//
//===----------------------------------------------------------------------===//
-#include "llvm/Analysis/Dominators.h"
+#include "llvm/IR/Dominators.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/ScalarEvolutionNormalization.h"
/// post-inc value when we cannot) or it can end up adding extra live-ranges to
/// the loop, resulting in reg-reg copies (if we use the pre-inc value when we
/// should use the post-inc value).
-static bool IVUseShouldUsePostIncValue(Instruction *User, Instruction *IV,
+static bool IVUseShouldUsePostIncValue(Instruction *User, Value *Operand,
const Loop *L, DominatorTree *DT) {
// If the user is in the loop, use the preinc value.
if (L->contains(User)) return false;
// their uses occur in the predecessor block, not the block the PHI lives in)
// should still use the post-inc value. Check for this case now.
PHINode *PN = dyn_cast<PHINode>(User);
- if (!PN) return false; // not a phi, not dominated by latch block.
+ if (!PN || !Operand) return false; // not a phi, not dominated by latch block.
- // Look at all of the uses of IV by the PHI node. If any use corresponds to
- // a block that is not dominated by the latch block, give up and use the
+ // Look at all of the uses of Operand by the PHI node. If any use corresponds
+ // to a block that is not dominated by the latch block, give up and use the
// preincremented value.
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
- if (PN->getIncomingValue(i) == IV &&
+ if (PN->getIncomingValue(i) == Operand &&
!DT->dominates(LatchBlock, PN->getIncomingBlock(i)))
return false;
- // Okay, all uses of IV by PN are in predecessor blocks that really are
+ // Okay, all uses of Operand by PN are in predecessor blocks that really are
// dominated by the latch block. Use the post-incremented value.
return true;
}
-const SCEV *llvm::TransformForPostIncUse(TransformKind Kind,
- const SCEV *S,
- Instruction *User,
- Value *OperandValToReplace,
- PostIncLoopSet &Loops,
- ScalarEvolution &SE,
- DominatorTree &DT) {
- if (isa<SCEVConstant>(S) || isa<SCEVUnknown>(S))
- return S;
+namespace {
+
+/// Hold the state used during post-inc expression transformation, including a
+/// map of transformed expressions.
+class PostIncTransform {
+ TransformKind Kind;
+ PostIncLoopSet &Loops;
+ ScalarEvolution &SE;
+ DominatorTree &DT;
+
+ DenseMap<const SCEV*, const SCEV*> Transformed;
+
+public:
+ PostIncTransform(TransformKind kind, PostIncLoopSet &loops,
+ ScalarEvolution &se, DominatorTree &dt):
+ Kind(kind), Loops(loops), SE(se), DT(dt) {}
+
+ const SCEV *TransformSubExpr(const SCEV *S, Instruction *User,
+ Value *OperandValToReplace);
+
+protected:
+ const SCEV *TransformImpl(const SCEV *S, Instruction *User,
+ Value *OperandValToReplace);
+};
+
+} // namespace
+
+/// Implement post-inc transformation for all valid expression types.
+const SCEV *PostIncTransform::
+TransformImpl(const SCEV *S, Instruction *User, Value *OperandValToReplace) {
if (const SCEVCastExpr *X = dyn_cast<SCEVCastExpr>(S)) {
const SCEV *O = X->getOperand();
- const SCEV *N = TransformForPostIncUse(Kind, O, User, OperandValToReplace,
- Loops, SE, DT);
+ const SCEV *N = TransformSubExpr(O, User, OperandValToReplace);
if (O != N)
switch (S->getSCEVType()) {
case scZeroExtend: return SE.getZeroExtendExpr(N, S->getType());
return S;
}
+ if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
+ // An addrec. This is the interesting part.
+ SmallVector<const SCEV *, 8> Operands;
+ const Loop *L = AR->getLoop();
+ // The addrec conceptually uses its operands at loop entry.
+ Instruction *LUser = &L->getHeader()->front();
+ // Transform each operand.
+ for (SCEVNAryExpr::op_iterator I = AR->op_begin(), E = AR->op_end();
+ I != E; ++I) {
+ Operands.push_back(TransformSubExpr(*I, LUser, nullptr));
+ }
+ // Conservatively use AnyWrap until/unless we need FlagNW.
+ const SCEV *Result = SE.getAddRecExpr(Operands, L, SCEV::FlagAnyWrap);
+ switch (Kind) {
+ case NormalizeAutodetect:
+ // Normalize this SCEV by subtracting the expression for the final step.
+ // We only allow affine AddRecs to be normalized, otherwise we would not
+ // be able to correctly denormalize.
+ // e.g. {1,+,3,+,2} == {-2,+,1,+,2} + {3,+,2}
+ // Normalized form: {-2,+,1,+,2}
+ // Denormalized form: {1,+,3,+,2}
+ //
+ // However, denormalization would use a different step expression than
+ // normalization (see getPostIncExpr), generating the wrong final
+ // expression: {-2,+,1,+,2} + {1,+,2} => {-1,+,3,+,2}
+ if (AR->isAffine() &&
+ IVUseShouldUsePostIncValue(User, OperandValToReplace, L, &DT)) {
+ const SCEV *TransformedStep =
+ TransformSubExpr(AR->getStepRecurrence(SE),
+ User, OperandValToReplace);
+ Result = SE.getMinusSCEV(Result, TransformedStep);
+ Loops.insert(L);
+ }
+#if 0
+ // This assert is conceptually correct, but ScalarEvolution currently
+ // sometimes fails to canonicalize two equal SCEVs to exactly the same
+ // form. It's possibly a pessimization when this happens, but it isn't a
+ // correctness problem, so disable this assert for now.
+ assert(S == TransformSubExpr(Result, User, OperandValToReplace) &&
+ "SCEV normalization is not invertible!");
+#endif
+ break;
+ case Normalize:
+ // We want to normalize step expression, because otherwise we might not be
+ // able to denormalize to the original expression.
+ //
+ // Here is an example what will happen if we don't normalize step:
+ // ORIGINAL ISE:
+ // {(100 /u {1,+,1}<%bb16>),+,(100 /u {1,+,1}<%bb16>)}<%bb25>
+ // NORMALIZED ISE:
+ // {((-1 * (100 /u {1,+,1}<%bb16>)) + (100 /u {0,+,1}<%bb16>)),+,
+ // (100 /u {0,+,1}<%bb16>)}<%bb25>
+ // DENORMALIZED BACK ISE:
+ // {((2 * (100 /u {1,+,1}<%bb16>)) + (-1 * (100 /u {2,+,1}<%bb16>))),+,
+ // (100 /u {1,+,1}<%bb16>)}<%bb25>
+ // Note that the initial value changes after normalization +
+ // denormalization, which isn't correct.
+ if (Loops.count(L)) {
+ const SCEV *TransformedStep =
+ TransformSubExpr(AR->getStepRecurrence(SE),
+ User, OperandValToReplace);
+ Result = SE.getMinusSCEV(Result, TransformedStep);
+ }
+#if 0
+ // See the comment on the assert above.
+ assert(S == TransformSubExpr(Result, User, OperandValToReplace) &&
+ "SCEV normalization is not invertible!");
+#endif
+ break;
+ case Denormalize:
+ // Here we want to normalize step expressions for the same reasons, as
+ // stated above.
+ if (Loops.count(L)) {
+ const SCEV *TransformedStep =
+ TransformSubExpr(AR->getStepRecurrence(SE),
+ User, OperandValToReplace);
+ Result = SE.getAddExpr(Result, TransformedStep);
+ }
+ break;
+ }
+ return Result;
+ }
+
if (const SCEVNAryExpr *X = dyn_cast<SCEVNAryExpr>(S)) {
SmallVector<const SCEV *, 8> Operands;
bool Changed = false;
for (SCEVNAryExpr::op_iterator I = X->op_begin(), E = X->op_end();
I != E; ++I) {
const SCEV *O = *I;
- const SCEV *N = TransformForPostIncUse(Kind, O, User, OperandValToReplace,
- Loops, SE, DT);
+ const SCEV *N = TransformSubExpr(O, User, OperandValToReplace);
Changed |= N != O;
Operands.push_back(N);
}
- if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
- // An addrec. This is the interesting part.
- const Loop *L = AR->getLoop();
- const SCEV *Result = SE.getAddRecExpr(Operands, L);
- switch (Kind) {
- default: llvm_unreachable("Unexpected transform name!");
- case NormalizeAutodetect:
- if (Instruction *OI = dyn_cast<Instruction>(OperandValToReplace))
- if (IVUseShouldUsePostIncValue(User, OI, L, &DT)) {
- const SCEV *TransformedStep =
- TransformForPostIncUse(Kind, AR->getStepRecurrence(SE),
- User, OperandValToReplace, Loops, SE, DT);
- Result = SE.getMinusSCEV(Result, TransformedStep);
- Loops.insert(L);
- }
- break;
- case Normalize:
- if (Loops.count(L)) {
- const SCEV *TransformedStep =
- TransformForPostIncUse(Kind, AR->getStepRecurrence(SE),
- User, OperandValToReplace, Loops, SE, DT);
- Result = SE.getMinusSCEV(Result, TransformedStep);
- }
- break;
- case Denormalize:
- if (Loops.count(L))
- Result = SE.getAddExpr(Result, AR->getStepRecurrence(SE));
- break;
- }
- return Result;
- }
+ // If any operand actually changed, return a transformed result.
if (Changed)
switch (S->getSCEVType()) {
case scAddExpr: return SE.getAddExpr(Operands);
if (const SCEVUDivExpr *X = dyn_cast<SCEVUDivExpr>(S)) {
const SCEV *LO = X->getLHS();
const SCEV *RO = X->getRHS();
- const SCEV *LN = TransformForPostIncUse(Kind, LO, User, OperandValToReplace,
- Loops, SE, DT);
- const SCEV *RN = TransformForPostIncUse(Kind, RO, User, OperandValToReplace,
- Loops, SE, DT);
+ const SCEV *LN = TransformSubExpr(LO, User, OperandValToReplace);
+ const SCEV *RN = TransformSubExpr(RO, User, OperandValToReplace);
if (LO != LN || RO != RN)
return SE.getUDivExpr(LN, RN);
return S;
}
llvm_unreachable("Unexpected SCEV kind!");
- return 0;
+}
+
+/// Manage recursive transformation across an expression DAG. Revisiting
+/// expressions would lead to exponential recursion.
+const SCEV *PostIncTransform::
+TransformSubExpr(const SCEV *S, Instruction *User, Value *OperandValToReplace) {
+
+ if (isa<SCEVConstant>(S) || isa<SCEVUnknown>(S))
+ return S;
+
+ const SCEV *Result = Transformed.lookup(S);
+ if (Result)
+ return Result;
+
+ Result = TransformImpl(S, User, OperandValToReplace);
+ Transformed[S] = Result;
+ return Result;
+}
+
+/// Top level driver for transforming an expression DAG into its requested
+/// post-inc form (either "Normalized" or "Denormalized").
+const SCEV *llvm::TransformForPostIncUse(TransformKind Kind,
+ const SCEV *S,
+ Instruction *User,
+ Value *OperandValToReplace,
+ PostIncLoopSet &Loops,
+ ScalarEvolution &SE,
+ DominatorTree &DT) {
+ PostIncTransform Transform(Kind, Loops, SE, DT);
+ return Transform.TransformSubExpr(S, User, OperandValToReplace);
}
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