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[flang] Fix spurious error due to bad expression shape calculation #124323

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Jan 27, 2025
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[flang] Fix spurious error due to bad expression shape calculation #124323

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25 changes: 17 additions & 8 deletions flang/include/flang/Evaluate/shape.h
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Original file line number Diff line number Diff line change
Expand Up @@ -71,6 +71,9 @@ template <typename A>
std::optional<Shape> GetShape(
FoldingContext &, const A &, bool invariantOnly = true);
template <typename A>
std::optional<Shape> GetShape(
FoldingContext *, const A &, bool invariantOnly = true);
template <typename A>
std::optional<Shape> GetShape(const A &, bool invariantOnly = true);

// The dimension argument to these inquiries is zero-based,
Expand Down Expand Up @@ -149,6 +152,8 @@ inline MaybeExtentExpr GetSize(const std::optional<Shape> &maybeShape) {
// Utility predicate: does an expression reference any implied DO index?
bool ContainsAnyImpliedDoIndex(const ExtentExpr &);

// GetShape()
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Is this comment intentional?

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Yes. I like to have a comment like this appear before the implementation of a library function when that implementation is necessarily preceded by screens worth of helper functions and classes, so that it's clear that the code after the comment is leading up to something. I'm not always consistent about this, though.


class GetShapeHelper
: public AnyTraverse<GetShapeHelper, std::optional<Shape>> {
public:
Expand Down Expand Up @@ -261,23 +266,27 @@ class GetShapeHelper

template <typename A>
std::optional<Shape> GetShape(
FoldingContext &context, const A &x, bool invariantOnly) {
if (auto shape{GetShapeHelper{&context, invariantOnly}(x)}) {
return Fold(context, std::move(shape));
FoldingContext *context, const A &x, bool invariantOnly) {
if (auto shape{GetShapeHelper{context, invariantOnly}(x)}) {
if (context) {
return Fold(*context, std::move(shape));
} else {
return shape;
}
} else {
return std::nullopt;
}
}

template <typename A>
std::optional<Shape> GetShape(const A &x, bool invariantOnly) {
return GetShapeHelper{/*context=*/nullptr, invariantOnly}(x);
std::optional<Shape> GetShape(
FoldingContext &context, const A &x, bool invariantOnly) {
return GetShape(&context, x, invariantOnly);
}

template <typename A>
std::optional<Shape> GetShape(
FoldingContext *context, const A &x, bool invariantOnly = true) {
return GetShapeHelper{context, invariantOnly}(x);
std::optional<Shape> GetShape(const A &x, bool invariantOnly) {
return GetShape(/*context=*/nullptr, x, invariantOnly);
}

template <typename A>
Expand Down
13 changes: 10 additions & 3 deletions flang/lib/Evaluate/shape.cpp
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Expand Up @@ -16,13 +16,18 @@
#include "flang/Evaluate/tools.h"
#include "flang/Evaluate/type.h"
#include "flang/Parser/message.h"
#include "flang/Semantics/semantics.h"
#include "flang/Semantics/symbol.h"
#include <functional>

using namespace std::placeholders; // _1, _2, &c. for std::bind()

namespace Fortran::evaluate {

FoldingContext &GetFoldingContextFrom(const Symbol &symbol) {
return symbol.owner().context().foldingContext();
}

bool IsImpliedShape(const Symbol &original) {
const Symbol &symbol{ResolveAssociations(original)};
const auto *details{symbol.detailsIf<semantics::ObjectEntityDetails>()};
Expand Down Expand Up @@ -483,7 +488,7 @@ static MaybeExtentExpr GetAssociatedExtent(
const Symbol &symbol, int dimension) {
if (const auto *assoc{symbol.detailsIf<semantics::AssocEntityDetails>()};
assoc && !assoc->rank()) { // not SELECT RANK case
if (auto shape{GetShape(assoc->expr())};
if (auto shape{GetShape(GetFoldingContextFrom(symbol), assoc->expr())};
shape && dimension < static_cast<int>(shape->size())) {
if (auto &extent{shape->at(dimension)};
// Don't return a non-constant extent, as the variables that
Expand Down Expand Up @@ -519,7 +524,8 @@ MaybeExtentExpr GetExtent(
}
if (const auto *details{symbol.detailsIf<semantics::ObjectEntityDetails>()}) {
if (IsImpliedShape(symbol) && details->init()) {
if (auto shape{GetShape(symbol, invariantOnly)}) {
if (auto shape{
GetShape(GetFoldingContextFrom(symbol), symbol, invariantOnly)}) {
if (dimension < static_cast<int>(shape->size())) {
return std::move(shape->at(dimension));
}
Expand Down Expand Up @@ -568,7 +574,8 @@ MaybeExtentExpr GetExtent(const Subscript &subscript, const NamedEntity &base,
MaybeExtentExpr{triplet.stride()});
},
[&](const IndirectSubscriptIntegerExpr &subs) -> MaybeExtentExpr {
if (auto shape{GetShape(subs.value())};
if (auto shape{GetShape(
GetFoldingContextFrom(base.GetLastSymbol()), subs.value())};
shape && GetRank(*shape) == 1) {
// vector-valued subscript
return std::move(shape->at(0));
Expand Down
6 changes: 6 additions & 0 deletions flang/test/Evaluate/bug124191.f90
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@@ -0,0 +1,6 @@
! RUN: %flang_fc1 -fsyntax-only -pedantic %s 2>&1 | FileCheck --allow-empty %s
! CHECK-NOT: error:
! Regression test for https://github.com/llvm/llvm-project/issues/124191
character(3) :: arr(5) = ['aa.', 'bb.', 'cc.', 'dd.', 'ee.']
arr([(mod(iachar(arr(i:i-1:-1)(1:1)),5)+1, i=2,5,3)]) = arr(5:2:-1)
end
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