Re: Possible ANSI C Optimisation Done in Practice?

I said:
> An ANSI C compiler does know the semantics of strlen if the compiler
> writers have arranged for that to be the case. For instance, AIX's
> <string.h> #defines strlen to be __strlen which the compiler
> recognises as *the* standard strlen function.


Something I just found: Robert Morgan in _Building an Optimizing
Compiler_ says on page 25


        Library routines are handled differently than other procedure
        calls. If a library procedure is known to be a pure function it is
        handled as if it were an operator. This allows the use of
        identities involving the library routines. Other procedure calls
        may be used in other parts of the analysis of the program, for
        example, calls on malloc are known to return either a null pointer
        or a pointer to a section of memory unreferenced in other parts of
        the program.


strlen(s) is pure. So that just leaves determining modifying *t
doesn't touch s.


Ralph.

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