6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2025-06-14 14:24:05 +00:00
Code Issues Projects Releases Wiki Activity

Factor MergeBlockIntoPredecessor out into BasicBlockUtils.

Browse Source 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@53705 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson
2008-07-17 00:01:40 +00:00
parent 413907000e
commit b31b06d04b
3 changed files with 60 additions and 51 deletions
Download Patch File Download Diff File Expand all files Collapse all files

52
lib/Transforms/Utils/BasicBlockUtils.cpp
View File

@ -23,6 +23,58 @@
#include <algorithm>
using namespace llvm;
/// 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) {
// Can't merge the entry block.
if (pred_begin(BB) == pred_end(BB)) return false;
// Can't merge if there are multiple preds.
if (++pred_begin(BB) != pred_end(BB)) return false;
BasicBlock* PredBB = *pred_begin(BB);
// Can't merge if the edge is critical.
if (PredBB->getTerminator()->getNumSuccessors() != 1) return false;
// 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();
// Move all definitions in the successor to the predecessor...
PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
// Make all PHI nodes that referred to BB now refer to Pred as their
// source...
BB->replaceAllUsesWith(PredBB);
// Finally, erase the old block and update dominator info.
if (P) {
if (DominatorTree* DT = P->getAnalysisToUpdate<DominatorTree>()) {
DomTreeNode* DTN = DT->getNode(BB);
DomTreeNode* PredDTN = DT->getNode(PredBB);
if (DTN) {
SmallPtrSet<DomTreeNode*, 8> Children(DTN->begin(), DTN->end());
for (SmallPtrSet<DomTreeNode*, 8>::iterator DI = Children.begin(),
DE = Children.end(); DI != DE; ++DI)
DT->changeImmediateDominator(*DI, PredDTN);
DT->eraseNode(BB);
}
}
}
BB->eraseFromParent();
return true;
}
/// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)
/// with a value, then remove and delete the original instruction.
///