[flang] Fix IsConstantExpr for division expressions

[jeanPerier]

Summary

Fortran::evaluate::IsConstantExpr did not check that the numerator
was a constant expression. This patch fixes the issue.

[klausler]

Thanks!

[PeteSteinfeld]

Looks good. Thanks for doing this.

flang/lib/Evaluate/check-expression.cpp

bool operator()(const Component &component) const {
     return (*this)(component.base());
   }
   // Forbid integer division by zero in constants.
   template <int KIND>
   bool operator()(
       const Divide<Type<TypeCategory::Integer, KIND>> &division) const {
     using T = Type<TypeCategory::Integer, KIND>;
     if (const auto divisor{GetScalarConstantValue<T>(division.right())}) {
-      return !divisor->IsZero();
+      return !divisor->IsZero() && (*this)(division.left());
     } else {
       return false;
     }
   }
 };
 
 template <typename A> bool IsConstantExpr(const A &x) {
   return IsConstantExprHelper{}(x);

flang/test/Semantics/resolve37.f90

 !ERROR: Must have INTEGER type, but is REAL(4)
 character(len=l) :: v
 !ERROR: Initialization expression for PARAMETER 'o' (o) cannot be computed as a constant value
 real, parameter ::  o = o
 !ERROR: Must be a constant value
 integer, parameter ::  p = 0/0
 !ERROR: Must be a constant value
 integer, parameter ::  q = 1+2*(1/0)
+integer not_constant
+!ERROR: Must be a constant value
+integer, parameter :: s1 = not_constant/2
+!ERROR: Must be a constant value
+integer, parameter :: s2 = 3/not_constant
 !ERROR: Must be a constant value
 integer(kind=2/0) r
 integer, parameter :: sok(*)=[1,2]/[1,2]
 !ERROR: Must be a constant value
 integer, parameter :: snok(*)=[1,2]/[1,0]
 end