#include "llvm/Pass.h"
#include "llvm/Type.h"
#include "llvm/Support/CFG.h"
+#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include <map>
using namespace llvm;
STATISTIC(NumEliminated, "Number of unconditional branches eliminated");
+static cl::opt<unsigned>
+TailDupThreshold("taildup-threshold",
+ cl::desc("Max block size to tail duplicate"),
+ cl::init(1), cl::Hidden);
+
namespace {
- cl::opt<unsigned>
- Threshold("taildup-threshold", cl::desc("Max block size to tail duplicate"),
- cl::init(6), cl::Hidden);
class VISIBILITY_HIDDEN TailDup : public FunctionPass {
bool runOnFunction(Function &F);
public:
static char ID; // Pass identification, replacement for typeid
- TailDup() : FunctionPass((intptr_t)&ID) {}
+ TailDup() : FunctionPass(&ID) {}
private:
- inline bool shouldEliminateUnconditionalBranch(TerminatorInst *TI);
+ inline bool shouldEliminateUnconditionalBranch(TerminatorInst *, unsigned);
inline void eliminateUnconditionalBranch(BranchInst *BI);
+ SmallPtrSet<BasicBlock*, 4> CycleDetector;
};
- char TailDup::ID = 0;
- RegisterPass<TailDup> X("tailduplicate", "Tail Duplication");
}
+char TailDup::ID = 0;
+static RegisterPass<TailDup> X("tailduplicate", "Tail Duplication");
+
// Public interface to the Tail Duplication pass
FunctionPass *llvm::createTailDuplicationPass() { return new TailDup(); }
/// runOnFunction - Top level algorithm - Loop over each unconditional branch in
-/// the function, eliminating it if it looks attractive enough.
-///
+/// the function, eliminating it if it looks attractive enough. CycleDetector
+/// prevents infinite loops by checking that we aren't redirecting a branch to
+/// a place it already pointed to earlier; see PR 2323.
bool TailDup::runOnFunction(Function &F) {
bool Changed = false;
- for (Function::iterator I = F.begin(), E = F.end(); I != E; )
- if (shouldEliminateUnconditionalBranch(I->getTerminator())) {
+ CycleDetector.clear();
+ for (Function::iterator I = F.begin(), E = F.end(); I != E; ) {
+ if (shouldEliminateUnconditionalBranch(I->getTerminator(),
+ TailDupThreshold)) {
eliminateUnconditionalBranch(cast<BranchInst>(I->getTerminator()));
Changed = true;
} else {
++I;
+ CycleDetector.clear();
}
+ }
return Changed;
}
/// We don't count PHI nodes in the count since they will be removed when the
/// contents of the block are copied over.
///
-bool TailDup::shouldEliminateUnconditionalBranch(TerminatorInst *TI) {
+bool TailDup::shouldEliminateUnconditionalBranch(TerminatorInst *TI,
+ unsigned Threshold) {
BranchInst *BI = dyn_cast<BranchInst>(TI);
if (!BI || !BI->isUnconditional()) return false; // Not an uncond branch!
if (!DTI->use_empty())
return false;
- // Do not bother working on dead blocks...
- pred_iterator PI = pred_begin(Dest), PE = pred_end(Dest);
- if (PI == PE && Dest != Dest->getParent()->begin())
- return false; // It's just a dead block, ignore it...
-
- // Also, do not bother with blocks with only a single predecessor: simplify
+ // Do not bother with blocks with only a single predecessor: simplify
// CFG will fold these two blocks together!
+ pred_iterator PI = pred_begin(Dest), PE = pred_end(Dest);
++PI;
if (PI == PE) return false; // Exactly one predecessor!
- BasicBlock::iterator I = Dest->begin();
- while (isa<PHINode>(*I)) ++I;
+ BasicBlock::iterator I = Dest->getFirstNonPHI();
for (unsigned Size = 0; I != Dest->end(); ++I) {
if (Size == Threshold) return false; // The block is too large.
// Don't tail duplicate call instructions. They are very large compared to
// other instructions.
if (isa<CallInst>(I) || isa<InvokeInst>(I)) return false;
+
+ // Allso alloca and malloc.
+ if (isa<AllocationInst>(I)) return false;
+
+ // Some vector instructions can expand into a number of instructions.
+ if (isa<ShuffleVectorInst>(I) || isa<ExtractElementInst>(I) ||
+ isa<InsertElementInst>(I)) return false;
// Only count instructions that are not debugger intrinsics.
if (!isa<DbgInfoIntrinsic>(I)) ++Size;
if (TooMany-- == 0) return false;
}
- // Finally, if this unconditional branch is a fall-through, be careful about
+ // If this unconditional branch is a fall-through, be careful about
// tail duplicating it. In particular, we don't want to taildup it if the
// original block will still be there after taildup is completed: doing so
// would eliminate the fall-through, requiring unconditional branches.
}
}
+ // Finally, check that we haven't redirected to this target block earlier;
+ // there are cases where we loop forever if we don't check this (PR 2323).
+ if (!CycleDetector.insert(Dest))
+ return false;
+
return true;
}
// If there are non-phi instructions in DestBlock that have no operands
// defined in DestBlock, and if the instruction has no side effects, we can
// move the instruction to DomBlock instead of duplicating it.
- BasicBlock::iterator BBI = DestBlock->begin();
- while (isa<PHINode>(BBI)) ++BBI;
+ BasicBlock::iterator BBI = DestBlock->getFirstNonPHI();
while (!isa<TerminatorInst>(BBI)) {
Instruction *I = BBI++;
// this reason, we spill all values that are used outside of the tail to the
// stack.
for (BasicBlock::iterator I = DestBlock->begin(); I != DestBlock->end(); ++I)
- for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
- ++UI) {
- bool ShouldDemote = false;
- if (cast<Instruction>(*UI)->getParent() != DestBlock) {
- // We must allow our successors to use tail values in their PHI nodes
- // (if the incoming value corresponds to the tail block).
- if (PHINode *PN = dyn_cast<PHINode>(*UI)) {
- for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
- if (PN->getIncomingValue(i) == I &&
- PN->getIncomingBlock(i) != DestBlock) {
- ShouldDemote = true;
- break;
- }
-
- } else {
- ShouldDemote = true;
- }
- } else if (PHINode *PN = dyn_cast<PHINode>(cast<Instruction>(*UI))) {
- // If the user of this instruction is a PHI node in the current block,
- // which has an entry from another block using the value, spill it.
- for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
- if (PN->getIncomingValue(i) == I &&
- PN->getIncomingBlock(i) != DestBlock) {
- ShouldDemote = true;
- break;
- }
- }
-
- if (ShouldDemote) {
- // We found a use outside of the tail. Create a new stack slot to
- // break this inter-block usage pattern.
- DemoteRegToStack(*I);
- break;
- }
+ if (I->isUsedOutsideOfBlock(DestBlock)) {
+ // We found a use outside of the tail. Create a new stack slot to
+ // break this inter-block usage pattern.
+ DemoteRegToStack(*I);
}
// We are going to have to map operands from the original block B to the new
// instructions one last time, constant propagating and DCE'ing them, because
// they may not be needed anymore.
//
- if (HadPHINodes)
- while (BI != SourceBlock->end())
- if (!dceInstruction(BI) && !doConstantPropagation(BI))
- ++BI;
+ if (HadPHINodes) {
+ while (BI != SourceBlock->end()) {
+ Instruction *Inst = BI++;
+ if (isInstructionTriviallyDead(Inst))
+ Inst->eraseFromParent();
+ else if (Constant *C = ConstantFoldInstruction(Inst)) {
+ Inst->replaceAllUsesWith(C);
+ Inst->eraseFromParent();
+ }
+ }
+ }
++NumEliminated; // We just killed a branch!
}
projects / oota-llvm.git / blobdiff