHECK: bb.8.while.body.i (align 4):
- ; CHECK: successors: %bb.11(0x04000000), %bb.9(0x7c000000)
- ; CHECK: BCC 76, killed renamable $cr0, %bb.11
-
- ; CHECK: bb.11:
- ; CHECK: renamable $x3 = LI8 1
- ; CHECK-NEXT: BLR8 implicit $lr8, implicit $rm, implicit killed $x3
+ ; CHECK: successors: %bb.5(0x04000000), %bb.9(0x7c000000)
+ ; CHECK: BCC 76, killed renamable $cr0, %bb.5
...