[flang] When folding FINDLOC, convert operands to a common type

For example, FINDLOC(A,X) should convert both A and X to COMPLEX(8)
if the operands are REAL(8) and COMPLEX(4), so that comparisons
can be done without losing inforation.  The current implementation
unconditionally converts X to the type of the array A.

Differential Revision: https://reviews.llvm.org/D127030

Author: klausler

flang/include/flang/Evaluate/type.h

@@ -452,6 +452,12 @@ int SelectedIntKind(std::int64_t precision = 0);
 int SelectedRealKind(
     std::int64_t precision = 0, std::int64_t range = 0, std::int64_t radix = 2);
 
+// Given the dynamic types and kinds of two operands, determine the common
+// type to which they must be converted in order to be compared with
+// intrinsic OPERATOR(==) or .EQV.
+std::optional<DynamicType> ComparisonType(
+    const DynamicType &, const DynamicType &);
+
 // For generating "[extern] template class", &c. boilerplate
 #define EXPAND_FOR_EACH_INTEGER_KIND(M, P, S) \
   M(P, S, 1) M(P, S, 2) M(P, S, 4) M(P, S, 8) M(P, S, 16)

flang/lib/Evaluate/fold-integer.cpp

@@ -436,6 +436,17 @@ static std::optional<Constant<SubscriptInteger>> FoldLocationCall(
     ActualArguments &arg, FoldingContext &context) {
   if (arg[0]) {
     if (auto type{arg[0]->GetType()}) {
+      if constexpr (which == WhichLocation::Findloc) {
+        // Both ARRAY and VALUE are susceptible to conversion to a common
+        // comparison type.
+        if (arg[1]) {
+          if (auto valType{arg[1]->GetType()}) {
+            if (auto compareType{ComparisonType(*type, *valType)}) {
+              type = compareType;
+            }
+          }
+        }
+      }
       return common::SearchTypes(
           LocationHelper<which>{std::move(*type), arg, context});
     }

flang/lib/Evaluate/type.cpp

@@ -580,4 +580,58 @@ int SelectedRealKind(
     }
   }
 }
+
+std::optional<DynamicType> ComparisonType(
+    const DynamicType &t1, const DynamicType &t2) {
+  switch (t1.category()) {
+  case TypeCategory::Integer:
+    switch (t2.category()) {
+    case TypeCategory::Integer:
+      return DynamicType{TypeCategory::Integer, std::max(t1.kind(), t2.kind())};
+    case TypeCategory::Real:
+    case TypeCategory::Complex:
+      return t2;
+    default:
+      return std::nullopt;
+    }
+  case TypeCategory::Real:
+    switch (t2.category()) {
+    case TypeCategory::Integer:
+      return t1;
+    case TypeCategory::Real:
+    case TypeCategory::Complex:
+      return DynamicType{t2.category(), std::max(t1.kind(), t2.kind())};
+    default:
+      return std::nullopt;
+    }
+  case TypeCategory::Complex:
+    switch (t2.category()) {
+    case TypeCategory::Integer:
+      return t1;
+    case TypeCategory::Real:
+    case TypeCategory::Complex:
+      return DynamicType{TypeCategory::Complex, std::max(t1.kind(), t2.kind())};
+    default:
+      return std::nullopt;
+    }
+  case TypeCategory::Character:
+    switch (t2.category()) {
+    case TypeCategory::Character:
+      return DynamicType{
+          TypeCategory::Character, std::max(t1.kind(), t2.kind())};
+    default:
+      return std::nullopt;
+    }
+  case TypeCategory::Logical:
+    switch (t2.category()) {
+    case TypeCategory::Logical:
+      return DynamicType{TypeCategory::Logical, LogicalResult::kind};
+    default:
+      return std::nullopt;
+    }
+  default:
+    return std::nullopt;
+  }
+}
+
 } // namespace Fortran::evaluate