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Feeding isSafeToSpeculativelyExecute its DataLayout pointer

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isSafeToSpeculativelyExecute can optionally take a DataLayout pointer. In the
past, this was mainly used to make better decisions regarding divisions known
not to trap, and so was not all that important for users concerned with "cheap"
instructions. However, now it also helps look through bitcasts for
dereferencable loads, and will also be important if/when we add a
dereferencable pointer attribute.

This is some initial work to feed a DataLayout pointer through to callers of
isSafeToSpeculativelyExecute, generally where one was already available.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212720 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hal Finkel
2014-07-10 14:41:31 +00:00
parent 6b0ac2aa02
commit 73118c4128
7 changed files with 52 additions and 36 deletions
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52
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -201,8 +201,8 @@ static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
/// ComputeSpeculationCost - Compute an abstract "cost" of speculating the
/// given instruction, which is assumed to be safe to speculate. 1 means
/// cheap, 2 means less cheap, and UINT_MAX means prohibitively expensive.
static unsigned ComputeSpeculationCost(const User *I) {
assert(isSafeToSpeculativelyExecute(I) &&
static unsigned ComputeSpeculationCost(const User *I, const DataLayout *DL) {
assert(isSafeToSpeculativelyExecute(I, DL) &&
"Instruction is not safe to speculatively execute!");
switch (Operator::getOpcode(I)) {
default:
@ -257,7 +257,8 @@ static unsigned ComputeSpeculationCost(const User *I) {
/// CostRemaining, false is returned and CostRemaining is undefined.
static bool DominatesMergePoint(Value *V, BasicBlock *BB,
SmallPtrSet<Instruction*, 4> *AggressiveInsts,
unsigned &CostRemaining) {
unsigned &CostRemaining,
const DataLayout *DL) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I) {
// Non-instructions all dominate instructions, but not all constantexprs
@ -290,10 +291,10 @@ static bool DominatesMergePoint(Value *V, BasicBlock *BB,
// Okay, it looks like the instruction IS in the "condition". Check to
// see if it's a cheap instruction to unconditionally compute, and if it
// only uses stuff defined outside of the condition. If so, hoist it out.
if (!isSafeToSpeculativelyExecute(I))
if (!isSafeToSpeculativelyExecute(I, DL))
return false;
unsigned Cost = ComputeSpeculationCost(I);
unsigned Cost = ComputeSpeculationCost(I, DL);
if (Cost > CostRemaining)
return false;
@ -303,7 +304,7 @@ static bool DominatesMergePoint(Value *V, BasicBlock *BB,
// Okay, we can only really hoist these out if their operands do
// not take us over the cost threshold.
for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining))
if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining, DL))
return false;
// Okay, it's safe to do this! Remember this instruction.
AggressiveInsts->insert(I);
@ -997,7 +998,7 @@ static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
/// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
/// BB2, hoist any common code in the two blocks up into the branch block. The
/// caller of this function guarantees that BI's block dominates BB1 and BB2.
static bool HoistThenElseCodeToIf(BranchInst *BI) {
static bool HoistThenElseCodeToIf(BranchInst *BI, const DataLayout *DL) {
// This does very trivial matching, with limited scanning, to find identical
// instructions in the two blocks. In particular, we don't want to get into
// O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
@ -1071,9 +1072,9 @@ HoistTerminator:
if (BB1V == BB2V)
continue;
if (isa<ConstantExpr>(BB1V) && !isSafeToSpeculativelyExecute(BB1V))
if (isa<ConstantExpr>(BB1V) && !isSafeToSpeculativelyExecute(BB1V, DL))
return Changed;
if (isa<ConstantExpr>(BB2V) && !isSafeToSpeculativelyExecute(BB2V))
if (isa<ConstantExpr>(BB2V) && !isSafeToSpeculativelyExecute(BB2V, DL))
return Changed;
}
}
@ -1390,7 +1391,8 @@ static Value *isSafeToSpeculateStore(Instruction *I, BasicBlock *BrBB,
/// \endcode
///
/// \returns true if the conditional block is removed.
static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB) {
static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
const DataLayout *DL) {
// Be conservative for now. FP select instruction can often be expensive.
Value *BrCond = BI->getCondition();
if (isa<FCmpInst>(BrCond))
@ -1433,13 +1435,13 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB) {
return false;
// Don't hoist the instruction if it's unsafe or expensive.
if (!isSafeToSpeculativelyExecute(I) &&
if (!isSafeToSpeculativelyExecute(I, DL) &&
!(HoistCondStores &&
(SpeculatedStoreValue = isSafeToSpeculateStore(I, BB, ThenBB,
EndBB))))
return false;
if (!SpeculatedStoreValue &&
ComputeSpeculationCost(I) > PHINodeFoldingThreshold)
ComputeSpeculationCost(I, DL) > PHINodeFoldingThreshold)
return false;
// Store the store speculation candidate.
@ -1490,11 +1492,11 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB) {
if (!OrigCE && !ThenCE)
continue; // Known safe and cheap.
if ((ThenCE && !isSafeToSpeculativelyExecute(ThenCE)) ||
(OrigCE && !isSafeToSpeculativelyExecute(OrigCE)))
if ((ThenCE && !isSafeToSpeculativelyExecute(ThenCE, DL)) ||
(OrigCE && !isSafeToSpeculativelyExecute(OrigCE, DL)))
return false;
unsigned OrigCost = OrigCE ? ComputeSpeculationCost(OrigCE) : 0;
unsigned ThenCost = ThenCE ? ComputeSpeculationCost(ThenCE) : 0;
unsigned OrigCost = OrigCE ? ComputeSpeculationCost(OrigCE, DL) : 0;
unsigned ThenCost = ThenCE ? ComputeSpeculationCost(ThenCE, DL) : 0;
if (OrigCost + ThenCost > 2 * PHINodeFoldingThreshold)
return false;
@ -1741,9 +1743,9 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const DataLayout *DL) {
}
if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
MaxCostVal0) ||
MaxCostVal0, DL) ||
!DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
MaxCostVal1))
MaxCostVal1, DL))
return false;
}
@ -1961,7 +1963,7 @@ static bool checkCSEInPredecessor(Instruction *Inst, BasicBlock *PB) {
/// FoldBranchToCommonDest - If this basic block is simple enough, and if a
/// predecessor branches to us and one of our successors, fold the block into
/// the predecessor and use logical operations to pick the right destination.
bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
bool llvm::FoldBranchToCommonDest(BranchInst *BI, const DataLayout *DL) {
BasicBlock *BB = BI->getParent();
Instruction *Cond = nullptr;
@ -2013,7 +2015,7 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
Instruction *BonusInst = nullptr;
if (&*FrontIt != Cond &&
FrontIt->hasOneUse() && FrontIt->user_back() == Cond &&
isSafeToSpeculativelyExecute(FrontIt)) {
isSafeToSpeculativelyExecute(FrontIt, DL)) {
BonusInst = &*FrontIt;
++FrontIt;
@ -4016,7 +4018,7 @@ bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){
// branches to us and our successor, fold the comparison into the
// predecessor and use logical operations to update the incoming value
// for PHI nodes in common successor.
if (FoldBranchToCommonDest(BI))
if (FoldBranchToCommonDest(BI, DL))
return SimplifyCFG(BB, TTI, DL) | true;
return false;
}
@ -4060,7 +4062,7 @@ bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
// If this basic block is ONLY a compare and a branch, and if a predecessor
// branches to us and one of our successors, fold the comparison into the
// predecessor and use logical operations to pick the right destination.
if (FoldBranchToCommonDest(BI))
if (FoldBranchToCommonDest(BI, DL))
return SimplifyCFG(BB, TTI, DL) | true;
// We have a conditional branch to two blocks that are only reachable
@ -4069,7 +4071,7 @@ bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
// can hoist it up to the branching block.
if (BI->getSuccessor(0)->getSinglePredecessor()) {
if (BI->getSuccessor(1)->getSinglePredecessor()) {
if (HoistThenElseCodeToIf(BI))
if (HoistThenElseCodeToIf(BI, DL))
return SimplifyCFG(BB, TTI, DL) | true;
} else {
// If Successor #1 has multiple preds, we may be able to conditionally
@ -4077,7 +4079,7 @@ bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
if (Succ0TI->getNumSuccessors() == 1 &&
Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0), DL))
return SimplifyCFG(BB, TTI, DL) | true;
}
} else if (BI->getSuccessor(1)->getSinglePredecessor()) {
@ -4086,7 +4088,7 @@ bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
if (Succ1TI->getNumSuccessors() == 1 &&
Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1), DL))
return SimplifyCFG(BB, TTI, DL) | true;
}