[flang] Don't duplicate impure function call for UBOUND() (#153648)

Because the per-dimension information in a descriptor holds an extent
and a lower bound, but not an upper bound, the calculation of the upper
bound sometimes requires that the extent and lower bound be extracted
from a descriptor and added together, minus 1. This shouldn't be
attempted when the NamedEntity of the descriptor is something that
shouldn't be duplicated and used twice; specifically, it shouldn't apply
to NamedEntities containing references to impure functions as parts of
subscript expressions.

Fixes https://github.com/llvm/llvm-project/issues/153031.

flang/include/flang/Evaluate/tools.h

@@ -1144,15 +1144,14 @@ std::optional<std::string> FindImpureCall(
 std::optional<std::string> FindImpureCall(
     FoldingContext &, const ProcedureRef &);
 
-// Predicate: is a scalar expression suitable for naive scalar expansion
+// Predicate: does an expression contain anything that would prevent it from
-// in the flattening of an array expression?
+// being duplicated so that two instances of it then appear in the same
-// TODO: capture such scalar expansions in temporaries, flatten everything
+// expression?
-class UnexpandabilityFindingVisitor
+class UnsafeToCopyVisitor : public AnyTraverse<UnsafeToCopyVisitor> {
-    : public AnyTraverse<UnexpandabilityFindingVisitor> {
 public:
-  using Base = AnyTraverse<UnexpandabilityFindingVisitor>;
+  using Base = AnyTraverse<UnsafeToCopyVisitor>;
   using Base::operator();
-  explicit UnexpandabilityFindingVisitor(bool admitPureCall)
+  explicit UnsafeToCopyVisitor(bool admitPureCall)
       : Base{*this}, admitPureCall_{admitPureCall} {}
   template <typename T> bool operator()(const FunctionRef<T> &procRef) {
     return !admitPureCall_ || !procRef.proc().IsPure();
@@ -1163,14 +1162,22 @@ private:
   bool admitPureCall_{false};
 };
 
+template <typename A>
+bool IsSafelyCopyable(const A &x, bool admitPureCall = false) {
+  return !UnsafeToCopyVisitor{admitPureCall}(x);
+}
+
+// Predicate: is a scalar expression suitable for naive scalar expansion
+// in the flattening of an array expression?
+// TODO: capture such scalar expansions in temporaries, flatten everything
 template <typename T>
 bool IsExpandableScalar(const Expr<T> &expr, FoldingContext &context,
     const Shape &shape, bool admitPureCall = false) {
-  if (UnexpandabilityFindingVisitor{admitPureCall}(expr)) {
+  if (IsSafelyCopyable(expr, admitPureCall)) {
+    return true;
+  } else {
     auto extents{AsConstantExtents(context, shape)};
     return extents && !HasNegativeExtent(*extents) && GetSize(*extents) == 1;
-  } else {
-    return true;
   }
 }
 

flang/lib/Evaluate/shape.cpp

@@ -623,7 +623,7 @@ MaybeExtentExpr GetRawUpperBound(
       } else if (semantics::IsAssumedSizeArray(symbol) &&
           dimension + 1 == symbol.Rank()) {
         return std::nullopt;
-      } else {
+      } else if (IsSafelyCopyable(base, /*admitPureCall=*/true)) {
         return ComputeUpperBound(
             GetRawLowerBound(base, dimension), GetExtent(base, dimension));
       }
@@ -678,11 +678,13 @@ static MaybeExtentExpr GetUBOUND(FoldingContext *context,
       } else if (semantics::IsAssumedSizeArray(symbol) &&
           dimension + 1 == symbol.Rank()) {
         return std::nullopt; // UBOUND() folding replaces with -1
-      } else if (auto lb{GetLBOUND(base, dimension, invariantOnly)}) {
+      } else if (IsSafelyCopyable(base, /*admitPureCall=*/true)) {
+        if (auto lb{GetLBOUND(base, dimension, invariantOnly)}) {
           return ComputeUpperBound(
               std::move(*lb), GetExtent(base, dimension, invariantOnly));
         }
       }
+    }
   } else if (const auto *assoc{
                  symbol.detailsIf<semantics::AssocEntityDetails>()}) {
     if (assoc->IsAssumedSize() || assoc->IsAssumedRank()) {

flang/test/Evaluate/bug153031.f90

@@ -0,0 +1,18 @@
+! RUN: %flang_fc1 -fdebug-unparse %s 2>&1 | FileCheck %s
+! Ensure that UBOUND() calculation from LBOUND()+SIZE() isn't applied to
+! variables containing references to impure functions.
+type t
+  real, allocatable :: a(:)
+end type
+interface
+  pure integer function pure(n)
+    integer, intent(in) :: n
+  end
+end interface
+type(t) :: x(10)
+allocate(x(1)%a(2))
+!CHECK: PRINT *, ubound(x(int(impure(1_4),kind=8))%a,dim=1_4)
+print *, ubound(x(impure(1))%a, dim=1)
+!CHECK: PRINT *, int(size(x(int(pure(1_4),kind=8))%a,dim=1,kind=8)+lbound(x(int(pure(1_4),kind=8))%a,dim=1,kind=8)-1_8,kind=4)
+print *, ubound(x(pure(1))%a, dim=1)
+end