[Flang] Static initialization failure for CHARACTER type when `constant-expr` is impl-do

[DanielCChen]

Consider the following code

  PROGRAM InitExpCharOP
  IMPLICIT NONE

  INTEGER     :: I
  CHARACTER(10),  PARAMETER :: A(10)= '0123456789'

  CHARACTER(LEN=10, KIND=1)  :: C1(10)= [(REPEAT(A(I)(1:I),1) // REPEAT(A(I)(I+1:10), 1) , I=1,10)]

  END

Flang currently issues an error as:

./a3.f:7:41: error: Initialization expression for 'c1' ([(repeat(a(int(int(i,kind=4),kind=8))(1_8:int(int(i,kind=4),kind=8)),1_8)//repeat(a(int(int(i,kind=4),kind=8))(int(int(i,kind=4)+1_4,kind=8):10_8),1_8),INTEGER(8)::i=1_8,10_8,1_8)]) cannot be computed as a constant value
    CHARACTER(LEN=10, KIND=1)  :: C1(10)= [(REPEAT(A(I)(1:I),1) // REPEAT(A(I)(I+1:10), 1) , I=1,10)]
                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The code seems conforming to me.
All ifort, gfortran and XLF compiled it successfully.

[llvmbot]

@llvm/issue-subscribers-flang-frontend

Author: Daniel Chen (DanielCChen)

Consider the following code ``` PROGRAM InitExpCharOP IMPLICIT NONE

INTEGER :: I
CHARACTER(10), PARAMETER :: A(10)= '0123456789'

CHARACTER(LEN=10, KIND=1) :: C1(10)= [(REPEAT(A(I)(1:I),1) // REPEAT(A(I)(I+1:10), 1) , I=1,10)]

END

Flang currently issues an error as:

./a3.f:7:41: error: Initialization expression for 'c1' ([(repeat(a(int(int(i,kind=4),kind=8))(1_8:int(int(i,kind=4),kind=8)),1_8)//repeat(a(int(int(i,kind=4),kind=8))(int(int(i,kind=4)+1_4,kind=8):10_8),1_8),INTEGER(8)::i=1_8,10_8,1_8)]) cannot be computed as a constant value
CHARACTER(LEN=10, KIND=1) :: C1(10)= [(REPEAT(A(I)(1:I),1) // REPEAT(A(I)(I+1:10), 1) , I=1,10)]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The code seems conforming to me. 
All ifort, gfortran and XLF compiled it successfully.
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