[flang] Diagnose REPEAT with negative NCOPIES=

[klausler]

Summary

Emit an error when the NCOPIES= argument to the intrinsic function
REPEAT has a negative value. (The current implementation crashes, which
isn't informative.)

[tschuett]

You tend to upload without context. Do you need a pointer for some help?

flang/lib/Evaluate/character.h

for (; j >= 1; --j) {
         break;
       }
     }
     return static_cast<ConstantSubscript>(j);
   }
 
   static Character REPEAT(const Character &str, ConstantSubscript ncopies) {
     Character result;
-    if (!str.empty()) {
+    if (!str.empty() && ncopies > 0) {
       result.reserve(ncopies * str.size());
       while (ncopies-- > 0) {
         result += str;
       }
     }
     return result;
   }
 

flang/lib/Evaluate/fold-character.cpp

if (name == "achar" || name == "char") {
     }
   } else if (name == "new_line") {
     return Expr<T>{Constant<T>{CharacterUtils<KIND>::NEW_LINE()}};
   } else if (name == "repeat") { // not elemental
     if (auto scalars{GetScalarConstantArguments<T, SubscriptInteger>(
             context, funcRef.arguments())}) {
       auto str{std::get<Scalar<T>>(*scalars)};
       auto n{std::get<Scalar<SubscriptInteger>>(*scalars).ToInt64()};
-      if (static_cast<double>(n) * str.size() >
+      if (n < 0) {
+        context.messages().Say(
+            "NCOPIES= argument to REPEAT() should be nonnegative, but is %jd"_err_en_US,
+            static_cast<std::intmax_t>(n));
+      } else if (static_cast<double>(n) * str.size() >
           (1 << 20)) { // sanity limit of 1MiB
         context.messages().Say(
             "Result of REPEAT() is too large to compute at compilation time (%g characters)"_port_en_US,
             static_cast<double>(n) * str.size());
       } else {
         return Expr<T>{Constant<T>{CharacterUtils<KIND>::REPEAT(str, n)}};
       }
     }

flang/test/Evaluate/errors01.f90

subroutine s12(x,y)
     !CHERK: error: Must be a constant value
     integer, parameter :: bad1 = storage_size(x)
     !CHERK: error: Must be a constant value
     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 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
     real, parameter :: bad3 = dim(huge(1.),-.5*huge(1.))
     !CHECK: warning: DIM intrinsic folding overflow
     integer, parameter :: bad4 = dim(huge(1),-1)
     !CHECK: warning: overflow on REAL(8) to REAL(4) conversion
     x = 1.D40
   end subroutine
 end module