//
//===----------------------------------------------------------------------===//
-#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/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/Pass.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/Local.h"
-#include "llvm/ADT/DepthFirstIterator.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(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);
+
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>();
}
};
bool CorrelatedValuePropagation::processSelect(SelectInst *S) {
if (S->getType()->isVectorTy()) return false;
if (isa<Constant>(S->getOperand(0))) return false;
-
+
Constant *C = LVI->getConstant(S->getOperand(0), S->getParent());
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);
+
+ // Look if the incoming value is a select with 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) {
+ SelectInst *SI = dyn_cast<SelectInst>(Incoming);
+ if (!SI) continue;
+
+ Constant *C = dyn_cast<Constant>(SI->getFalseValue());
+ if (!C) continue;
+
+ if (LVI->getPredicateOnEdge(ICmpInst::ICMP_EQ, SI, C,
+ P->getIncomingBlock(i), BB) !=
+ LazyValueInfo::False)
+ continue;
+
+ DEBUG(dbgs() << "CVP: Threading PHI over " << *SI << '\n');
+ V = SI->getTrueValue();
+ }
+
+ P->setIncomingValue(i, V);
Changed = true;
}
-
- if (Value *ConstVal = P->hasConstantValue()) {
- P->replaceAllUsesWith(ConstVal);
+
+ // FIXME: Provide DL, TLI, DT, AT to SimplifyInstruction.
+ if (Value *V = SimplifyInstruction(P)) {
+ 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
Pointer = cast<StoreInst>(I)->getPointerOperand();
-
+
if (isa<Constant>(Pointer)) return false;
-
+
Constant *C = LVI->getConstant(Pointer, I->getParent());
if (!C) return false;
-
+
++NumMemAccess;
I->replaceUsesOfWith(Pointer, C);
return true;
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;
-
- LazyValueInfo::Tristate Result = LVI->getPredicateOnEdge(C->getPredicate(),
+
+ LazyValueInfo::Tristate Result = LVI->getPredicateOnEdge(C->getPredicate(),
C->getOperand(0), Op1, *PI, C->getParent());
if (Result == LazyValueInfo::Unknown) return false;
++PI;
while (PI != PE) {
- LazyValueInfo::Tristate Res = LVI->getPredicateOnEdge(C->getPredicate(),
+ 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;
}
+/// 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);
+ // 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;
+}
+
bool CorrelatedValuePropagation::runOnFunction(Function &F) {
+ if (skipOptnoneFunction(F))
+ return false;
+
LVI = &getAnalysis<LazyValueInfo>();
-
+
bool FnChanged = false;
-
- // Perform a depth-first walk of the CFG so that we don't waste time
- // optimizing unreachable blocks.
- for (df_iterator<BasicBlock*> FI = df_begin(&F.getEntryBlock()),
- FE = df_end(&F.getEntryBlock()); FI != FE; ++FI) {
+
+ 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++;
break;
}
}
-
- // Propagating correlated values might leave cruft around.
- // Try to clean it up before we continue.
- if (BBChanged)
- SimplifyInstructionsInBlock(*FI);
-
+
+ Instruction *Term = FI->getTerminator();
+ switch (Term->getOpcode()) {
+ case Instruction::Switch:
+ BBChanged |= processSwitch(cast<SwitchInst>(Term));
+ break;
+ }
+
FnChanged |= BBChanged;
}
-
+
return FnChanged;
}
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