[flang] Correct folding of TRANSFER(integer, character array)

[klausler]

Summary

The code that copies data from a constant source array into a character
array constant result was failing to copy its last element if it was
only partially defined due to misalignment.

[PeteSteinfeld]

All builds and tests correctly and looks good.

flang/lib/Evaluate/initial-image.cpp

       for (std::size_t j{0}; j < elements; ++j) {
         using Char = typename Scalar::value_type;
         auto at{static_cast<std::size_t>(offset_ + j * stride)};
-        if (at + length > image_.data_.size()) {
+        auto chunk{length};
+        if (at + chunk > image_.data_.size()) {
           CHECK(padWithZero_);
-          break;
+          if (at >= image_.data_.size()) {
+            chunk = 0;
+          } else {
+            chunk = image_.data_.size() - at;
+          }
+        }
+        if (chunk > 0) {
+          const Char *data{reinterpret_cast<const Char *>(&image_.data_[at])};
+          typedValue[j].assign(data, chunk);
+        }
+        if (chunk < length && padWithZero_) {
+          typedValue[j].append(length - chunk, Char{});
         }
-        const Char *data{reinterpret_cast<const Char *>(&image_.data_[at])};
-        typedValue[j].assign(data, length);
       }
       return AsGenericExpr(
           Const{length, std::move(typedValue), std::move(extents_)});

         if (at + chunk > image_.data_.size()) {
           CHECK(padWithZero_);
           if (at >= image_.data_.size()) {
-            break;
+            chunk = 0;
+          } else {
+            chunk = image_.data_.size() - at;
           }
-          chunk = image_.data_.size() - at;
         }
         // TODO endianness
-        std::memcpy(&typedValue[j], &image_.data_[at], chunk);
+        if (chunk > 0) {
+          std::memcpy(&typedValue[j], &image_.data_[at], chunk);
+        }
       }
       return AsGenericExpr(Const{std::move(typedValue), std::move(extents_)});
     }

flang/test/Evaluate/fold-transfer.f90

   logical, parameter :: test_c2i_v_2 = all(jc3 == [int(z'61626364'), int(z'65666768')]) .or. all(jc3 == [int(z'64636261'), int(z'68676665')])
   integer, parameter :: jc4(*) = transfer(["abcd", "efgh"], 0, 1)
   logical, parameter :: test_c2i_vs_1 = all(jc4 == [int(z'61626364')]) .or. all(jc4 == [int(z'64636261')])
+
+  integer, parameter :: le1 = int(z'64636261', 4), be1 = int(z'65666768', 4)
+  character*5, parameter :: le1c(*) = transfer(le1, [character(5)::])
+  character*5, parameter :: be1c(*) = transfer(be1, [character(5)::])
+  logical, parameter :: test_i2c_s = all(le1c == ["abcd"//char(0)]) .or. all(be1c == ["efgh"//char(0)])
 end module