forked from OSchip/llvm-project
370 lines
13 KiB
C++
370 lines
13 KiB
C++
//===-- BasicBlockUtils.cpp - BasicBlock Utilities -------------------------==//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This family of functions perform manipulations on basic blocks, and
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// instructions contained within basic blocks.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Function.h"
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#include "llvm/Instructions.h"
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#include "llvm/Constant.h"
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#include "llvm/Type.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/Dominators.h"
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#include <algorithm>
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using namespace llvm;
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/// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
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/// if possible. The return value indicates success or failure.
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bool llvm::MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P) {
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pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
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// Can't merge the entry block.
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if (pred_begin(BB) == pred_end(BB)) return false;
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BasicBlock *PredBB = *PI++;
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for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
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if (*PI != PredBB) {
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PredBB = 0; // There are multiple different predecessors...
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break;
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}
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// Can't merge if there are multiple predecessors.
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if (!PredBB) return false;
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// Don't break self-loops.
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if (PredBB == BB) return false;
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// Don't break invokes.
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if (isa<InvokeInst>(PredBB->getTerminator())) return false;
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succ_iterator SI(succ_begin(PredBB)), SE(succ_end(PredBB));
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BasicBlock* OnlySucc = BB;
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for (; SI != SE; ++SI)
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if (*SI != OnlySucc) {
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OnlySucc = 0; // There are multiple distinct successors!
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break;
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}
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// Can't merge if there are multiple successors.
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if (!OnlySucc) return false;
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// Can't merge if there is PHI loop.
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for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE; ++BI) {
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if (PHINode *PN = dyn_cast<PHINode>(BI)) {
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for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
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if (PN->getIncomingValue(i) == PN)
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return false;
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} else
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break;
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}
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// Begin by getting rid of unneeded PHIs.
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while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
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PN->replaceAllUsesWith(PN->getIncomingValue(0));
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BB->getInstList().pop_front(); // Delete the phi node...
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}
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// Delete the unconditional branch from the predecessor...
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PredBB->getInstList().pop_back();
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// Move all definitions in the successor to the predecessor...
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PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
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// Make all PHI nodes that referred to BB now refer to Pred as their
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// source...
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BB->replaceAllUsesWith(PredBB);
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// Inherit predecessors name if it exists.
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if (!PredBB->hasName())
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PredBB->takeName(BB);
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// Finally, erase the old block and update dominator info.
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if (P) {
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if (DominatorTree* DT = P->getAnalysisToUpdate<DominatorTree>()) {
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DomTreeNode* DTN = DT->getNode(BB);
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DomTreeNode* PredDTN = DT->getNode(PredBB);
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if (DTN) {
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SmallPtrSet<DomTreeNode*, 8> Children(DTN->begin(), DTN->end());
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for (SmallPtrSet<DomTreeNode*, 8>::iterator DI = Children.begin(),
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DE = Children.end(); DI != DE; ++DI)
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DT->changeImmediateDominator(*DI, PredDTN);
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DT->eraseNode(BB);
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}
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}
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}
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BB->eraseFromParent();
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return true;
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}
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/// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)
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/// with a value, then remove and delete the original instruction.
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///
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void llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL,
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BasicBlock::iterator &BI, Value *V) {
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Instruction &I = *BI;
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// Replaces all of the uses of the instruction with uses of the value
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I.replaceAllUsesWith(V);
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// Make sure to propagate a name if there is one already.
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if (I.hasName() && !V->hasName())
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V->takeName(&I);
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// Delete the unnecessary instruction now...
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BI = BIL.erase(BI);
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}
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/// ReplaceInstWithInst - Replace the instruction specified by BI with the
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/// instruction specified by I. The original instruction is deleted and BI is
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/// updated to point to the new instruction.
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///
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void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL,
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BasicBlock::iterator &BI, Instruction *I) {
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assert(I->getParent() == 0 &&
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"ReplaceInstWithInst: Instruction already inserted into basic block!");
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// Insert the new instruction into the basic block...
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BasicBlock::iterator New = BIL.insert(BI, I);
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// Replace all uses of the old instruction, and delete it.
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ReplaceInstWithValue(BIL, BI, I);
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// Move BI back to point to the newly inserted instruction
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BI = New;
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}
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/// ReplaceInstWithInst - Replace the instruction specified by From with the
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/// instruction specified by To.
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///
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void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) {
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BasicBlock::iterator BI(From);
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ReplaceInstWithInst(From->getParent()->getInstList(), BI, To);
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}
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/// RemoveSuccessor - Change the specified terminator instruction such that its
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/// successor SuccNum no longer exists. Because this reduces the outgoing
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/// degree of the current basic block, the actual terminator instruction itself
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/// may have to be changed. In the case where the last successor of the block
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/// is deleted, a return instruction is inserted in its place which can cause a
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/// surprising change in program behavior if it is not expected.
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///
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void llvm::RemoveSuccessor(TerminatorInst *TI, unsigned SuccNum) {
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assert(SuccNum < TI->getNumSuccessors() &&
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"Trying to remove a nonexistant successor!");
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// If our old successor block contains any PHI nodes, remove the entry in the
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// PHI nodes that comes from this branch...
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//
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BasicBlock *BB = TI->getParent();
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TI->getSuccessor(SuccNum)->removePredecessor(BB);
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TerminatorInst *NewTI = 0;
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switch (TI->getOpcode()) {
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case Instruction::Br:
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// If this is a conditional branch... convert to unconditional branch.
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if (TI->getNumSuccessors() == 2) {
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cast<BranchInst>(TI)->setUnconditionalDest(TI->getSuccessor(1-SuccNum));
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} else { // Otherwise convert to a return instruction...
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Value *RetVal = 0;
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// Create a value to return... if the function doesn't return null...
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if (BB->getParent()->getReturnType() != Type::VoidTy)
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RetVal = Constant::getNullValue(BB->getParent()->getReturnType());
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// Create the return...
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NewTI = ReturnInst::Create(RetVal);
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}
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break;
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case Instruction::Invoke: // Should convert to call
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case Instruction::Switch: // Should remove entry
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default:
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case Instruction::Ret: // Cannot happen, has no successors!
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assert(0 && "Unhandled terminator instruction type in RemoveSuccessor!");
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abort();
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}
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if (NewTI) // If it's a different instruction, replace.
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ReplaceInstWithInst(TI, NewTI);
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}
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/// SplitEdge - Split the edge connecting specified block. Pass P must
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/// not be NULL.
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BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, Pass *P) {
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TerminatorInst *LatchTerm = BB->getTerminator();
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unsigned SuccNum = 0;
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for (unsigned i = 0, e = LatchTerm->getNumSuccessors(); ; ++i) {
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assert(i != e && "Didn't find edge?");
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if (LatchTerm->getSuccessor(i) == Succ) {
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SuccNum = i;
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break;
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}
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}
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// If this is a critical edge, let SplitCriticalEdge do it.
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if (SplitCriticalEdge(BB->getTerminator(), SuccNum, P))
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return LatchTerm->getSuccessor(SuccNum);
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// If the edge isn't critical, then BB has a single successor or Succ has a
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// single pred. Split the block.
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BasicBlock::iterator SplitPoint;
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if (BasicBlock *SP = Succ->getSinglePredecessor()) {
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// If the successor only has a single pred, split the top of the successor
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// block.
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assert(SP == BB && "CFG broken");
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return SplitBlock(Succ, Succ->begin(), P);
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} else {
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// Otherwise, if BB has a single successor, split it at the bottom of the
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// block.
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assert(BB->getTerminator()->getNumSuccessors() == 1 &&
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"Should have a single succ!");
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return SplitBlock(BB, BB->getTerminator(), P);
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}
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}
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/// SplitBlock - Split the specified block at the specified instruction - every
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/// thing before SplitPt stays in Old and everything starting with SplitPt moves
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/// to a new block. The two blocks are joined by an unconditional branch and
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/// the loop info is updated.
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///
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BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P) {
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BasicBlock::iterator SplitIt = SplitPt;
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while (isa<PHINode>(SplitIt))
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++SplitIt;
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BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split");
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// The new block lives in whichever loop the old one did.
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if (LoopInfo* LI = P->getAnalysisToUpdate<LoopInfo>())
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if (Loop *L = LI->getLoopFor(Old))
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L->addBasicBlockToLoop(New, LI->getBase());
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if (DominatorTree *DT = P->getAnalysisToUpdate<DominatorTree>())
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{
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// Old dominates New. New node domiantes all other nodes dominated by Old.
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DomTreeNode *OldNode = DT->getNode(Old);
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std::vector<DomTreeNode *> Children;
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for (DomTreeNode::iterator I = OldNode->begin(), E = OldNode->end();
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I != E; ++I)
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Children.push_back(*I);
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DomTreeNode *NewNode = DT->addNewBlock(New,Old);
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for (std::vector<DomTreeNode *>::iterator I = Children.begin(),
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E = Children.end(); I != E; ++I)
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DT->changeImmediateDominator(*I, NewNode);
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}
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if (DominanceFrontier *DF = P->getAnalysisToUpdate<DominanceFrontier>())
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DF->splitBlock(Old);
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return New;
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}
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/// SplitBlockPredecessors - This method transforms BB by introducing a new
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/// basic block into the function, and moving some of the predecessors of BB to
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/// be predecessors of the new block. The new predecessors are indicated by the
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/// Preds array, which has NumPreds elements in it. The new block is given a
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/// suffix of 'Suffix'.
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///
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/// This currently updates the LLVM IR, AliasAnalysis, DominatorTree and
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/// DominanceFrontier, but no other analyses.
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BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
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BasicBlock *const *Preds,
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unsigned NumPreds, const char *Suffix,
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Pass *P) {
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// Create new basic block, insert right before the original block.
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BasicBlock *NewBB =
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BasicBlock::Create(BB->getName()+Suffix, BB->getParent(), BB);
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// The new block unconditionally branches to the old block.
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BranchInst *BI = BranchInst::Create(BB, NewBB);
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// Move the edges from Preds to point to NewBB instead of BB.
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for (unsigned i = 0; i != NumPreds; ++i)
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Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB);
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// Update dominator tree and dominator frontier if available.
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DominatorTree *DT = P ? P->getAnalysisToUpdate<DominatorTree>() : 0;
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if (DT)
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DT->splitBlock(NewBB);
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if (DominanceFrontier *DF = P ? P->getAnalysisToUpdate<DominanceFrontier>():0)
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DF->splitBlock(NewBB);
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AliasAnalysis *AA = P ? P->getAnalysisToUpdate<AliasAnalysis>() : 0;
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// Insert a new PHI node into NewBB for every PHI node in BB and that new PHI
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// node becomes an incoming value for BB's phi node. However, if the Preds
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// list is empty, we need to insert dummy entries into the PHI nodes in BB to
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// account for the newly created predecessor.
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if (NumPreds == 0) {
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// Insert dummy values as the incoming value.
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for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
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cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
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return NewBB;
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}
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// Otherwise, create a new PHI node in NewBB for each PHI node in BB.
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for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ) {
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PHINode *PN = cast<PHINode>(I++);
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// Check to see if all of the values coming in are the same. If so, we
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// don't need to create a new PHI node.
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Value *InVal = PN->getIncomingValueForBlock(Preds[0]);
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for (unsigned i = 1; i != NumPreds; ++i)
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if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
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InVal = 0;
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break;
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}
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if (InVal) {
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// If all incoming values for the new PHI would be the same, just don't
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// make a new PHI. Instead, just remove the incoming values from the old
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// PHI.
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for (unsigned i = 0; i != NumPreds; ++i)
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PN->removeIncomingValue(Preds[i], false);
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} else {
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// If the values coming into the block are not the same, we need a PHI.
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// Create the new PHI node, insert it into NewBB at the end of the block
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PHINode *NewPHI =
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PHINode::Create(PN->getType(), PN->getName()+".ph", BI);
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if (AA) AA->copyValue(PN, NewPHI);
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// Move all of the PHI values for 'Preds' to the new PHI.
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for (unsigned i = 0; i != NumPreds; ++i) {
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Value *V = PN->removeIncomingValue(Preds[i], false);
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NewPHI->addIncoming(V, Preds[i]);
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}
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InVal = NewPHI;
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}
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// Add an incoming value to the PHI node in the loop for the preheader
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// edge.
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PN->addIncoming(InVal, NewBB);
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// Check to see if we can eliminate this phi node.
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if (Value *V = PN->hasConstantValue(DT != 0)) {
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Instruction *I = dyn_cast<Instruction>(V);
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if (!I || DT == 0 || DT->dominates(I, PN)) {
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PN->replaceAllUsesWith(V);
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if (AA) AA->deleteValue(PN);
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PN->eraseFromParent();
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}
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}
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}
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return NewBB;
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}
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