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[flang] Fold character array constructor with unknown length #123983

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Merged
merged 1 commit into from
Jan 27, 2025
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[flang] Fold character array constructor with unknown length #123983

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22 changes: 16 additions & 6 deletions flang/lib/Evaluate/fold-implementation.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1263,19 +1263,22 @@ template <typename T> class ArrayConstructorFolder {
explicit ArrayConstructorFolder(FoldingContext &c) : context_{c} {}

Expr<T> FoldArray(ArrayConstructor<T> &&array) {
if constexpr (T::category == TypeCategory::Character) {
if (const auto *len{array.LEN()}) {
charLength_ = ToInt64(Fold(context_, common::Clone(*len)));
knownCharLength_ = charLength_.has_value();
}
}
// Calls FoldArray(const ArrayConstructorValues<T> &) below
if (FoldArray(array)) {
auto n{static_cast<ConstantSubscript>(elements_.size())};
if constexpr (std::is_same_v<T, SomeDerived>) {
return Expr<T>{Constant<T>{array.GetType().GetDerivedTypeSpec(),
std::move(elements_), ConstantSubscripts{n}}};
} else if constexpr (T::category == TypeCategory::Character) {
if (const auto *len{array.LEN()}) {
auto length{Fold(context_, common::Clone(*len))};
if (std::optional<ConstantSubscript> lengthValue{ToInt64(length)}) {
return Expr<T>{Constant<T>{
*lengthValue, std::move(elements_), ConstantSubscripts{n}}};
}
if (charLength_) {
return Expr<T>{Constant<T>{
*charLength_, std::move(elements_), ConstantSubscripts{n}}};
}
} else {
return Expr<T>{
Expand All @@ -1296,6 +1299,11 @@ template <typename T> class ArrayConstructorFolder {
elements_.emplace_back(c->At(index));
} while (c->IncrementSubscripts(index));
}
if constexpr (T::category == TypeCategory::Character) {
if (!knownCharLength_) {
charLength_ = std::max(c->LEN(), charLength_.value_or(-1));
}
}
return true;
} else {
return false;
Expand Down Expand Up @@ -1345,6 +1353,8 @@ template <typename T> class ArrayConstructorFolder {

FoldingContext &context_;
std::vector<Scalar<T>> elements_;
std::optional<ConstantSubscript> charLength_;
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What would be the case, when knownCharLength_ is false, but charLengh_ has value?

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knownCharLength_ is set true if and only if the character array constructor has an explicit length (from an explicit type specifier); in this case, the known length is dispositive and the element lengths don't matter. Otherwise, charLength_ can change when longer elements are encountered.

bool knownCharLength_{false};
};

template <typename T>
Expand Down
5 changes: 5 additions & 0 deletions flang/test/Evaluate/bug123766.f90
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@@ -0,0 +1,5 @@
! RUN: %python %S/test_folding.py %s %flang_fc1
character(10), parameter :: a = '0123456789'
character(3), parameter :: arr(3) = [(a(1:i), i=1,3)]
logical, parameter :: test1 = all(arr == ["0", "01", "012"])
end
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