Revert "CodeGen: Allow small copyable blocks to "break" the CFG."
This reverts commit ada6595a526d71df04988eb0a4b4fe84df398ded.
This needs a simple probability check because there are some cases where it is
not profitable.
llvm-svn: 291695
diff --git a/llvm/lib/CodeGen/MachineBlockPlacement.cpp b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
index 42ae492..40e3840 100644
--- a/llvm/lib/CodeGen/MachineBlockPlacement.cpp
+++ b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
@@ -403,10 +403,6 @@
void buildCFGChains();
void optimizeBranches();
void alignBlocks();
- bool shouldTailDuplicate(MachineBasicBlock *BB);
- bool canTailDuplicateUnplacedPreds(
- MachineBasicBlock *BB, MachineBasicBlock *Succ,
- BlockChain &Chain, const BlockFilterSet *BlockFilter);
public:
static char ID; // Pass identification, replacement for typeid
@@ -565,45 +561,6 @@
return SuccProb;
}
-/// Check if a block should be tail duplicated.
-/// \p BB Block to check.
-bool MachineBlockPlacement::shouldTailDuplicate(MachineBasicBlock *BB) {
- // Blocks with single successors don't create additional fallthrough
- // opportunities. Don't duplicate them. TODO: When conditional exits are
- // analyzable, allow them to be duplicated.
- bool IsSimple = TailDup.isSimpleBB(BB);
-
- if (BB->succ_size() == 1)
- return false;
- return TailDup.shouldTailDuplicate(IsSimple, *BB);
-}
-
-/// When the option TailDupPlacement is on, this method checks if the
-/// fallthrough candidate block \p Succ (of block \p BB) can be tail-duplicated
-/// into all of its unplaced, unfiltered predecessors, that are not BB. In
-/// addition we keep a set of blocks that have been tail-duplicated into and
-/// allow those blocks to be unplaced as well. This allows the creation of a
-/// second (larger) spine and a short fallthrough spine.
-/// We also identify blocks with the CFG that would have been produced by
-/// tail-duplication and lay them out in the same manner.
-bool MachineBlockPlacement::canTailDuplicateUnplacedPreds(
- MachineBasicBlock *BB, MachineBasicBlock *Succ, BlockChain &Chain,
- const BlockFilterSet *BlockFilter) {
- if (!shouldTailDuplicate(Succ))
- return false;
-
- for (MachineBasicBlock *Pred : Succ->predecessors()) {
- // Make sure all unplaced and unfiltered predecessors can be
- // tail-duplicated into.
- if (Pred == BB || (BlockFilter && !BlockFilter->count(Pred))
- || BlockToChain[Pred] == &Chain)
- continue;
- if (!TailDup.canTailDuplicate(Succ, Pred))
- return false;
- }
- return true;
-}
-
/// When the option OutlineOptionalBranches is on, this method
/// checks if the fallthrough candidate block \p Succ (of block
/// \p BB) also has other unscheduled predecessor blocks which
@@ -677,12 +634,6 @@
if (SuccChain.UnscheduledPredecessors == 0)
return false;
- // As a heuristic, if we can duplicate the block into all its unscheduled
- // predecessors, we return false.
- if (TailDupPlacement
- && canTailDuplicateUnplacedPreds(BB, Succ, Chain, BlockFilter))
- return false;
-
// There are two basic scenarios here:
// -------------------------------------
// Case 1: triangular shape CFG (if-then):
@@ -1957,8 +1908,13 @@
DuplicatedToLPred = false;
DEBUG(dbgs() << "Redoing tail duplication for Succ#"
<< BB->getNumber() << "\n");
-
- if (!shouldTailDuplicate(BB))
+ bool IsSimple = TailDup.isSimpleBB(BB);
+ // Blocks with single successors don't create additional fallthrough
+ // opportunities. Don't duplicate them. TODO: When conditional exits are
+ // analyzable, allow them to be duplicated.
+ if (!IsSimple && BB->succ_size() == 1)
+ return false;
+ if (!TailDup.shouldTailDuplicate(IsSimple, *BB))
return false;
// This has to be a callback because none of it can be done after
// BB is deleted.
@@ -2011,7 +1967,6 @@
llvm::function_ref<void(MachineBasicBlock*)>(RemovalCallback);
SmallVector<MachineBasicBlock *, 8> DuplicatedPreds;
- bool IsSimple = TailDup.isSimpleBB(BB);
TailDup.tailDuplicateAndUpdate(IsSimple, BB, LPred,
&DuplicatedPreds, &RemovalCallbackRef);