compiler errors - Implied DO-loop compilation performance

Question

The following implied Do-loop produces a bad performance at compile time

haarWPhi2D = reshape([((((((2**(-j/2))*haarWaveletPhi((2**j)*(m*dx)-k))* &
 ((2**(-j/2))*haarWaveletPhi((2**j)*(n*dt)-l)), &
  m = -grid_size, grid_size), k = -grid_size, grid_size), &
   n = 0, num_time_steps), l = 0, num_time_steps)], shape(haarWPhi2D))

I don't understand why the compilation is extremely slow and depending of the value of the finals may even never finish the compilation. For example with some of them at 100.

I'm not an expert but I expect in any case the performance to be affected at run time not at compile time.

Compiler version: GCC version 9.3.0
 Compiler options: -mtune=generic -march=x86-64 -fpre-include=/usr/include/finclude/math-vector-fortran.h

--Update--

This is a simple case that can be used to prove the problem

program main

    implicit none
        integer :: m, n
        integer :: k = 0
        integer :: l = 0
        integer, parameter :: num_time_steps = 100
        integer, parameter :: grid_size = 100
        real :: haarWPhi2D(-grid_size:grid_size, -grid_size:grid_size, 0:num_time_steps, 0:num_time_steps)
        haarWPhi2D = reshape([((((1, &
            m = -grid_size, grid_size), k = -grid_size, grid_size), &
                n = 0, num_time_steps), l = 0, num_time_steps)], shape(haarWPhi2D))

end program main

question from:https://stackoverflow.com/questions/65877589/implied-do-loop-compilation-performance

Answer 1

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