*Ping* patch, fortran] Warn about constant integer divisions

[Harald Anlauf]

Steve,

I do not see any check on the remainder of the integer division.
A truncation warning is pointless for expressions like 4/2 or
n*(n+1)/2 with n an integer parameter.

I use similar expressions for static decompositions or blocking
that I am afraid would produce warnings in several places.
Just tell me what the option would be to turn the warning off.

After all, we're not quiche eaters. :)

Harald

On 06/23/15 23:00, Steve Kargl wrote:
> On Tue, Jun 23, 2015 at 08:45:35PM +0200, Harald Anlauf wrote:
>>
>> I would not be happy to get a warning for integer division with
>> -Wconversion, which is perfectly valid and normal code.
>>
>> Adding this feature to -Wconversion would make this flag unusable for me.
>>
>> If you searched for a more suitable flag, I'd recommend -Wsurprising.
>>
> 
> Have you actually read the patch and understand what it does?
> It is a compile time warning when constant-folding occurs.  It 
> is not a runtime error.  Do really have a large amount of code
> that initializes variables via integer division?
> 
> program a
>   integer i,j
>   real x
>   x = 3 / 5  ! warning.    Programming error? x = 0.666 or 0?
>   i = 3 / 5  ! no warning. fancy way to init i to 0?
>   i = 4
>   x = x / i  ! no warning
>   j = i / 3  ! no warning
>   i = 5/3    ! warning.    fancy way to init j to 1?
> end program a
> 
> For the record, when I was coding up a variable-order 
> runge-kutta algorithm, I actually made the mistake in
> one of 33 named constants of doing exactly what this
> warning is meant to catch.  That code now does 
> something along the lines of
> 
> real(knd), parameter :: b21 =  real(    1, knd) / 5      ! 1/5
> real(knd), parameter :: b31 =  real(    3, knd) / 40     ! 3/40
> real(knd), parameter :: b32 =  real(    9, knd) / 40     ! 9/40
> real(knd), parameter :: b41 =  real(    3, knd) / 10     ! 3/10
> real(knd), parameter :: b42 = -real(    9, knd) / 10     ! -9/10
> 
> Thomas, please following Janne's suggestion of adding a new
> -W option (I'll suggest -Winteger-division) and add this
> to -Wall.
>