Merge the enhancements from LoopUnroll's FoldBlockIntoPredecessor into
MergeBlockIntoPredecessor. This makes SimplifyCFG slightly more aggressive,
and makes it unnecessary for LoopUnroll to have its own copy of this code.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85667 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Utils/BasicBlockUtils.cpp b/lib/Transforms/Utils/BasicBlockUtils.cpp
index c2c662f..b6f00e2 100644
--- a/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -95,54 +95,28 @@
RecursivelyDeleteDeadPHINode(PN);
}
-/// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
-/// if possible. The return value indicates success or failure.
-bool llvm::MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P) {
- pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
- // Can't merge the entry block.
- if (pred_begin(BB) == pred_end(BB)) return false;
-
- BasicBlock *PredBB = *PI++;
- for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
- if (*PI != PredBB) {
- PredBB = 0; // There are multiple different predecessors...
- break;
- }
-
- // Can't merge if there are multiple predecessors.
- if (!PredBB) return false;
+/// MergeBlockIntoPredecessor - Folds a basic block into its predecessor if it
+/// only has one predecessor, and that predecessor only has one successor.
+/// If a Pass is given, the LoopInfo and DominatorTree analyses will be kept
+/// current. Returns the combined block, or null if no merging was performed.
+BasicBlock *llvm::MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P) {
+ // Don't merge if the block has multiple predecessors.
+ BasicBlock *PredBB = BB->getSinglePredecessor();
+ if (!PredBB) return 0;
+ // Don't merge if the predecessor has multiple successors.
+ if (PredBB->getTerminator()->getNumSuccessors() != 1) return 0;
// Don't break self-loops.
- if (PredBB == BB) return false;
+ if (PredBB == BB) return 0;
// Don't break invokes.
- if (isa<InvokeInst>(PredBB->getTerminator())) return false;
+ if (isa<InvokeInst>(PredBB->getTerminator())) return 0;
- succ_iterator SI(succ_begin(PredBB)), SE(succ_end(PredBB));
- BasicBlock* OnlySucc = BB;
- for (; SI != SE; ++SI)
- if (*SI != OnlySucc) {
- OnlySucc = 0; // There are multiple distinct successors!
- break;
- }
-
- // Can't merge if there are multiple successors.
- if (!OnlySucc) return false;
+ // Resolve any PHI nodes at the start of the block. They are all
+ // guaranteed to have exactly one entry if they exist, unless there are
+ // multiple duplicate (but guaranteed to be equal) entries for the
+ // incoming edges. This occurs when there are multiple edges from
+ // PredBB to BB.
+ FoldSingleEntryPHINodes(BB);
- // Can't merge if there is PHI loop.
- for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE; ++BI) {
- if (PHINode *PN = dyn_cast<PHINode>(BI)) {
- for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
- if (PN->getIncomingValue(i) == PN)
- return false;
- } else
- break;
- }
-
- // Begin by getting rid of unneeded PHIs.
- while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
- PN->replaceAllUsesWith(PN->getIncomingValue(0));
- BB->getInstList().pop_front(); // Delete the phi node...
- }
-
// Delete the unconditional branch from the predecessor...
PredBB->getInstList().pop_back();
@@ -153,7 +127,7 @@
// source...
BB->replaceAllUsesWith(PredBB);
- // Inherit predecessors name if it exists.
+ // If the predecessor doesn't have a name, take the successor's name.
if (!PredBB->hasName())
PredBB->takeName(BB);
@@ -172,12 +146,14 @@
DT->eraseNode(BB);
}
}
+ // Notify LoopInfo that the block is removed.
+ if (LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>())
+ LI->removeBlock(BB);
}
BB->eraseFromParent();
-
- return true;
+ return PredBB;
}
/// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)