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Strange effect of unused subroutines on results

 
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mecej4



Joined: 31 Oct 2006
Posts: 1895

PostPosted: Fri Dec 02, 2022 5:59 pm    Post subject: Strange effect of unused subroutines on results Reply with quote

I have a problem reproducer code that is about 220 lines long, of which about 70 lines are surrounded by #ifdef BIG ... #endif. These 70 lines contain two subroutines, neither of which is called from anywhere in the program. Nevertheless, including these lines in the compilation by defining BIG=1 causes the output of the program to change.

The source code may be downloaded from the cloud, using the link https://drive.google.com/file/d/1FwlLhhaqpb4X7ZmAU87GLhO6xeEgnisT/view?usp=sharing .

Compile and link and run using the command
Code:
ftn95 /Cfp /64 /check /define BIG 1 tmdcs.f90 /link

Running the program gives the output
Code:
mark(5), mark(8) =       5    8

which is wrong. The correct output is
Code:
mark(5), mark(8) =       2    2

as can be seen using other compilers (or by using FTN95 8.92 without /define BIG).

What is perplexing to me is that the inclusion of a subroutine that is never called and in which the only executable statement is RETURN can cause the calculated results to be affected.
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Robert



Joined: 29 Nov 2006
Posts: 449
Location: Manchester

PostPosted: Fri Dec 02, 2022 6:23 pm    Post subject: Reply with quote

That is odd. It seems related to the equivalence statement in mdu.
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mecej4



Joined: 31 Oct 2006
Posts: 1895

PostPosted: Fri Dec 02, 2022 6:44 pm    Post subject: Reply with quote

Indeed, Robert, the equivalence statement makes itself felt, even though the two variables being equivalenced are both local variables in a subroutine that is not called.

Similarly, I observed that if I removed some comment lines with PRINT statements in them the output of the program changed! Death to determinism?
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PaulLaidler
Site Admin


Joined: 21 Feb 2005
Posts: 7943
Location: Salford, UK

PostPosted: Sat Dec 03, 2022 9:39 am    Post subject: Reply with quote

The failure appears to be confined to /64 /check and a temporary work-around is to use /inhibit_check 10.
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PaulLaidler
Site Admin


Joined: 21 Feb 2005
Posts: 7943
Location: Salford, UK

PostPosted: Mon Jan 30, 2023 1:16 pm    Post subject: Reply with quote

This failure has been fixed for the next release of FTN95. It relates to 64 bits, CHECK mode and the use of EQUIVALANCE within subroutines in a CONTAINS section.
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