#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LazyValueInfo.h"
#include "llvm/Analysis/Loads.h"
-#include "llvm/DataLayout.h"
-#include "llvm/IntrinsicInst.h"
-#include "llvm/LLVMContext.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/LLVMContext.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
bool ProcessBranchOnXOR(BinaryOperator *BO);
bool SimplifyPartiallyRedundantLoad(LoadInst *LI);
+ bool TryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB);
};
}
// as having cost of 2 total, and if they are a vector intrinsic, we model
// them as having cost 1.
if (const CallInst *CI = dyn_cast<CallInst>(I)) {
- if (!isa<IntrinsicInst>(CI))
+ if (CI->hasFnAttr(Attribute::NoDuplicate))
+ // Blocks with NoDuplicate are modelled as having infinite cost, so they
+ // are never duplicated.
+ return ~0U;
+ else if (!isa<IntrinsicInst>(CI))
Size += 3;
else if (!CI->getType()->isVectorTy())
Size += 1;
return true;
}
}
+
}
+
+ if (CondBr && CondConst && TryToUnfoldSelect(CondCmp, BB))
+ return true;
}
// Check for some cases that are worth simplifying. Right now we want to look
return false;
}
-
/// SimplifyPartiallyRedundantLoad - If LI is an obviously partially redundant
/// load instruction, eliminate it by replacing it with a PHI node. This is an
/// important optimization that encourages jump threading, and needs to be run
if (LoadBB->getSinglePredecessor())
return false;
+ // If the load is defined in a landing pad, it can't be partially redundant,
+ // because the edges between the invoke and the landing pad cannot have other
+ // instructions between them.
+ if (LoadBB->isLandingPad())
+ return false;
+
Value *LoadedPtr = LI->getOperand(0);
// If the loaded operand is defined in the LoadBB, it can't be available.
return true;
}
+/// TryToUnfoldSelect - Look for blocks of the form
+/// bb1:
+/// %a = select
+/// br bb
+///
+/// bb2:
+/// %p = phi [%a, %bb] ...
+/// %c = icmp %p
+/// br i1 %c
+///
+/// And expand the select into a branch structure if one of its arms allows %c
+/// to be folded. This later enables threading from bb1 over bb2.
+bool JumpThreading::TryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB) {
+ BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
+ PHINode *CondLHS = dyn_cast<PHINode>(CondCmp->getOperand(0));
+ Constant *CondRHS = cast<Constant>(CondCmp->getOperand(1));
+
+ if (!CondBr || !CondBr->isConditional() || !CondLHS ||
+ CondLHS->getParent() != BB)
+ return false;
+
+ for (unsigned I = 0, E = CondLHS->getNumIncomingValues(); I != E; ++I) {
+ BasicBlock *Pred = CondLHS->getIncomingBlock(I);
+ SelectInst *SI = dyn_cast<SelectInst>(CondLHS->getIncomingValue(I));
+ // Look if one of the incoming values is a select in the corresponding
+ // predecessor.
+ if (!SI || SI->getParent() != Pred || !SI->hasOneUse())
+ continue;
+
+ BranchInst *PredTerm = dyn_cast<BranchInst>(Pred->getTerminator());
+ if (!PredTerm || !PredTerm->isUnconditional())
+ continue;
+
+ // Now check if one of the select values would allow us to constant fold the
+ // terminator in BB. We don't do the transform if both sides fold, those
+ // cases will be threaded in any case.
+ LazyValueInfo::Tristate LHSFolds =
+ LVI->getPredicateOnEdge(CondCmp->getPredicate(), SI->getOperand(1),
+ CondRHS, Pred, BB);
+ LazyValueInfo::Tristate RHSFolds =
+ LVI->getPredicateOnEdge(CondCmp->getPredicate(), SI->getOperand(2),
+ CondRHS, Pred, BB);
+ if ((LHSFolds != LazyValueInfo::Unknown ||
+ RHSFolds != LazyValueInfo::Unknown) &&
+ LHSFolds != RHSFolds) {
+ // Expand the select.
+ //
+ // Pred --
+ // | v
+ // | NewBB
+ // | |
+ // |-----
+ // v
+ // BB
+ BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "select.unfold",
+ BB->getParent(), BB);
+ // Move the unconditional branch to NewBB.
+ PredTerm->removeFromParent();
+ NewBB->getInstList().insert(NewBB->end(), PredTerm);
+ // Create a conditional branch and update PHI nodes.
+ BranchInst::Create(NewBB, BB, SI->getCondition(), Pred);
+ CondLHS->setIncomingValue(I, SI->getFalseValue());
+ CondLHS->addIncoming(SI->getTrueValue(), NewBB);
+ // The select is now dead.
+ SI->eraseFromParent();
+
+ // Update any other PHI nodes in BB.
+ for (BasicBlock::iterator BI = BB->begin();
+ PHINode *Phi = dyn_cast<PHINode>(BI); ++BI)
+ if (Phi != CondLHS)
+ Phi->addIncoming(Phi->getIncomingValueForBlock(Pred), NewBB);
+ return true;
+ }
+ }
+ return false;
+}