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-rw-r--r--lib/Analysis/ScalarEvolutionExpander.cpp191
1 files changed, 140 insertions, 51 deletions
diff --git a/lib/Analysis/ScalarEvolutionExpander.cpp b/lib/Analysis/ScalarEvolutionExpander.cpp
index fc66ddb6f4..7ebc00a19a 100644
--- a/lib/Analysis/ScalarEvolutionExpander.cpp
+++ b/lib/Analysis/ScalarEvolutionExpander.cpp
@@ -144,17 +144,89 @@ Value *SCEVExpander::InsertBinop(Instruction::BinaryOps Opcode, Value *LHS,
return BO;
}
+/// FactorOutConstant - Test if S is evenly divisible by Factor, using signed
+/// division. If so, update S with Factor divided out and return true.
+/// TODO: When ScalarEvolution gets a SCEVSDivExpr, this can be made
+/// unnecessary; in its place, just signed-divide Ops[i] by the scale and
+/// check to see if the divide was folded.
+static bool FactorOutConstant(SCEVHandle &S,
+ const APInt &Factor,
+ ScalarEvolution &SE) {
+ // Everything is divisible by one.
+ if (Factor == 1)
+ return true;
+
+ // For a Constant, check for a multiple of the given factor.
+ if (const SCEVConstant *C = dyn_cast<SCEVConstant>(S))
+ if (!C->getValue()->getValue().srem(Factor)) {
+ ConstantInt *CI =
+ ConstantInt::get(C->getValue()->getValue().sdiv(Factor));
+ SCEVHandle Div = SE.getConstant(CI);
+ S = Div;
+ return true;
+ }
+
+ // In a Mul, check if there is a constant operand which is a multiple
+ // of the given factor.
+ if (const SCEVMulExpr *M = dyn_cast<SCEVMulExpr>(S))
+ if (const SCEVConstant *C = dyn_cast<SCEVConstant>(M->getOperand(0)))
+ if (!C->getValue()->getValue().srem(Factor)) {
+ std::vector<SCEVHandle> NewMulOps(M->getOperands());
+ NewMulOps[0] =
+ SE.getConstant(C->getValue()->getValue().sdiv(Factor));
+ S = SE.getMulExpr(NewMulOps);
+ return true;
+ }
+
+ // In an AddRec, check if both start and step are divisible.
+ if (const SCEVAddRecExpr *A = dyn_cast<SCEVAddRecExpr>(S)) {
+ SCEVHandle Start = A->getStart();
+ if (!FactorOutConstant(Start, Factor, SE))
+ return false;
+ SCEVHandle Step = A->getStepRecurrence(SE);
+ if (!FactorOutConstant(Step, Factor, SE))
+ return false;
+ S = SE.getAddRecExpr(Start, Step, A->getLoop());
+ return true;
+ }
+
+ return false;
+}
+
/// expandAddToGEP - Expand a SCEVAddExpr with a pointer type into a GEP
-/// instead of using ptrtoint+arithmetic+inttoptr.
-Value *SCEVExpander::expandAddToGEP(const SCEVAddExpr *S,
+/// instead of using ptrtoint+arithmetic+inttoptr. This helps
+/// BasicAliasAnalysis analyze the result. However, it suffers from the
+/// underlying bug described in PR2831. Addition in LLVM currently always
+/// has two's complement wrapping guaranteed. However, the semantics for
+/// getelementptr overflow are ambiguous. In the common case though, this
+/// expansion gets used when a GEP in the original code has been converted
+/// into integer arithmetic, in which case the resulting code will be no
+/// more undefined than it was originally.
+///
+/// Design note: It might seem desirable for this function to be more
+/// loop-aware. If some of the indices are loop-invariant while others
+/// aren't, it might seem desirable to emit multiple GEPs, keeping the
+/// loop-invariant portions of the overall computation outside the loop.
+/// However, there are a few reasons this is not done here. Hoisting simple
+/// arithmetic is a low-level optimization that often isn't very
+/// important until late in the optimization process. In fact, passes
+/// like InstructionCombining will combine GEPs, even if it means
+/// pushing loop-invariant computation down into loops, so even if the
+/// GEPs were split here, the work would quickly be undone. The
+/// LoopStrengthReduction pass, which is usually run quite late (and
+/// after the last InstructionCombining pass), takes care of hoisting
+/// loop-invariant portions of expressions, after considering what
+/// can be folded using target addressing modes.
+///
+Value *SCEVExpander::expandAddToGEP(const SCEVHandle *op_begin,
+ const SCEVHandle *op_end,
const PointerType *PTy,
const Type *Ty,
Value *V) {
const Type *ElTy = PTy->getElementType();
SmallVector<Value *, 4> GepIndices;
- std::vector<SCEVHandle> Ops = S->getOperands();
+ std::vector<SCEVHandle> Ops(op_begin, op_end);
bool AnyNonZeroIndices = false;
- Ops.pop_back();
// Decend down the pointer's type and attempt to convert the other
// operands into GEP indices, at each level. The first index in a GEP
@@ -167,45 +239,27 @@ Value *SCEVExpander::expandAddToGEP(const SCEVAddExpr *S,
std::vector<SCEVHandle> NewOps;
std::vector<SCEVHandle> ScaledOps;
for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
+ // Split AddRecs up into parts as either of the parts may be usable
+ // without the other.
+ if (const SCEVAddRecExpr *A = dyn_cast<SCEVAddRecExpr>(Ops[i]))
+ if (!A->getStart()->isZero()) {
+ SCEVHandle Start = A->getStart();
+ Ops.push_back(SE.getAddRecExpr(SE.getIntegerSCEV(0, A->getType()),
+ A->getStepRecurrence(SE),
+ A->getLoop()));
+ Ops[i] = Start;
+ ++e;
+ }
+ // If the scale size is not 0, attempt to factor out a scale.
if (ElSize != 0) {
- // For a Constant, check for a multiple of the pointer type's
- // scale size.
- if (const SCEVConstant *C = dyn_cast<SCEVConstant>(Ops[i]))
- if (!C->getValue()->getValue().srem(ElSize)) {
- ConstantInt *CI =
- ConstantInt::get(C->getValue()->getValue().sdiv(ElSize));
- SCEVHandle Div = SE.getConstant(CI);
- ScaledOps.push_back(Div);
- continue;
- }
- // In a Mul, check if there is a constant operand which is a multiple
- // of the pointer type's scale size.
- if (const SCEVMulExpr *M = dyn_cast<SCEVMulExpr>(Ops[i]))
- if (const SCEVConstant *C = dyn_cast<SCEVConstant>(M->getOperand(0)))
- if (!C->getValue()->getValue().srem(ElSize)) {
- std::vector<SCEVHandle> NewMulOps(M->getOperands());
- NewMulOps[0] =
- SE.getConstant(C->getValue()->getValue().sdiv(ElSize));
- ScaledOps.push_back(SE.getMulExpr(NewMulOps));
- continue;
- }
- // In an Unknown, check if the underlying value is a Mul by a constant
- // which is equal to the pointer type's scale size.
- if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(Ops[i]))
- if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U->getValue()))
- if (BO->getOpcode() == Instruction::Mul)
- if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->getOperand(1)))
- if (CI->getValue() == ElSize) {
- ScaledOps.push_back(SE.getUnknown(BO->getOperand(0)));
- continue;
- }
- // If the pointer type's scale size is 1, no scaling is necessary
- // and any value can be used.
- if (ElSize == 1) {
- ScaledOps.push_back(Ops[i]);
+ SCEVHandle Op = Ops[i];
+ if (FactorOutConstant(Op, ElSize, SE)) {
+ ScaledOps.push_back(Op); // Op now has ElSize factored out.
continue;
}
}
+ // If the operand was not divisible, add it to the list of operands
+ // we'll scan next iteration.
NewOps.push_back(Ops[i]);
}
Ops = NewOps;
@@ -292,17 +346,14 @@ Value *SCEVExpander::visitAddExpr(const SCEVAddExpr *S) {
const Type *Ty = SE.getEffectiveSCEVType(S->getType());
Value *V = expand(S->getOperand(S->getNumOperands()-1));
- // Turn things like ptrtoint+arithmetic+inttoptr into GEP. This helps
- // BasicAliasAnalysis analyze the result. However, it suffers from the
- // underlying bug described in PR2831. Addition in LLVM currently always
- // has two's complement wrapping guaranteed. However, the semantics for
- // getelementptr overflow are ambiguous. In the common case though, this
- // expansion gets used when a GEP in the original code has been converted
- // into integer arithmetic, in which case the resulting code will be no
- // more undefined than it was originally.
+ // Turn things like ptrtoint+arithmetic+inttoptr into GEP. See the
+ // comments on expandAddToGEP for details.
if (SE.TD)
- if (const PointerType *PTy = dyn_cast<PointerType>(V->getType()))
- return expandAddToGEP(S, PTy, Ty, V);
+ if (const PointerType *PTy = dyn_cast<PointerType>(V->getType())) {
+ const std::vector<SCEVHandle> &Ops = S->getOperands();
+ return expandAddToGEP(Ops.data(), Ops.data() + Ops.size() - 1,
+ PTy, Ty, V);
+ }
V = InsertNoopCastOfTo(V, Ty);
@@ -357,6 +408,27 @@ Value *SCEVExpander::visitUDivExpr(const SCEVUDivExpr *S) {
return InsertBinop(Instruction::UDiv, LHS, RHS, InsertPt);
}
+/// Move parts of Base into Rest to leave Base with the minimal
+/// expression that provides a pointer operand suitable for a
+/// GEP expansion.
+static void ExposePointerBase(SCEVHandle &Base, SCEVHandle &Rest,
+ ScalarEvolution &SE) {
+ while (const SCEVAddRecExpr *A = dyn_cast<SCEVAddRecExpr>(Base)) {
+ Base = A->getStart();
+ Rest = SE.getAddExpr(Rest,
+ SE.getAddRecExpr(SE.getIntegerSCEV(0, A->getType()),
+ A->getStepRecurrence(SE),
+ A->getLoop()));
+ }
+ if (const SCEVAddExpr *A = dyn_cast<SCEVAddExpr>(Base)) {
+ Base = A->getOperand(A->getNumOperands()-1);
+ std::vector<SCEVHandle> NewAddOps(A->op_begin(), A->op_end());
+ NewAddOps.back() = Rest;
+ Rest = SE.getAddExpr(NewAddOps);
+ ExposePointerBase(Base, Rest, SE);
+ }
+}
+
Value *SCEVExpander::visitAddRecExpr(const SCEVAddRecExpr *S) {
const Type *Ty = SE.getEffectiveSCEVType(S->getType());
const Loop *L = S->getLoop();
@@ -365,8 +437,25 @@ Value *SCEVExpander::visitAddRecExpr(const SCEVAddRecExpr *S) {
if (!S->getStart()->isZero()) {
std::vector<SCEVHandle> NewOps(S->getOperands());
NewOps[0] = SE.getIntegerSCEV(0, Ty);
- Value *Rest = expand(SE.getAddRecExpr(NewOps, L));
- return expand(SE.getAddExpr(S->getStart(), SE.getUnknown(Rest)));
+ SCEVHandle Rest = SE.getAddRecExpr(NewOps, L);
+
+ // Turn things like ptrtoint+arithmetic+inttoptr into GEP. See the
+ // comments on expandAddToGEP for details.
+ if (SE.TD) {
+ SCEVHandle Base = S->getStart();
+ SCEVHandle RestArray[1] = Rest;
+ // Dig into the expression to find the pointer base for a GEP.
+ ExposePointerBase(Base, RestArray[0], SE);
+ // If we found a pointer, expand the AddRec with a GEP.
+ if (const PointerType *PTy = dyn_cast<PointerType>(Base->getType())) {
+ Value *StartV = expand(Base);
+ assert(StartV->getType() == PTy && "Pointer type mismatch for GEP!");
+ return expandAddToGEP(RestArray, RestArray+1, PTy, Ty, StartV);
+ }
+ }
+
+ Value *RestV = expand(Rest);
+ return expand(SE.getAddExpr(S->getStart(), SE.getUnknown(RestV)));
}
// {0,+,1} --> Insert a canonical induction variable into the loop!
generated by cgit v1.2.3-18-g5258 (git 2.32.0) at 2025-05-02 10:51:50 +0000