[flang] Fix NAMELIST input bug with multiple subscript triplets

NAMELIST input can contain array subscripts with triplet notation.
The calculation of the default effective stride for the constructed
array descriptor was simply incorrect after the first dimension.

Differential Revision: https://reviews.llvm.org/D112347

Author: klausler

flang/runtime/namelist.cpp

@@ -10,6 +10,7 @@
 #include "descriptor-io.h"
 #include "io-stmt.h"
 #include "flang/Runtime/io-api.h"
+#include <algorithm>
 #include <cstring>
 #include <limits>
 
@@ -133,7 +134,7 @@ static bool HandleSubscripts(IoStatementState &io, Descriptor &desc,
   // ambiguous within the parentheses.
   SubscriptValue lower[maxRank], upper[maxRank], stride[maxRank];
   int j{0};
-  std::size_t elemLen{source.ElementBytes()};
+  std::size_t contiguousStride{source.ElementBytes()};
   bool ok{true};
   std::optional<char32_t> ch{io.GetNextNonBlank()};
   for (; ch && *ch != ')'; ++j) {
@@ -142,7 +143,9 @@ static bool HandleSubscripts(IoStatementState &io, Descriptor &desc,
       const Dimension &dim{source.GetDimension(j)};
       dimLower = dim.LowerBound();
       dimUpper = dim.UpperBound();
-      dimStride = elemLen ? dim.ByteStride() / elemLen : 1;
+      dimStride =
+          dim.ByteStride() / std::max<SubscriptValue>(contiguousStride, 1);
+      contiguousStride *= dim.Extent();
     } else if (ok) {
       handler.SignalError(
           "Too many subscripts for rank-%d NAMELIST group item '%s'",