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/include/llvm/Transforms/Utils/BasicBlockUtils.h b/include/llvm/Transforms/Utils/BasicBlockUtils.h
index e766d72..47d6895 100644
--- a/include/llvm/Transforms/Utils/BasicBlockUtils.h
+++ b/include/llvm/Transforms/Utils/BasicBlockUtils.h
@@ -43,9 +43,11 @@
/// it is ultimately unused or if it reaches an unused cycle.
void DeleteDeadPHIs(BasicBlock *BB);
-/// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
-/// if possible. The return value indicates success or failure.
-bool MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P = 0);
+/// 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 *MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P = 0);
// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)
// with a value, then remove and delete the original instruction.
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)
diff --git a/lib/Transforms/Utils/LoopUnroll.cpp b/lib/Transforms/Utils/LoopUnroll.cpp
index d68427a..9b68df0 100644
--- a/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/lib/Transforms/Utils/LoopUnroll.cpp
@@ -49,52 +49,6 @@
}
}
-/// FoldBlockIntoPredecessor - Folds a basic block into its predecessor if it
-/// only has one predecessor, and that predecessor only has one successor.
-/// The LoopInfo Analysis that is passed will be kept consistent.
-/// Returns the new combined block.
-static BasicBlock *FoldBlockIntoPredecessor(BasicBlock *BB, LoopInfo* LI) {
- // Merge basic blocks into their predecessor if there is only one distinct
- // pred, and if there is only one distinct successor of the predecessor, and
- // if there are no PHI nodes.
- BasicBlock *OnlyPred = BB->getSinglePredecessor();
- if (!OnlyPred) return 0;
-
- if (OnlyPred->getTerminator()->getNumSuccessors() != 1)
- return 0;
-
- DEBUG(errs() << "Merging: " << *BB << "into: " << *OnlyPred);
-
- // 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
- // OnlyPred to OnlySucc.
- FoldSingleEntryPHINodes(BB);
-
- // Delete the unconditional branch from the predecessor...
- OnlyPred->getInstList().pop_back();
-
- // Move all definitions in the successor to the predecessor...
- OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList());
-
- // Make all PHI nodes that referred to BB now refer to Pred as their
- // source...
- BB->replaceAllUsesWith(OnlyPred);
-
- std::string OldName = BB->getName();
-
- // Erase basic block from the function...
- LI->removeBlock(BB);
- BB->eraseFromParent();
-
- // Inherit predecessor's name if it exists...
- if (!OldName.empty() && !OnlyPred->hasName())
- OnlyPred->setName(OldName);
-
- return OnlyPred;
-}
-
/// Unroll the given loop by Count. The loop must be in LCSSA form. Returns true
/// if unrolling was succesful, or false if the loop was unmodified. Unrolling
/// can only fail when the loop's latch block is not terminated by a conditional
@@ -333,7 +287,7 @@
} else {
Term->setUnconditionalDest(Dest);
// Merge adjacent basic blocks, if possible.
- if (BasicBlock *Fold = FoldBlockIntoPredecessor(Dest, LI)) {
+ if (BasicBlock *Fold = MergeBlockIntoPredecessor(Dest, LI)) {
std::replace(Latches.begin(), Latches.end(), Dest, Fold);
std::replace(Headers.begin(), Headers.end(), Dest, Fold);
}
diff --git a/test/Transforms/SimplifyCFG/PhiBlockMerge.ll b/test/Transforms/SimplifyCFG/PhiBlockMerge.ll
index a648efd..1219dfe 100644
--- a/test/Transforms/SimplifyCFG/PhiBlockMerge.ll
+++ b/test/Transforms/SimplifyCFG/PhiBlockMerge.ll
@@ -9,6 +9,7 @@
O: ; preds = %0
br i1 %b, label %N, label %Q
Q: ; preds = %O
+ call void @foo()
br label %N
N: ; preds = %Q, %O
; This block should be foldable into M
@@ -20,3 +21,4 @@
ret i32 %R
}
+declare void @foo()