//
//===----------------------------------------------------------------------===//
-#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"
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());
// Transform each operand.
for (SCEVNAryExpr::op_iterator I = AR->op_begin(), E = AR->op_end();
I != E; ++I) {
- const SCEV *O = *I;
- const SCEV *N = TransformForPostIncUse(Kind, O, LUser, 0, Loops, SE, DT);
- Operands.push_back(N);
+ Operands.push_back(TransformSubExpr(*I, LUser, nullptr));
}
- const SCEV *Result = SE.getAddRecExpr(Operands, L);
+ // Conservatively use AnyWrap until/unless we need FlagNW.
+ const SCEV *Result = SE.getAddRecExpr(Operands, L, SCEV::FlagAnyWrap);
switch (Kind) {
- default: llvm_unreachable("Unexpected transform name!");
case NormalizeAutodetect:
- if (IVUseShouldUsePostIncValue(User, OperandValToReplace, L, &DT)) {
+ // 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 =
- TransformForPostIncUse(Kind, AR->getStepRecurrence(SE),
- User, OperandValToReplace, Loops, SE, DT);
+ TransformSubExpr(AR->getStepRecurrence(SE),
+ User, OperandValToReplace);
Result = SE.getMinusSCEV(Result, TransformedStep);
Loops.insert(L);
}
-#ifdef XDEBUG
- assert(S == TransformForPostIncUse(Denormalize, Result,
- User, OperandValToReplace,
- Loops, SE, DT) &&
+#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 =
- TransformForPostIncUse(Kind, AR->getStepRecurrence(SE),
- User, OperandValToReplace, Loops, SE, DT);
+ TransformSubExpr(AR->getStepRecurrence(SE),
+ User, OperandValToReplace);
Result = SE.getMinusSCEV(Result, TransformedStep);
}
-#ifdef XDEBUG
- assert(S == TransformForPostIncUse(Denormalize, Result,
- User, OperandValToReplace,
- Loops, SE, DT) &&
+#if 0
+ // See the comment on the assert above.
+ assert(S == TransformSubExpr(Result, User, OperandValToReplace) &&
"SCEV normalization is not invertible!");
#endif
break;
case Denormalize:
- if (Loops.count(L))
- Result = cast<SCEVAddRecExpr>(Result)->getPostIncExpr(SE);
+ // 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;
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 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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