//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "correlated-value-propagation"
#include "llvm/Transforms/Scalar.h"
-#include "llvm/Constants.h"
-#include "llvm/Function.h"
-#include "llvm/Instructions.h"
-#include "llvm/Pass.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LazyValueInfo.h"
-#include "llvm/Support/CFG.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/Local.h"
-#include "llvm/ADT/Statistic.h"
using namespace llvm;
+#define DEBUG_TYPE "correlated-value-propagation"
+
STATISTIC(NumPhis, "Number of phis propagated");
STATISTIC(NumSelects, "Number of selects propagated");
STATISTIC(NumMemAccess, "Number of memory access targets propagated");
STATISTIC(NumCmps, "Number of comparisons propagated");
+STATISTIC(NumReturns, "Number of return values propagated");
+STATISTIC(NumDeadCases, "Number of switch cases removed");
namespace {
class CorrelatedValuePropagation : public FunctionPass {
bool processMemAccess(Instruction *I);
bool processCmp(CmpInst *C);
bool processSwitch(SwitchInst *SI);
+ bool processCallSite(CallSite CS);
+
+ /// Return a constant value for V usable at At and everything it
+ /// dominates. If no such Constant can be found, return nullptr.
+ Constant *getConstantAt(Value *V, Instruction *At);
public:
static char ID;
initializeCorrelatedValuePropagationPass(*PassRegistry::getPassRegistry());
}
- bool runOnFunction(Function &F);
+ bool runOnFunction(Function &F) override;
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<LazyValueInfo>();
+ AU.addPreserved<GlobalsAAWrapperPass>();
}
};
}
if (S->getType()->isVectorTy()) return false;
if (isa<Constant>(S->getOperand(0))) return false;
- Constant *C = LVI->getConstant(S->getOperand(0), S->getParent());
+ Constant *C = LVI->getConstant(S->getOperand(0), S->getParent(), S);
if (!C) return false;
ConstantInt *CI = dyn_cast<ConstantInt>(C);
Value *Incoming = P->getIncomingValue(i);
if (isa<Constant>(Incoming)) continue;
- Constant *C = LVI->getConstantOnEdge(P->getIncomingValue(i),
- P->getIncomingBlock(i),
- BB);
- if (!C) continue;
+ Value *V = LVI->getConstantOnEdge(Incoming, P->getIncomingBlock(i), BB, P);
+
+ // Look if the incoming value is a select with a scalar condition for which
+ // LVI can tells us the value. In that case replace the incoming value with
+ // the appropriate value of the select. This often allows us to remove the
+ // select later.
+ if (!V) {
+ SelectInst *SI = dyn_cast<SelectInst>(Incoming);
+ if (!SI) continue;
+
+ Value *Condition = SI->getCondition();
+ if (!Condition->getType()->isVectorTy()) {
+ if (Constant *C = LVI->getConstantOnEdge(
+ Condition, P->getIncomingBlock(i), BB, P)) {
+ if (C->isOneValue()) {
+ V = SI->getTrueValue();
+ } else if (C->isZeroValue()) {
+ V = SI->getFalseValue();
+ }
+ // Once LVI learns to handle vector types, we could also add support
+ // for vector type constants that are not all zeroes or all ones.
+ }
+ }
+
+ // Look if the select has a constant but LVI tells us that the incoming
+ // value can never be that constant. In that case replace the incoming
+ // value with the other value of the select. This often allows us to
+ // remove the select later.
+ if (!V) {
+ Constant *C = dyn_cast<Constant>(SI->getFalseValue());
+ if (!C) continue;
+
+ if (LVI->getPredicateOnEdge(ICmpInst::ICMP_EQ, SI, C,
+ P->getIncomingBlock(i), BB, P) !=
+ LazyValueInfo::False)
+ continue;
+ V = SI->getTrueValue();
+ }
- P->setIncomingValue(i, C);
+ DEBUG(dbgs() << "CVP: Threading PHI over " << *SI << '\n');
+ }
+
+ P->setIncomingValue(i, V);
Changed = true;
}
- if (Value *V = SimplifyInstruction(P)) {
+ // FIXME: Provide TLI, DT, AT to SimplifyInstruction.
+ const DataLayout &DL = BB->getModule()->getDataLayout();
+ if (Value *V = SimplifyInstruction(P, DL)) {
P->replaceAllUsesWith(V);
P->eraseFromParent();
Changed = true;
}
- ++NumPhis;
+ if (Changed)
+ ++NumPhis;
return Changed;
}
bool CorrelatedValuePropagation::processMemAccess(Instruction *I) {
- Value *Pointer = 0;
+ Value *Pointer = nullptr;
if (LoadInst *L = dyn_cast<LoadInst>(I))
Pointer = L->getPointerOperand();
else
if (isa<Constant>(Pointer)) return false;
- Constant *C = LVI->getConstant(Pointer, I->getParent());
+ Constant *C = LVI->getConstant(Pointer, I->getParent(), I);
if (!C) return false;
++NumMemAccess;
return true;
}
-/// processCmp - If the value of this comparison could be determined locally,
-/// constant propagation would already have figured it out. Instead, walk
-/// the predecessors and statically evaluate the comparison based on information
-/// available on that edge. If a given static evaluation is true on ALL
-/// incoming edges, then it's true universally and we can simplify the compare.
+/// processCmp - See if LazyValueInfo's ability to exploit edge conditions,
+/// or range information is sufficient to prove this comparison. Even for
+/// local conditions, this can sometimes prove conditions instcombine can't by
+/// exploiting range information.
bool CorrelatedValuePropagation::processCmp(CmpInst *C) {
Value *Op0 = C->getOperand(0);
- if (isa<Instruction>(Op0) &&
- cast<Instruction>(Op0)->getParent() == C->getParent())
- return false;
-
Constant *Op1 = dyn_cast<Constant>(C->getOperand(1));
if (!Op1) return false;
- pred_iterator PI = pred_begin(C->getParent()), PE = pred_end(C->getParent());
- if (PI == PE) return false;
+ // As a policy choice, we choose not to waste compile time on anything where
+ // the comparison is testing local values. While LVI can sometimes reason
+ // about such cases, it's not its primary purpose. We do make sure to do
+ // the block local query for uses from terminator instructions, but that's
+ // handled in the code for each terminator.
+ auto *I = dyn_cast<Instruction>(Op0);
+ if (I && I->getParent() == C->getParent())
+ return false;
- LazyValueInfo::Tristate Result = LVI->getPredicateOnEdge(C->getPredicate(),
- C->getOperand(0), Op1, *PI, C->getParent());
+ LazyValueInfo::Tristate Result =
+ LVI->getPredicateAt(C->getPredicate(), Op0, Op1, C);
if (Result == LazyValueInfo::Unknown) return false;
- ++PI;
- while (PI != PE) {
- LazyValueInfo::Tristate Res = LVI->getPredicateOnEdge(C->getPredicate(),
- C->getOperand(0), Op1, *PI, C->getParent());
- if (Res != Result) return false;
- ++PI;
- }
-
++NumCmps;
-
if (Result == LazyValueInfo::True)
C->replaceAllUsesWith(ConstantInt::getTrue(C->getContext()));
else
C->replaceAllUsesWith(ConstantInt::getFalse(C->getContext()));
-
C->eraseFromParent();
return true;
// Analyse each switch case in turn. This is done in reverse order so that
// removing a case doesn't cause trouble for the iteration.
bool Changed = false;
- for (SwitchInst::CaseIt CI = SI->caseEnd(), CE = SI->caseBegin(); CI-- != CE;
+ for (SwitchInst::CaseIt CI = SI->case_end(), CE = SI->case_begin(); CI-- != CE;
) {
ConstantInt *Case = CI.getCaseValue();
for (pred_iterator PI = PB; PI != PE; ++PI) {
// Is the switch condition equal to the case value?
LazyValueInfo::Tristate Value = LVI->getPredicateOnEdge(CmpInst::ICMP_EQ,
- Cond, Case, *PI, BB);
+ Cond, Case, *PI,
+ BB, SI);
// Give up on this case if nothing is known.
if (Value == LazyValueInfo::Unknown) {
State = LazyValueInfo::Unknown;
// This case never fires - remove it.
CI.getCaseSuccessor()->removePredecessor(BB);
SI->removeCase(CI); // Does not invalidate the iterator.
+
+ // The condition can be modified by removePredecessor's PHI simplification
+ // logic.
+ Cond = SI->getCondition();
+
+ ++NumDeadCases;
Changed = true;
} else if (State == LazyValueInfo::True) {
// This case always fires. Arrange for the switch to be turned into an
// unconditional branch by replacing the switch condition with the case
// value.
SI->setCondition(Case);
+ NumDeadCases += SI->getNumCases();
Changed = true;
break;
}
return Changed;
}
+/// processCallSite - Infer nonnull attributes for the arguments at the
+/// specified callsite.
+bool CorrelatedValuePropagation::processCallSite(CallSite CS) {
+ bool Changed = false;
+
+ unsigned ArgNo = 0;
+ for (Value *V : CS.args()) {
+ PointerType *Type = dyn_cast<PointerType>(V->getType());
+
+ if (Type && !CS.paramHasAttr(ArgNo + 1, Attribute::NonNull) &&
+ LVI->getPredicateAt(ICmpInst::ICMP_EQ, V,
+ ConstantPointerNull::get(Type),
+ CS.getInstruction()) == LazyValueInfo::False) {
+ AttributeSet AS = CS.getAttributes();
+ AS = AS.addAttribute(CS.getInstruction()->getContext(), ArgNo + 1,
+ Attribute::NonNull);
+ CS.setAttributes(AS);
+ Changed = true;
+ }
+ ArgNo++;
+ }
+ assert(ArgNo == CS.arg_size() && "sanity check");
+
+ return Changed;
+}
+
+Constant *CorrelatedValuePropagation::getConstantAt(Value *V, Instruction *At) {
+ if (Constant *C = LVI->getConstant(V, At->getParent(), At))
+ return C;
+
+ // TODO: The following really should be sunk inside LVI's core algorithm, or
+ // at least the outer shims around such.
+ auto *C = dyn_cast<CmpInst>(V);
+ if (!C) return nullptr;
+
+ Value *Op0 = C->getOperand(0);
+ Constant *Op1 = dyn_cast<Constant>(C->getOperand(1));
+ if (!Op1) return nullptr;
+
+ LazyValueInfo::Tristate Result =
+ LVI->getPredicateAt(C->getPredicate(), Op0, Op1, At);
+ if (Result == LazyValueInfo::Unknown)
+ return nullptr;
+
+ return (Result == LazyValueInfo::True) ?
+ ConstantInt::getTrue(C->getContext()) :
+ ConstantInt::getFalse(C->getContext());
+}
+
bool CorrelatedValuePropagation::runOnFunction(Function &F) {
+ if (skipOptnoneFunction(F))
+ return false;
+
LVI = &getAnalysis<LazyValueInfo>();
bool FnChanged = false;
for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
bool BBChanged = false;
for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ) {
- Instruction *II = BI++;
+ Instruction *II = &*BI++;
switch (II->getOpcode()) {
case Instruction::Select:
BBChanged |= processSelect(cast<SelectInst>(II));
case Instruction::Store:
BBChanged |= processMemAccess(II);
break;
+ case Instruction::Call:
+ case Instruction::Invoke:
+ BBChanged |= processCallSite(CallSite(II));
+ break;
}
}
case Instruction::Switch:
BBChanged |= processSwitch(cast<SwitchInst>(Term));
break;
+ case Instruction::Ret: {
+ auto *RI = cast<ReturnInst>(Term);
+ // Try to determine the return value if we can. This is mainly here to
+ // simplify the writing of unit tests, but also helps to enable IPO by
+ // constant folding the return values of callees.
+ auto *RetVal = RI->getReturnValue();
+ if (!RetVal) break; // handle "ret void"
+ if (isa<Constant>(RetVal)) break; // nothing to do
+ if (auto *C = getConstantAt(RetVal, RI)) {
+ ++NumReturns;
+ RI->replaceUsesOfWith(RetVal, C);
+ BBChanged = true;
+ }
}
+ };
FnChanged |= BBChanged;
}
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