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-rw-r--r--lib/Transforms/Utils/SimplifyCFG.cpp143
1 files changed, 127 insertions, 16 deletions
diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 681bf9c..6d12f7a 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -59,6 +59,10 @@ static cl::opt<bool>
SinkCommon("simplifycfg-sink-common", cl::Hidden, cl::init(true),
cl::desc("Sink common instructions down to the end block"));
+static cl::opt<bool>
+HoistCondStores("simplifycfg-hoist-cond-stores", cl::Hidden, cl::init(true),
+ cl::desc("Hoist conditional stores if an unconditional store preceeds"));
+
STATISTIC(NumBitMaps, "Number of switch instructions turned into bitmaps");
STATISTIC(NumLookupTables, "Number of switch instructions turned into lookup tables");
STATISTIC(NumSinkCommons, "Number of common instructions sunk down to the end block");
@@ -277,7 +281,7 @@ static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
return BI->getCondition();
}
-/// ComputeSpeculuationCost - Compute an abstract "cost" of speculating the
+/// 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) {
@@ -529,9 +533,7 @@ Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
} else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
if (BI->isConditional() && BI->getCondition()->hasOneUse())
if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
- if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
- ICI->getPredicate() == ICmpInst::ICMP_NE) &&
- GetConstantInt(ICI->getOperand(1), TD))
+ if (ICI->isEquality() && GetConstantInt(ICI->getOperand(1), TD))
CV = ICI->getOperand(0);
// Unwrap any lossless ptrtoint cast.
@@ -1079,9 +1081,9 @@ static bool HoistThenElseCodeToIf(BranchInst *BI) {
(isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
return false;
- // If we get here, we can hoist at least one instruction.
BasicBlock *BIParent = BI->getParent();
+ bool Changed = false;
do {
// If we are hoisting the terminator instruction, don't move one (making a
// broken BB), instead clone it, and remove BI.
@@ -1096,6 +1098,7 @@ static bool HoistThenElseCodeToIf(BranchInst *BI) {
I2->replaceAllUsesWith(I1);
I1->intersectOptionalDataWith(I2);
I2->eraseFromParent();
+ Changed = true;
I1 = BB1_Itr++;
I2 = BB2_Itr++;
@@ -1115,7 +1118,23 @@ static bool HoistThenElseCodeToIf(BranchInst *BI) {
HoistTerminator:
// It may not be possible to hoist an invoke.
if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
- return true;
+ return Changed;
+
+ for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
+ PHINode *PN;
+ for (BasicBlock::iterator BBI = SI->begin();
+ (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
+ Value *BB1V = PN->getIncomingValueForBlock(BB1);
+ Value *BB2V = PN->getIncomingValueForBlock(BB2);
+ if (BB1V == BB2V)
+ continue;
+
+ if (isa<ConstantExpr>(BB1V) && !isSafeToSpeculativelyExecute(BB1V))
+ return Changed;
+ if (isa<ConstantExpr>(BB2V) && !isSafeToSpeculativelyExecute(BB2V))
+ return Changed;
+ }
+ }
// Okay, it is safe to hoist the terminator.
Instruction *NT = I1->clone();
@@ -1332,6 +1351,66 @@ static bool SinkThenElseCodeToEnd(BranchInst *BI1) {
return Changed;
}
+/// \brief Determine if we can hoist sink a sole store instruction out of a
+/// conditional block.
+///
+/// We are looking for code like the following:
+/// BrBB:
+/// store i32 %add, i32* %arrayidx2
+/// ... // No other stores or function calls (we could be calling a memory
+/// ... // function).
+/// %cmp = icmp ult %x, %y
+/// br i1 %cmp, label %EndBB, label %ThenBB
+/// ThenBB:
+/// store i32 %add5, i32* %arrayidx2
+/// br label EndBB
+/// EndBB:
+/// ...
+/// We are going to transform this into:
+/// BrBB:
+/// store i32 %add, i32* %arrayidx2
+/// ... //
+/// %cmp = icmp ult %x, %y
+/// %add.add5 = select i1 %cmp, i32 %add, %add5
+/// store i32 %add.add5, i32* %arrayidx2
+/// ...
+///
+/// \return The pointer to the value of the previous store if the store can be
+/// hoisted into the predecessor block. 0 otherwise.
+static Value *isSafeToSpeculateStore(Instruction *I, BasicBlock *BrBB,
+ BasicBlock *StoreBB, BasicBlock *EndBB) {
+ StoreInst *StoreToHoist = dyn_cast<StoreInst>(I);
+ if (!StoreToHoist)
+ return 0;
+
+ // Volatile or atomic.
+ if (!StoreToHoist->isSimple())
+ return 0;
+
+ Value *StorePtr = StoreToHoist->getPointerOperand();
+
+ // Look for a store to the same pointer in BrBB.
+ unsigned MaxNumInstToLookAt = 10;
+ for (BasicBlock::reverse_iterator RI = BrBB->rbegin(),
+ RE = BrBB->rend(); RI != RE && (--MaxNumInstToLookAt); ++RI) {
+ Instruction *CurI = &*RI;
+
+ // Could be calling an instruction that effects memory like free().
+ if (CurI->mayHaveSideEffects() && !isa<StoreInst>(CurI))
+ return 0;
+
+ StoreInst *SI = dyn_cast<StoreInst>(CurI);
+ // Found the previous store make sure it stores to the same location.
+ if (SI && SI->getPointerOperand() == StorePtr)
+ // Found the previous store, return its value operand.
+ return SI->getValueOperand();
+ else if (SI)
+ return 0; // Unknown store.
+ }
+
+ return 0;
+}
+
/// \brief Speculate a conditional basic block flattening the CFG.
///
/// Note that this is a very risky transform currently. Speculating
@@ -1395,6 +1474,8 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB) {
SmallDenseMap<Instruction *, unsigned, 4> SinkCandidateUseCounts;
unsigned SpeculationCost = 0;
+ Value *SpeculatedStoreValue = 0;
+ StoreInst *SpeculatedStore = 0;
for (BasicBlock::iterator BBI = ThenBB->begin(),
BBE = llvm::prior(ThenBB->end());
BBI != BBE; ++BBI) {
@@ -1410,13 +1491,21 @@ 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) &&
+ !(HoistCondStores &&
+ (SpeculatedStoreValue = isSafeToSpeculateStore(I, BB, ThenBB,
+ EndBB))))
return false;
- if (ComputeSpeculationCost(I) > PHINodeFoldingThreshold)
+ if (!SpeculatedStoreValue &&
+ ComputeSpeculationCost(I) > PHINodeFoldingThreshold)
return false;
+ // Store the store speculation candidate.
+ if (SpeculatedStoreValue)
+ SpeculatedStore = cast<StoreInst>(I);
+
// Do not hoist the instruction if any of its operands are defined but not
- // used in this BB. The transformation will prevent the operand from
+ // used in BB. The transformation will prevent the operand from
// being sunk into the use block.
for (User::op_iterator i = I->op_begin(), e = I->op_end();
i != e; ++i) {
@@ -1448,18 +1537,23 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB) {
Value *OrigV = PN->getIncomingValueForBlock(BB);
Value *ThenV = PN->getIncomingValueForBlock(ThenBB);
+ // FIXME: Try to remove some of the duplication with HoistThenElseCodeToIf.
// Skip PHIs which are trivial.
if (ThenV == OrigV)
continue;
HaveRewritablePHIs = true;
- ConstantExpr *CE = dyn_cast<ConstantExpr>(ThenV);
- if (!CE)
+ ConstantExpr *OrigCE = dyn_cast<ConstantExpr>(OrigV);
+ ConstantExpr *ThenCE = dyn_cast<ConstantExpr>(ThenV);
+ if (!OrigCE && !ThenCE)
continue; // Known safe and cheap.
- if (!isSafeToSpeculativelyExecute(CE))
+ if ((ThenCE && !isSafeToSpeculativelyExecute(ThenCE)) ||
+ (OrigCE && !isSafeToSpeculativelyExecute(OrigCE)))
return false;
- if (ComputeSpeculationCost(CE) > PHINodeFoldingThreshold)
+ unsigned OrigCost = OrigCE ? ComputeSpeculationCost(OrigCE) : 0;
+ unsigned ThenCost = ThenCE ? ComputeSpeculationCost(ThenCE) : 0;
+ if (OrigCost + ThenCost > 2 * PHINodeFoldingThreshold)
return false;
// Account for the cost of an unfolded ConstantExpr which could end up
@@ -1473,12 +1567,24 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB) {
// If there are no PHIs to process, bail early. This helps ensure idempotence
// as well.
- if (!HaveRewritablePHIs)
+ if (!HaveRewritablePHIs && !(HoistCondStores && SpeculatedStoreValue))
return false;
// If we get here, we can hoist the instruction and if-convert.
DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *ThenBB << "\n";);
+ // Insert a select of the value of the speculated store.
+ if (SpeculatedStoreValue) {
+ IRBuilder<true, NoFolder> Builder(BI);
+ Value *TrueV = SpeculatedStore->getValueOperand();
+ Value *FalseV = SpeculatedStoreValue;
+ if (Invert)
+ std::swap(TrueV, FalseV);
+ Value *S = Builder.CreateSelect(BrCond, TrueV, FalseV, TrueV->getName() +
+ "." + FalseV->getName());
+ SpeculatedStore->setOperand(0, S);
+ }
+
// Hoist the instructions.
BB->getInstList().splice(BI, ThenBB->getInstList(), ThenBB->begin(),
llvm::prior(ThenBB->end()));
@@ -3073,7 +3179,12 @@ static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
Value *Sub = SI->getCondition();
if (!Offset->isNullValue())
Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off");
- Value *Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
+ Value *Cmp;
+ // If NumCases overflowed, then all possible values jump to the successor.
+ if (NumCases->isNullValue() && SI->getNumCases() != 0)
+ Cmp = ConstantInt::getTrue(SI->getContext());
+ else
+ Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
BranchInst *NewBI = Builder.CreateCondBr(
Cmp, SI->case_begin().getCaseSuccessor(), SI->getDefaultDest());
@@ -3552,7 +3663,7 @@ bool SwitchLookupTable::WouldFitInRegister(const DataLayout *TD,
}
/// ShouldBuildLookupTable - Determine whether a lookup table should be built
-/// for this switch, based on the number of caes, size of the table and the
+/// for this switch, based on the number of cases, size of the table and the
/// types of the results.
static bool ShouldBuildLookupTable(SwitchInst *SI,
uint64_t TableSize,