#define DEBUG_TYPE "simplifycfg"
#include "llvm/Transforms/Scalar.h"
-#include "llvm/Transforms/Utils/Local.h"
-#include "llvm/Constants.h"
-#include "llvm/Instructions.h"
-#include "llvm/Module.h"
-#include "llvm/Attributes.h"
-#include "llvm/Support/CFG.h"
-#include "llvm/Pass.h"
-#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/IR/Attributes.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
STATISTIC(NumSimpl, "Number of blocks simplified");
namespace {
- struct CFGSimplifyPass : public FunctionPass {
- static char ID; // Pass identification, replacement for typeid
- CFGSimplifyPass() : FunctionPass(&ID) {}
+struct CFGSimplifyPass : public FunctionPass {
+ static char ID; // Pass identification, replacement for typeid
+ CFGSimplifyPass() : FunctionPass(ID) {
+ initializeCFGSimplifyPassPass(*PassRegistry::getPassRegistry());
+ }
+ bool runOnFunction(Function &F) override;
- virtual bool runOnFunction(Function &F);
- };
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.addRequired<TargetTransformInfo>();
+ }
+};
}
char CFGSimplifyPass::ID = 0;
-static RegisterPass<CFGSimplifyPass> X("simplifycfg", "Simplify the CFG");
+INITIALIZE_PASS_BEGIN(CFGSimplifyPass, "simplifycfg", "Simplify the CFG", false,
+ false)
+INITIALIZE_AG_DEPENDENCY(TargetTransformInfo)
+INITIALIZE_PASS_END(CFGSimplifyPass, "simplifycfg", "Simplify the CFG", false,
+ false)
// Public interface to the CFGSimplification pass
FunctionPass *llvm::createCFGSimplificationPass() {
return new CFGSimplifyPass();
}
-/// ChangeToUnreachable - Insert an unreachable instruction before the specified
-/// instruction, making it and the rest of the code in the block dead.
-static void ChangeToUnreachable(Instruction *I) {
- BasicBlock *BB = I->getParent();
- // Loop over all of the successors, removing BB's entry from any PHI
- // nodes.
- for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
- (*SI)->removePredecessor(BB);
-
- new UnreachableInst(I->getContext(), I);
-
- // All instructions after this are dead.
- BasicBlock::iterator BBI = I, BBE = BB->end();
- while (BBI != BBE) {
- if (!BBI->use_empty())
- BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
- BB->getInstList().erase(BBI++);
- }
-}
-
-/// ChangeToCall - Convert the specified invoke into a normal call.
-static void ChangeToCall(InvokeInst *II) {
- BasicBlock *BB = II->getParent();
- SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
- CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args.begin(),
- Args.end(), "", II);
- NewCall->takeName(II);
- NewCall->setCallingConv(II->getCallingConv());
- NewCall->setAttributes(II->getAttributes());
- II->replaceAllUsesWith(NewCall);
-
- // Follow the call by a branch to the normal destination.
- BranchInst::Create(II->getNormalDest(), II);
-
- // Update PHI nodes in the unwind destination
- II->getUnwindDest()->removePredecessor(BB);
- BB->getInstList().erase(II);
-}
-
-static bool MarkAliveBlocks(BasicBlock *BB,
- SmallPtrSet<BasicBlock*, 128> &Reachable) {
-
- SmallVector<BasicBlock*, 128> Worklist;
- Worklist.push_back(BB);
- bool Changed = false;
- while (!Worklist.empty()) {
- BB = Worklist.back();
- Worklist.pop_back();
-
- if (!Reachable.insert(BB))
- continue;
-
- // Do a quick scan of the basic block, turning any obviously unreachable
- // instructions into LLVM unreachable insts. The instruction combining pass
- // canonicalizes unreachable insts into stores to null or undef.
- for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E;++BBI){
- if (CallInst *CI = dyn_cast<CallInst>(BBI)) {
- if (CI->doesNotReturn()) {
- // If we found a call to a no-return function, insert an unreachable
- // instruction after it. Make sure there isn't *already* one there
- // though.
- ++BBI;
- if (!isa<UnreachableInst>(BBI)) {
- ChangeToUnreachable(BBI);
- Changed = true;
- }
- break;
- }
- }
-
- // Store to undef and store to null are undefined and used to signal that
- // they should be changed to unreachable by passes that can't modify the
- // CFG.
- if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
- Value *Ptr = SI->getOperand(1);
-
- if (isa<UndefValue>(Ptr) ||
- (isa<ConstantPointerNull>(Ptr) &&
- SI->getPointerAddressSpace() == 0)) {
- ChangeToUnreachable(SI);
- Changed = true;
- break;
- }
- }
- }
-
- // Turn invokes that call 'nounwind' functions into ordinary calls.
- if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator()))
- if (II->doesNotThrow()) {
- ChangeToCall(II);
- Changed = true;
- }
-
- Changed |= ConstantFoldTerminator(BB);
- for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
- Worklist.push_back(*SI);
- }
- return Changed;
-}
-
-/// RemoveUnreachableBlocksFromFn - Remove blocks that are not reachable, even
-/// if they are in a dead cycle. Return true if a change was made, false
-/// otherwise.
-static bool RemoveUnreachableBlocksFromFn(Function &F) {
- SmallPtrSet<BasicBlock*, 128> Reachable;
- bool Changed = MarkAliveBlocks(F.begin(), Reachable);
-
- // If there are unreachable blocks in the CFG...
- if (Reachable.size() == F.size())
- return Changed;
-
- assert(Reachable.size() < F.size());
- NumSimpl += F.size()-Reachable.size();
-
- // Loop over all of the basic blocks that are not reachable, dropping all of
- // their internal references...
- for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) {
- if (Reachable.count(BB))
- continue;
-
- for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
- if (Reachable.count(*SI))
- (*SI)->removePredecessor(BB);
- BB->dropAllReferences();
- }
-
- for (Function::iterator I = ++F.begin(); I != F.end();)
- if (!Reachable.count(I))
- I = F.getBasicBlockList().erase(I);
- else
- ++I;
-
- return true;
-}
-
-/// MergeEmptyReturnBlocks - If we have more than one empty (other than phi
+/// mergeEmptyReturnBlocks - If we have more than one empty (other than phi
/// node) return blocks, merge them together to promote recursive block merging.
-static bool MergeEmptyReturnBlocks(Function &F) {
+static bool mergeEmptyReturnBlocks(Function &F) {
bool Changed = false;
-
+
BasicBlock *RetBlock = 0;
-
+
// Scan all the blocks in the function, looking for empty return blocks.
for (Function::iterator BBI = F.begin(), E = F.end(); BBI != E; ) {
BasicBlock &BB = *BBI++;
-
+
// Only look at return blocks.
ReturnInst *Ret = dyn_cast<ReturnInst>(BB.getTerminator());
if (Ret == 0) continue;
-
+
// Only look at the block if it is empty or the only other thing in it is a
// single PHI node that is the operand to the return.
if (Ret != &BB.front()) {
// Check for something else in the block.
BasicBlock::iterator I = Ret;
--I;
- if (!isa<PHINode>(I) || I != BB.begin() ||
- Ret->getNumOperands() == 0 ||
- Ret->getOperand(0) != I)
+ // Skip over debug info.
+ while (isa<DbgInfoIntrinsic>(I) && I != BB.begin())
+ --I;
+ if (!isa<DbgInfoIntrinsic>(I) &&
+ (!isa<PHINode>(I) || I != BB.begin() ||
+ Ret->getNumOperands() == 0 ||
+ Ret->getOperand(0) != I))
continue;
}
-
+
// If this is the first returning block, remember it and keep going.
if (RetBlock == 0) {
RetBlock = &BB;
continue;
}
-
+
// Otherwise, we found a duplicate return block. Merge the two.
Changed = true;
-
+
// Case when there is no input to the return or when the returned values
// agree is trivial. Note that they can't agree if there are phis in the
// blocks.
if (Ret->getNumOperands() == 0 ||
- Ret->getOperand(0) ==
+ Ret->getOperand(0) ==
cast<ReturnInst>(RetBlock->getTerminator())->getOperand(0)) {
BB.replaceAllUsesWith(RetBlock);
BB.eraseFromParent();
continue;
}
-
+
// If the canonical return block has no PHI node, create one now.
PHINode *RetBlockPHI = dyn_cast<PHINode>(RetBlock->begin());
if (RetBlockPHI == 0) {
- Value *InVal = cast<ReturnInst>(RetBlock->begin())->getOperand(0);
- RetBlockPHI = PHINode::Create(Ret->getOperand(0)->getType(), "merge",
+ Value *InVal = cast<ReturnInst>(RetBlock->getTerminator())->getOperand(0);
+ pred_iterator PB = pred_begin(RetBlock), PE = pred_end(RetBlock);
+ RetBlockPHI = PHINode::Create(Ret->getOperand(0)->getType(),
+ std::distance(PB, PE), "merge",
&RetBlock->front());
-
- for (pred_iterator PI = pred_begin(RetBlock), E = pred_end(RetBlock);
- PI != E; ++PI)
+
+ for (pred_iterator PI = PB; PI != PE; ++PI)
RetBlockPHI->addIncoming(InVal, *PI);
RetBlock->getTerminator()->setOperand(0, RetBlockPHI);
}
-
+
// Turn BB into a block that just unconditionally branches to the return
// block. This handles the case when the two return blocks have a common
// predecessor but that return different things.
BB.getTerminator()->eraseFromParent();
BranchInst::Create(RetBlock, &BB);
}
-
+
return Changed;
}
-/// IterativeSimplifyCFG - Call SimplifyCFG on all the blocks in the function,
+/// iterativelySimplifyCFG - Call SimplifyCFG on all the blocks in the function,
/// iterating until no more changes are made.
-static bool IterativeSimplifyCFG(Function &F) {
+static bool iterativelySimplifyCFG(Function &F, const TargetTransformInfo &TTI,
+ const DataLayout *DL) {
bool Changed = false;
bool LocalChange = true;
while (LocalChange) {
LocalChange = false;
-
- // Loop over all of the basic blocks (except the first one) and remove them
- // if they are unneeded...
+
+ // Loop over all of the basic blocks and remove them if they are unneeded...
//
- for (Function::iterator BBIt = ++F.begin(); BBIt != F.end(); ) {
- if (SimplifyCFG(BBIt++)) {
+ for (Function::iterator BBIt = F.begin(); BBIt != F.end(); ) {
+ if (SimplifyCFG(BBIt++, TTI, DL)) {
LocalChange = true;
++NumSimpl;
}
// simplify the CFG.
//
bool CFGSimplifyPass::runOnFunction(Function &F) {
- bool EverChanged = RemoveUnreachableBlocksFromFn(F);
- EverChanged |= MergeEmptyReturnBlocks(F);
- EverChanged |= IterativeSimplifyCFG(F);
-
+ if (skipOptnoneFunction(F))
+ return false;
+
+ const TargetTransformInfo &TTI = getAnalysis<TargetTransformInfo>();
+ DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
+ const DataLayout *DL = DLP ? &DLP->getDataLayout() : 0;
+ bool EverChanged = removeUnreachableBlocks(F);
+ EverChanged |= mergeEmptyReturnBlocks(F);
+ EverChanged |= iterativelySimplifyCFG(F, TTI, DL);
+
// If neither pass changed anything, we're done.
if (!EverChanged) return false;
- // IterativeSimplifyCFG can (rarely) make some loops dead. If this happens,
- // RemoveUnreachableBlocksFromFn is needed to nuke them, which means we should
+ // iterativelySimplifyCFG can (rarely) make some loops dead. If this happens,
+ // removeUnreachableBlocks is needed to nuke them, which means we should
// iterate between the two optimizations. We structure the code like this to
- // avoid reruning IterativeSimplifyCFG if the second pass of
- // RemoveUnreachableBlocksFromFn doesn't do anything.
- if (!RemoveUnreachableBlocksFromFn(F))
+ // avoid reruning iterativelySimplifyCFG if the second pass of
+ // removeUnreachableBlocks doesn't do anything.
+ if (!removeUnreachableBlocks(F))
return true;
-
+
do {
- EverChanged = IterativeSimplifyCFG(F);
- EverChanged |= RemoveUnreachableBlocksFromFn(F);
+ EverChanged = iterativelySimplifyCFG(F, TTI, DL);
+ EverChanged |= removeUnreachableBlocks(F);
} while (EverChanged);
-
+
return true;
}