//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "correlated-value-propagation"
#include "llvm/Transforms/Scalar.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/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;
-STATISTIC(NumPhis, "Number of phis propagated");
-STATISTIC(NumSelects, "Number of selects propagated");
+#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 {
LazyValueInfo *LVI;
-
+
bool processSelect(SelectInst *SI);
bool processPHI(PHINode *P);
-
+ 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;
- CorrelatedValuePropagation(): FunctionPass(ID) { }
-
- bool runOnFunction(Function &F);
-
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ CorrelatedValuePropagation(): FunctionPass(ID) {
+ initializeCorrelatedValuePropagationPass(*PassRegistry::getPassRegistry());
+ }
+
+ bool runOnFunction(Function &F) override;
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<LazyValueInfo>();
+ AU.addPreserved<GlobalsAAWrapperPass>();
}
};
}
char CorrelatedValuePropagation::ID = 0;
-INITIALIZE_PASS(CorrelatedValuePropagation, "correlated-propagation",
- "Value Propagation", false, false);
+INITIALIZE_PASS_BEGIN(CorrelatedValuePropagation, "correlated-propagation",
+ "Value Propagation", false, false)
+INITIALIZE_PASS_DEPENDENCY(LazyValueInfo)
+INITIALIZE_PASS_END(CorrelatedValuePropagation, "correlated-propagation",
+ "Value Propagation", false, false)
// Public interface to the Value Propagation pass
Pass *llvm::createCorrelatedValuePropagationPass() {
bool CorrelatedValuePropagation::processSelect(SelectInst *S) {
if (S->getType()->isVectorTy()) return false;
-
- Constant *C = LVI->getConstant(S->getOperand(0), S->getParent());
+ if (isa<Constant>(S->getOperand(0))) return false;
+
+ Constant *C = LVI->getConstant(S->getOperand(0), S->getParent(), S);
if (!C) return false;
-
+
ConstantInt *CI = dyn_cast<ConstantInt>(C);
if (!CI) return false;
-
- S->replaceAllUsesWith(S->getOperand(CI->isOne() ? 1 : 2));
+
+ Value *ReplaceWith = S->getOperand(1);
+ Value *Other = S->getOperand(2);
+ if (!CI->isOne()) std::swap(ReplaceWith, Other);
+ if (ReplaceWith == S) ReplaceWith = UndefValue::get(S->getType());
+
+ S->replaceAllUsesWith(ReplaceWith);
S->eraseFromParent();
++NumSelects;
-
+
return true;
}
bool CorrelatedValuePropagation::processPHI(PHINode *P) {
bool Changed = false;
-
+
BasicBlock *BB = P->getParent();
for (unsigned i = 0, e = P->getNumIncomingValues(); i < e; ++i) {
Value *Incoming = P->getIncomingValue(i);
if (isa<Constant>(Incoming)) continue;
-
- Constant *C = LVI->getConstantOnEdge(P->getIncomingValue(i),
- P->getIncomingBlock(i),
- BB);
- if (!C) continue;
-
- P->setIncomingValue(i, C);
+
+ 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();
+ }
+
+ DEBUG(dbgs() << "CVP: Threading PHI over " << *SI << '\n');
+ }
+
+ P->setIncomingValue(i, V);
Changed = true;
}
-
- if (Value *ConstVal = P->hasConstantValue()) {
- P->replaceAllUsesWith(ConstVal);
+
+ // 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;
}
+
+ if (Changed)
+ ++NumPhis;
+
+ return Changed;
+}
+
+bool CorrelatedValuePropagation::processMemAccess(Instruction *I) {
+ Value *Pointer = nullptr;
+ if (LoadInst *L = dyn_cast<LoadInst>(I))
+ Pointer = L->getPointerOperand();
+ else
+ Pointer = cast<StoreInst>(I)->getPointerOperand();
+
+ if (isa<Constant>(Pointer)) return false;
+
+ Constant *C = LVI->getConstant(Pointer, I->getParent(), I);
+ if (!C) return false;
+
+ ++NumMemAccess;
+ I->replaceUsesOfWith(Pointer, C);
+ return true;
+}
+
+/// 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);
+ Constant *Op1 = dyn_cast<Constant>(C->getOperand(1));
+ if (!Op1) 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->getPredicateAt(C->getPredicate(), Op0, Op1, C);
+ if (Result == LazyValueInfo::Unknown) return false;
+
+ ++NumCmps;
+ if (Result == LazyValueInfo::True)
+ C->replaceAllUsesWith(ConstantInt::getTrue(C->getContext()));
+ else
+ C->replaceAllUsesWith(ConstantInt::getFalse(C->getContext()));
+ C->eraseFromParent();
+
+ return true;
+}
+
+/// processSwitch - Simplify a switch instruction by removing cases which can
+/// never fire. If the uselessness of a case could be determined locally then
+/// constant propagation would already have figured it out. Instead, walk the
+/// predecessors and statically evaluate cases based on information available
+/// on that edge. Cases that cannot fire no matter what the incoming edge can
+/// safely be removed. If a case fires on every incoming edge then the entire
+/// switch can be removed and replaced with a branch to the case destination.
+bool CorrelatedValuePropagation::processSwitch(SwitchInst *SI) {
+ Value *Cond = SI->getCondition();
+ BasicBlock *BB = SI->getParent();
+
+ // If the condition was defined in same block as the switch then LazyValueInfo
+ // currently won't say anything useful about it, though in theory it could.
+ if (isa<Instruction>(Cond) && cast<Instruction>(Cond)->getParent() == BB)
+ return false;
+
+ // If the switch is unreachable then trying to improve it is a waste of time.
+ pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
+ if (PB == PE) return false;
+
+ // 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->case_end(), CE = SI->case_begin(); CI-- != CE;
+ ) {
+ ConstantInt *Case = CI.getCaseValue();
+
+ // Check to see if the switch condition is equal to/not equal to the case
+ // value on every incoming edge, equal/not equal being the same each time.
+ LazyValueInfo::Tristate State = LazyValueInfo::Unknown;
+ 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, SI);
+ // Give up on this case if nothing is known.
+ if (Value == LazyValueInfo::Unknown) {
+ State = LazyValueInfo::Unknown;
+ break;
+ }
+
+ // If this was the first edge to be visited, record that all other edges
+ // need to give the same result.
+ if (PI == PB) {
+ State = Value;
+ continue;
+ }
+
+ // If this case is known to fire for some edges and known not to fire for
+ // others then there is nothing we can do - give up.
+ if (Value != State) {
+ State = LazyValueInfo::Unknown;
+ break;
+ }
+ }
+
+ if (State == LazyValueInfo::False) {
+ // 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;
+ }
+ }
+
+ if (Changed)
+ // If the switch has been simplified to the point where it can be replaced
+ // by a branch then do so now.
+ ConstantFoldTerminator(BB);
+
+ 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;
- ++NumPhis;
+ LazyValueInfo::Tristate Result =
+ LVI->getPredicateAt(C->getPredicate(), Op0, Op1, At);
+ if (Result == LazyValueInfo::Unknown)
+ return nullptr;
- return Changed;
+ 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 Changed = false;
-
- for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
+
+ 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++;
- if (SelectInst *SI = dyn_cast<SelectInst>(II))
- Changed |= processSelect(SI);
- else if (PHINode *P = dyn_cast<PHINode>(II))
- Changed |= processPHI(P);
+ Instruction *II = &*BI++;
+ switch (II->getOpcode()) {
+ case Instruction::Select:
+ BBChanged |= processSelect(cast<SelectInst>(II));
+ break;
+ case Instruction::PHI:
+ BBChanged |= processPHI(cast<PHINode>(II));
+ break;
+ case Instruction::ICmp:
+ case Instruction::FCmp:
+ BBChanged |= processCmp(cast<CmpInst>(II));
+ break;
+ case Instruction::Load:
+ case Instruction::Store:
+ BBChanged |= processMemAccess(II);
+ break;
+ case Instruction::Call:
+ case Instruction::Invoke:
+ BBChanged |= processCallSite(CallSite(II));
+ break;
+ }
}
-
- if (Changed)
- for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
- SimplifyInstructionsInBlock(FI);
-
- return Changed;
+
+ Instruction *Term = FI->getTerminator();
+ switch (Term->getOpcode()) {
+ 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;
+ }
+
+ return FnChanged;
}