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Extend the ValuesAtScope cache to cover all expressions, not just 

SCEVUnknowns, as the non-SCEVUnknown cases in the getSCEVAtScope code
can also end up repeatedly climing through the same expression trees,
which can be unusably slow when the trees are very tall.

Also, add a quick check for SCEV pointer equality to the main
SCEV comparison routine, as the full comparison code can be expensive
in the case of large expression trees.

These fix compile-time problems in some pathlogical cases.

llvm-svn: 80623
This commit is contained in:
Dan Gohman 2009-08-31 21:15:23 +00:00
parent f04db57674
commit cc2f1eb7fe
2 changed files with 34 additions and 24 deletions
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14
llvm/include/llvm/Analysis/ScalarEvolution.h
View File

@ -219,10 +219,11 @@ namespace llvm {
/// exit value.
std::map<PHINode*, Constant*> ConstantEvolutionLoopExitValue;
/// ValuesAtScopes - This map contains entries for all the instructions
/// that we attempt to compute getSCEVAtScope information for without
/// using SCEV techniques, which can be expensive.
std::map<Instruction *, std::map<const Loop *, Constant *> > ValuesAtScopes;
/// ValuesAtScopes - This map contains entries for all the expressions
/// that we attempt to compute getSCEVAtScope information for, which can
/// be expensive in extreme cases.
std::map<const SCEV *,
std::map<const Loop *, const SCEV *> > ValuesAtScopes;
/// createSCEV - We know that there is no SCEV for the specified value.
/// Analyze the expression.
@ -236,6 +237,11 @@ namespace llvm {
/// SCEVs.
const SCEV *createNodeForGEP(Operator *GEP);
/// computeSCEVAtScope - Implementation code for getSCEVAtScope; called
/// at most once for each SCEV+Loop pair.
///
const SCEV *computeSCEVAtScope(const SCEV *S, const Loop *L);
/// ForgetSymbolicValue - This looks up computed SCEV values for all
/// instructions that depend on the given instruction and removes them from
/// the Scalars map if they reference SymName. This is used during PHI

44
llvm/lib/Analysis/ScalarEvolution.cpp
View File

@ -385,6 +385,10 @@ namespace {
explicit SCEVComplexityCompare(LoopInfo *li) : LI(li) {}
bool operator()(const SCEV *LHS, const SCEV *RHS) const {
// Fast-path: SCEVs are uniqued so we can do a quick equality check.
if (LHS == RHS)
return false;
// Primarily, sort the SCEVs by their getSCEVType().
if (LHS->getSCEVType() != RHS->getSCEVType())
return LHS->getSCEVType() < RHS->getSCEVType();
@ -2420,9 +2424,10 @@ ScalarEvolution::ForgetSymbolicName(Instruction *I, const SCEV *SymName) {
// count information isn't going to change anything. In the later
// case, createNodeForPHI will perform the necessary updates on its
// own when it gets to that point.
if (!isa<PHINode>(I) || !isa<SCEVUnknown>(It->second))
if (!isa<PHINode>(I) || !isa<SCEVUnknown>(It->second)) {
ValuesAtScopes.erase(It->second);
Scalars.erase(It);
ValuesAtScopes.erase(I);
}
}
PushDefUseChildren(I, Worklist);
@ -3232,9 +3237,10 @@ ScalarEvolution::getBackedgeTakenInfo(const Loop *L) {
// count information isn't going to change anything. In the later
// case, createNodeForPHI will perform the necessary updates on its
// own when it gets to that point.
if (!isa<PHINode>(I) || !isa<SCEVUnknown>(It->second))
if (!isa<PHINode>(I) || !isa<SCEVUnknown>(It->second)) {
ValuesAtScopes.erase(It->second);
Scalars.erase(It);
ValuesAtScopes.erase(I);
}
if (PHINode *PN = dyn_cast<PHINode>(I))
ConstantEvolutionLoopExitValue.erase(PN);
}
@ -3264,8 +3270,8 @@ void ScalarEvolution::forgetLoopBackedgeTakenCount(const Loop *L) {
std::map<SCEVCallbackVH, const SCEV*>::iterator It =
Scalars.find(static_cast<Value *>(I));
if (It != Scalars.end()) {
ValuesAtScopes.erase(It->second);
Scalars.erase(It);
ValuesAtScopes.erase(I);
if (PHINode *PN = dyn_cast<PHINode>(I))
ConstantEvolutionLoopExitValue.erase(PN);
}
@ -3897,8 +3903,20 @@ ScalarEvolution::ComputeBackedgeTakenCountExhaustively(const Loop *L,
/// In the case that a relevant loop exit value cannot be computed, the
/// original value V is returned.
const SCEV *ScalarEvolution::getSCEVAtScope(const SCEV *V, const Loop *L) {
// FIXME: this should be turned into a virtual method on SCEV!
// Check to see if we've folded this expression at this loop before.
std::map<const Loop *, const SCEV *> &Values = ValuesAtScopes[V];
std::pair<std::map<const Loop *, const SCEV *>::iterator, bool> Pair =
Values.insert(std::make_pair(L, static_cast<const SCEV *>(0)));
if (!Pair.second)
return Pair.first->second ? Pair.first->second : V;
// Otherwise compute it.
const SCEV *C = computeSCEVAtScope(V, L);
Pair.first->second = C;
return C;
}
const SCEV *ScalarEvolution::computeSCEVAtScope(const SCEV *V, const Loop *L) {
if (isa<SCEVConstant>(V)) return V;
// If this instruction is evolved from a constant-evolving PHI, compute the
@ -3931,13 +3949,6 @@ const SCEV *ScalarEvolution::getSCEVAtScope(const SCEV *V, const Loop *L) {
// the arguments into constants, and if so, try to constant propagate the
// result. This is particularly useful for computing loop exit values.
if (CanConstantFold(I)) {
// Check to see if we've folded this instruction at this loop before.
std::map<const Loop *, Constant *> &Values = ValuesAtScopes[I];
std::pair<std::map<const Loop *, Constant *>::iterator, bool> Pair =
Values.insert(std::make_pair(L, static_cast<Constant *>(0)));
if (!Pair.second)
return Pair.first->second ? &*getSCEV(Pair.first->second) : V;
std::vector<Constant*> Operands;
Operands.reserve(I->getNumOperands());
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
@ -3986,7 +3997,6 @@ const SCEV *ScalarEvolution::getSCEVAtScope(const SCEV *V, const Loop *L) {
C = ConstantFoldInstOperands(I->getOpcode(), I->getType(),
&Operands[0], Operands.size(),
getContext());
Pair.first->second = C;
return getSCEV(C);
}
}
@ -5031,8 +5041,6 @@ void ScalarEvolution::SCEVCallbackVH::deleted() {
assert(SE && "SCEVCallbackVH called with a null ScalarEvolution!");
if (PHINode *PN = dyn_cast<PHINode>(getValPtr()))
SE->ConstantEvolutionLoopExitValue.erase(PN);
if (Instruction *I = dyn_cast<Instruction>(getValPtr()))
SE->ValuesAtScopes.erase(I);
SE->Scalars.erase(getValPtr());
// this now dangles!
}
@ -5062,8 +5070,6 @@ void ScalarEvolution::SCEVCallbackVH::allUsesReplacedWith(Value *) {
continue;
if (PHINode *PN = dyn_cast<PHINode>(U))
SE->ConstantEvolutionLoopExitValue.erase(PN);
if (Instruction *I = dyn_cast<Instruction>(U))
SE->ValuesAtScopes.erase(I);
SE->Scalars.erase(U);
for (Value::use_iterator UI = U->use_begin(), UE = U->use_end();
UI != UE; ++UI)
@ -5073,8 +5079,6 @@ void ScalarEvolution::SCEVCallbackVH::allUsesReplacedWith(Value *) {
if (DeleteOld) {
if (PHINode *PN = dyn_cast<PHINode>(Old))
SE->ConstantEvolutionLoopExitValue.erase(PN);
if (Instruction *I = dyn_cast<Instruction>(Old))
SE->ValuesAtScopes.erase(I);
SE->Scalars.erase(Old);
// this now dangles!
}