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NFC. Move out and expose affine expression simplification utility out of AffineOps lib #69813

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Oct 26, 2023
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NFC. Move out and expose affine expression simplification utility out of AffineOps lib #69813

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14 changes: 14 additions & 0 deletions mlir/include/mlir/IR/AffineExpr.h
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Original file line number Diff line number Diff line change
Expand Up @@ -353,6 +353,20 @@ void bindSymbolsList(MLIRContext *ctx, MutableArrayRef<AffineExprTy> exprs) {
e = getAffineSymbolExpr(idx++, ctx);
}

/// Get a lower or upper (depending on `isUpper`) bound for `expr` while using
/// the constant lower and upper bounds for its inputs provided in
/// `constLowerBounds` and `constUpperBounds`. Return std::nullopt if such a
/// bound can't be computed. This method only handles simple sum of product
/// expressions (w.r.t constant coefficients) so as to not depend on anything
/// heavyweight in `Analysis`. Expressions of the form: c0*d0 + c1*d1 + c2*s0 +
/// ... + c_n are handled. Expressions involving floordiv, ceildiv, mod or
/// semi-affine ones will lead a none being returned.
std::optional<int64_t>
getBoundForAffineExpr(AffineExpr expr, unsigned numDims, unsigned numSymbols,
ArrayRef<std::optional<int64_t>> constLowerBounds,
ArrayRef<std::optional<int64_t>> constUpperBounds,
bool isUpper);

} // namespace mlir

namespace llvm {
Expand Down
115 changes: 14 additions & 101 deletions mlir/lib/Dialect/Affine/IR/AffineOps.cpp
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Expand Up @@ -700,93 +700,6 @@ static std::optional<int64_t> getUpperBound(Value iv) {
return forOp.getConstantUpperBound() - 1;
}

/// Get a lower or upper (depending on `isUpper`) bound for `expr` while using
/// the constant lower and upper bounds for its inputs provided in
/// `constLowerBounds` and `constUpperBounds`. Return std::nullopt if such a
/// bound can't be computed. This method only handles simple sum of product
/// expressions (w.r.t constant coefficients) so as to not depend on anything
/// heavyweight in `Analysis`. Expressions of the form: c0*d0 + c1*d1 + c2*s0 +
/// ... + c_n are handled. Expressions involving floordiv, ceildiv, mod or
/// semi-affine ones will lead std::nullopt being returned.
static std::optional<int64_t>
getBoundForExpr(AffineExpr expr, unsigned numDims, unsigned numSymbols,
ArrayRef<std::optional<int64_t>> constLowerBounds,
ArrayRef<std::optional<int64_t>> constUpperBounds,
bool isUpper) {
// Handle divs and mods.
if (auto binOpExpr = expr.dyn_cast<AffineBinaryOpExpr>()) {
// If the LHS of a floor or ceil is bounded and the RHS is a constant, we
// can compute an upper bound.
if (binOpExpr.getKind() == AffineExprKind::FloorDiv) {
auto rhsConst = binOpExpr.getRHS().dyn_cast<AffineConstantExpr>();
if (!rhsConst || rhsConst.getValue() < 1)
return std::nullopt;
auto bound = getBoundForExpr(binOpExpr.getLHS(), numDims, numSymbols,
constLowerBounds, constUpperBounds, isUpper);
if (!bound)
return std::nullopt;
return mlir::floorDiv(*bound, rhsConst.getValue());
}
if (binOpExpr.getKind() == AffineExprKind::CeilDiv) {
auto rhsConst = binOpExpr.getRHS().dyn_cast<AffineConstantExpr>();
if (rhsConst && rhsConst.getValue() >= 1) {
auto bound =
getBoundForExpr(binOpExpr.getLHS(), numDims, numSymbols,
constLowerBounds, constUpperBounds, isUpper);
if (!bound)
return std::nullopt;
return mlir::ceilDiv(*bound, rhsConst.getValue());
}
return std::nullopt;
}
if (binOpExpr.getKind() == AffineExprKind::Mod) {
// lhs mod c is always <= c - 1 and non-negative. In addition, if `lhs` is
// bounded such that lb <= lhs <= ub and lb floordiv c == ub floordiv c
// (same "interval"), then lb mod c <= lhs mod c <= ub mod c.
auto rhsConst = binOpExpr.getRHS().dyn_cast<AffineConstantExpr>();
if (rhsConst && rhsConst.getValue() >= 1) {
int64_t rhsConstVal = rhsConst.getValue();
auto lb = getBoundForExpr(binOpExpr.getLHS(), numDims, numSymbols,
constLowerBounds, constUpperBounds,
/*isUpper=*/false);
auto ub = getBoundForExpr(binOpExpr.getLHS(), numDims, numSymbols,
constLowerBounds, constUpperBounds, isUpper);
if (ub && lb &&
floorDiv(*lb, rhsConstVal) == floorDiv(*ub, rhsConstVal))
return isUpper ? mod(*ub, rhsConstVal) : mod(*lb, rhsConstVal);
return isUpper ? rhsConstVal - 1 : 0;
}
}
}
// Flatten the expression.
SimpleAffineExprFlattener flattener(numDims, numSymbols);
flattener.walkPostOrder(expr);
ArrayRef<int64_t> flattenedExpr = flattener.operandExprStack.back();
// TODO: Handle local variables. We can get hold of flattener.localExprs and
// get bound on the local expr recursively.
if (flattener.numLocals > 0)
return std::nullopt;
int64_t bound = 0;
// Substitute the constant lower or upper bound for the dimensional or
// symbolic input depending on `isUpper` to determine the bound.
for (unsigned i = 0, e = numDims + numSymbols; i < e; ++i) {
if (flattenedExpr[i] > 0) {
auto &constBound = isUpper ? constUpperBounds[i] : constLowerBounds[i];
if (!constBound)
return std::nullopt;
bound += *constBound * flattenedExpr[i];
} else if (flattenedExpr[i] < 0) {
auto &constBound = isUpper ? constLowerBounds[i] : constUpperBounds[i];
if (!constBound)
return std::nullopt;
bound += *constBound * flattenedExpr[i];
}
}
// Constant term.
bound += flattenedExpr.back();
return bound;
}

/// Determine a constant upper bound for `expr` if one exists while exploiting
/// values in `operands`. Note that the upper bound is an inclusive one. `expr`
/// is guaranteed to be less than or equal to it.
Expand All @@ -805,9 +718,9 @@ static std::optional<int64_t> getUpperBound(AffineExpr expr, unsigned numDims,
if (auto constExpr = expr.dyn_cast<AffineConstantExpr>())
return constExpr.getValue();

return getBoundForExpr(expr, numDims, numSymbols, constLowerBounds,
constUpperBounds,
/*isUpper=*/true);
return getBoundForAffineExpr(expr, numDims, numSymbols, constLowerBounds,
constUpperBounds,
/*isUpper=*/true);
}

/// Determine a constant lower bound for `expr` if one exists while exploiting
Expand All @@ -829,9 +742,9 @@ static std::optional<int64_t> getLowerBound(AffineExpr expr, unsigned numDims,
if (auto constExpr = expr.dyn_cast<AffineConstantExpr>()) {
lowerBound = constExpr.getValue();
} else {
lowerBound = getBoundForExpr(expr, numDims, numSymbols, constLowerBounds,
constUpperBounds,
/*isUpper=*/false);
lowerBound = getBoundForAffineExpr(expr, numDims, numSymbols,
constLowerBounds, constUpperBounds,
/*isUpper=*/false);
}
return lowerBound;
}
Expand Down Expand Up @@ -970,14 +883,14 @@ static void simplifyMinOrMaxExprWithOperands(AffineMap &map,
lowerBounds.push_back(constExpr.getValue());
upperBounds.push_back(constExpr.getValue());
} else {
lowerBounds.push_back(getBoundForExpr(e, map.getNumDims(),
map.getNumSymbols(),
constLowerBounds, constUpperBounds,
/*isUpper=*/false));
upperBounds.push_back(getBoundForExpr(e, map.getNumDims(),
map.getNumSymbols(),
constLowerBounds, constUpperBounds,
/*isUpper=*/true));
lowerBounds.push_back(
getBoundForAffineExpr(e, map.getNumDims(), map.getNumSymbols(),
constLowerBounds, constUpperBounds,
/*isUpper=*/false));
upperBounds.push_back(
getBoundForAffineExpr(e, map.getNumDims(), map.getNumSymbols(),
constLowerBounds, constUpperBounds,
/*isUpper=*/true));
}
}

Expand Down
80 changes: 80 additions & 0 deletions mlir/lib/IR/AffineExpr.cpp
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Expand Up @@ -1438,3 +1438,83 @@ AffineExpr mlir::simplifyAffineExpr(AffineExpr expr, unsigned numDims,
assert(flattener.operandExprStack.empty());
return simplifiedExpr;
}

std::optional<int64_t> mlir::getBoundForAffineExpr(
AffineExpr expr, unsigned numDims, unsigned numSymbols,
ArrayRef<std::optional<int64_t>> constLowerBounds,
ArrayRef<std::optional<int64_t>> constUpperBounds, bool isUpper) {
// Handle divs and mods.
if (auto binOpExpr = expr.dyn_cast<AffineBinaryOpExpr>()) {
// If the LHS of a floor or ceil is bounded and the RHS is a constant, we
// can compute an upper bound.
if (binOpExpr.getKind() == AffineExprKind::FloorDiv) {
auto rhsConst = binOpExpr.getRHS().dyn_cast<AffineConstantExpr>();
if (!rhsConst || rhsConst.getValue() < 1)
return std::nullopt;
auto bound =
getBoundForAffineExpr(binOpExpr.getLHS(), numDims, numSymbols,
constLowerBounds, constUpperBounds, isUpper);
if (!bound)
return std::nullopt;
return mlir::floorDiv(*bound, rhsConst.getValue());
}
if (binOpExpr.getKind() == AffineExprKind::CeilDiv) {
auto rhsConst = binOpExpr.getRHS().dyn_cast<AffineConstantExpr>();
if (rhsConst && rhsConst.getValue() >= 1) {
auto bound =
getBoundForAffineExpr(binOpExpr.getLHS(), numDims, numSymbols,
constLowerBounds, constUpperBounds, isUpper);
if (!bound)
return std::nullopt;
return mlir::ceilDiv(*bound, rhsConst.getValue());
}
return std::nullopt;
}
if (binOpExpr.getKind() == AffineExprKind::Mod) {
// lhs mod c is always <= c - 1 and non-negative. In addition, if `lhs` is
// bounded such that lb <= lhs <= ub and lb floordiv c == ub floordiv c
// (same "interval"), then lb mod c <= lhs mod c <= ub mod c.
auto rhsConst = binOpExpr.getRHS().dyn_cast<AffineConstantExpr>();
if (rhsConst && rhsConst.getValue() >= 1) {
int64_t rhsConstVal = rhsConst.getValue();
auto lb = getBoundForAffineExpr(binOpExpr.getLHS(), numDims, numSymbols,
constLowerBounds, constUpperBounds,
/*isUpper=*/false);
auto ub =
getBoundForAffineExpr(binOpExpr.getLHS(), numDims, numSymbols,
constLowerBounds, constUpperBounds, isUpper);
if (ub && lb &&
floorDiv(*lb, rhsConstVal) == floorDiv(*ub, rhsConstVal))
return isUpper ? mod(*ub, rhsConstVal) : mod(*lb, rhsConstVal);
return isUpper ? rhsConstVal - 1 : 0;
}
}
}
// Flatten the expression.
SimpleAffineExprFlattener flattener(numDims, numSymbols);
flattener.walkPostOrder(expr);
ArrayRef<int64_t> flattenedExpr = flattener.operandExprStack.back();
// TODO: Handle local variables. We can get hold of flattener.localExprs and
// get bound on the local expr recursively.
if (flattener.numLocals > 0)
return std::nullopt;
int64_t bound = 0;
// Substitute the constant lower or upper bound for the dimensional or
// symbolic input depending on `isUpper` to determine the bound.
for (unsigned i = 0, e = numDims + numSymbols; i < e; ++i) {
if (flattenedExpr[i] > 0) {
auto &constBound = isUpper ? constUpperBounds[i] : constLowerBounds[i];
if (!constBound)
return std::nullopt;
bound += *constBound * flattenedExpr[i];
} else if (flattenedExpr[i] < 0) {
auto &constBound = isUpper ? constLowerBounds[i] : constUpperBounds[i];
if (!constBound)
return std::nullopt;
bound += *constBound * flattenedExpr[i];
}
}
// Constant term.
bound += flattenedExpr.back();
return bound;
}