[Bug tree-optimization/21982] GCC should combine adjacent stdio calls

[joseph at codesourcery dot com]

------- Additional Comments From joseph at codesourcery dot com  2005-06-09 14:36 -------
Subject: Re:  GCC should combine adjacent stdio
 calls

Another problem case is if the first format has excess arguments (which is 
permitted by ISO C) - those arguments must be evaluated but not included 
in the concatenated argument list.

Even if arguments don't have side effects you have problems if arguments 
of the second printf might refer to anything modifed by printf (the FILE 
structure, its buffers, the contents of the file written to, ...) - they 
should have the appropriate values for after the first call.  It's OK if 
the arguments are e.g. local integer variables whose addresses have not 
escaped, but in general you need to prove that the arguments to the second 
printf, and anything they point to, cannot be changed by the first printf.



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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21982