[flang] Fix crash in folding of DPROD() with non-scalar arguments

DPROD(x,y) is defined as DBLE(x)*DBLE(y) and that's exactly how
the implementation of its rewriting and possible folding should
be implemented, instead of the current code that only works when
both arguments are scalar and crashes otherwise.

Fixes llvm#63991.

Differential Revision: https://reviews.llvm.org/D156754

Author: klausler

flang/lib/Evaluate/fold-real.cpp

@@ -149,10 +149,15 @@ Expr<Type<TypeCategory::Real, KIND>> FoldIntrinsicFunction(
   } else if (name == "dot_product") {
     return FoldDotProduct<T>(context, std::move(funcRef));
   } else if (name == "dprod") {
-    if (auto scalars{GetScalarConstantArguments<T, T>(context, args)}) {
-      return Fold(context,
-          Expr<T>{Multiply<T>{
-              Expr<T>{std::get<0>(*scalars)}, Expr<T>{std::get<1>(*scalars)}}});
+    // Rewrite DPROD(x,y) -> DBLE(x)*DBLE(y)
+    if (args.at(0) && args.at(1)) {
+      const auto *xExpr{args[0]->UnwrapExpr()};
+      const auto *yExpr{args[1]->UnwrapExpr()};
+      if (xExpr && yExpr) {
+        return Fold(context,
+            ToReal<T::kind>(context, common::Clone(*xExpr)) *
+                ToReal<T::kind>(context, common::Clone(*yExpr)));
+      }
     }
   } else if (name == "epsilon") {
     return Expr<T>{Scalar<T>::EPSILON()};

flang/test/Evaluate/fold-dprod.f90

@@ -0,0 +1,8 @@
+! RUN: %python %S/test_folding.py %s %flang_fc1
+! Tests folding of DPROD()
+module m
+  logical, parameter :: test_kind = kind(dprod(2., 3.)) == kind(0.d0)
+  logical, parameter :: test_ss = dprod(2., 3.) == 6.d0
+  logical, parameter :: test_sv = all(dprod(2., [3.,4.]) == [6.d0,8.d0])
+  logical, parameter :: test_vv = all(dprod([2.,3.], [4.,5.]) == [8.d0,15.0d0])
+end