[Bug fortran/53778] bad code (delivering NaN instead of proper result) with -foptimize-sibling-calls

[dominiq at lps dot ens.fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53778

--- Comment #4 from Dominique d'Humieres <dominiq at lps dot ens.fr> 2012-06-27 13:44:43 UTC ---
I have played a little with the attached test (I had to comment out 'use
textdata' and 'use lapack'. On x86_64-apple-darwin10, I do not get any NaN with
4.6.3, 4.7.1, or trunk with the default flag. However if I add
'-finit-real=snan -ffpe-trap=invalid,zero,overflow' to the flags, the line

 single q:   1.6614401858304297                            NaN                 
     NaN

(for '-finit-real=nan') is replaced with

Floating exception

So it seems likely that the code is using uninitialized variable(s) (not
detected by -Wuninitialized). Note that one property of NaN is that they
"propagate", i.e., they can be detected quite far away from the point where
they are generated.

It looks like the bug is in the code rather than in gfortran.