[flang] Check constant POS/LEN arguments IBITS even when not both constant

[klausler]

Summary

Apply compile-time checks to the values supplied for the POS and LEN
arguments of the IBITS intrinsic function even when only one of them
is a known constant.

[PeteSteinfeld]

All builds and tests correctly and looks good.

flang/lib/Evaluate/fold-integer.cpp

return FoldElementalIntrinsic<T, T, Int4>(context, std::move(funcRef),
             [&](const Scalar<T> &i, const Scalar<Int4> &pos) -> Scalar<T> {
               return std::invoke(fptr, i, static_cast<int>(pos.ToInt64()));
             }));
   } else if (name == "ibits") {
     const auto *posCon{Folder<Int4>(context).Folding(args[1])};
     const auto *lenCon{Folder<Int4>(context).Folding(args[2])};
     if (const auto *argCon{Folder<T>(context).Folding(args[0])};
         argCon && argCon->empty()) {
-    } else if (posCon && lenCon &&
-        (posCon->size() == 1 || lenCon->size() == 1 ||
-            posCon->size() == lenCon->size())) {
-      auto posIter{posCon->values().begin()};
-      auto lenIter{lenCon->values().begin()};
-      for (; posIter != posCon->values().end() &&
-           lenIter != lenCon->values().end();
-           ++posIter, ++lenIter) {
-        posIter = posIter == posCon->values().end() ? posCon->values().begin()
-                                                    : posIter;
-        lenIter = lenIter == lenCon->values().end() ? lenCon->values().begin()
-                                                    : lenIter;
-        auto posVal{static_cast<int>(posIter->ToInt64())};
-        auto lenVal{static_cast<int>(lenIter->ToInt64())};
+    } else {
+      std::size_t posCt{posCon ? posCon->size() : 0};
+      std::size_t lenCt{lenCon ? lenCon->size() : 0};
+      std::size_t n{std::max(posCt, lenCt)};
+      for (std::size_t j{0}; j < n; ++j) {
+        int posVal{j < posCt || posCt == 1
+                ? static_cast<int>(posCon->values()[j % posCt].ToInt64())
+                : 0};
+        int lenVal{j < lenCt || lenCt == 1
+                ? static_cast<int>(lenCon->values()[j % lenCt].ToInt64())
+                : 0};
         if (posVal < 0) {
           context.messages().Say(
-              "bit position for IBITS(POS=%jd,LEN=%jd) is negative"_err_en_US,
-              std::intmax_t{posVal}, std::intmax_t{lenVal});
+              "bit position for IBITS(POS=%jd) is negative"_err_en_US,
+              std::intmax_t{posVal});
           break;
         } else if (lenVal < 0) {
           context.messages().Say(
-              "bit length for IBITS(POS=%jd,LEN=%jd) is negative"_err_en_US,
-              std::intmax_t{posVal}, std::intmax_t{lenVal});
+              "bit length for IBITS(LEN=%jd) is negative"_err_en_US,
+              std::intmax_t{lenVal});
           break;
         } else if (posVal + lenVal > T::Scalar::bits) {
           context.messages().Say(
-              "IBITS(POS=%jd,LEN=%jd) must have POS+LEN no greater than %d"_err_en_US,
-              std::intmax_t{posVal}, std::intmax_t{lenVal}, T::Scalar::bits);
+              "IBITS() must have POS+LEN (>=%jd) no greater than %d"_err_en_US,
+              std::intmax_t{posVal + lenVal}, T::Scalar::bits);
           break;
         }
       }
     }
     return FoldElementalIntrinsic<T, T, Int4, Int4>(context, std::move(funcRef),
         ScalarFunc<T, T, Int4, Int4>(
             [&](const Scalar<T> &i, const Scalar<Int4> &pos,
                 const Scalar<Int4> &len) -> Scalar<T> {

flang/test/Evaluate/errors01.f90

subroutine s12(x,y)
     integer, parameter :: bad2 = storage_size(y)
   end subroutine
   subroutine s13
     !CHECK: portability: Result of REPEAT() is too large to compute at compilation time (1.1259e+15 characters)
     print *, repeat(repeat(' ', 2**20), 2**30)
     !CHECK: error: NCOPIES= argument to REPEAT() should be nonnegative, but is -666
     print *, repeat(' ', -666)
   end subroutine
+  subroutine s14(n)
+    integer, intent(in) :: n
+    !CHECK: error: bit position for IBITS(POS=-1) is negative
+    print *, ibits(0, -1, n)
+    !CHECK: error: bit length for IBITS(LEN=-1) is negative
+    print *, ibits(0, n, -1)
+    !CHECK: error: IBITS() must have POS+LEN (>=33) no greater than 32
+    print *, ibits(0, n, 33)
+    !CHECK: error: IBITS() must have POS+LEN (>=33) no greater than 32
+    print *, ibits(0, 33, n)
+  end
   subroutine warnings
     real, parameter :: ok1 = scale(0.0, 99999) ! 0.0
     real, parameter :: ok2 = scale(1.0, -99999) ! 0.0
     !CHECK: SCALE intrinsic folding overflow
     real, parameter :: bad1 = scale(1.0, 99999)
     !CHECK: complex ABS intrinsic folding overflow
     real, parameter :: bad2 = abs(cmplx(huge(0.),huge(0.)))
     !CHECK: warning: DIM intrinsic folding overflow