Messages in this thread | | | Date | Thu, 10 Jul 2003 09:39:18 -0700 | From | Richard Henderson <> | Subject | Re: [PATCH] Fix do_div() for all architectures |
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On Thu, Jul 10, 2003 at 06:18:59PM +0200, Andrea Arcangeli wrote: > On Thu, Jul 10, 2003 at 08:40:19AM -0700, Richard Henderson wrote: > > On Tue, Jul 08, 2003 at 08:27:26PM +0200, Bernardo Innocenti wrote: > > > +extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor) > > > __attribute_pure__; > > ... > > > + __rem = __div64_32(&(n), __base); \ > > > > The pure declaration is very incorrect. You're writing to N. > > now pure sounds more reasonable, I wondered how could gcc keep track of > the stuff pointed by the parameters (especially if this stuff points to > other stuff etc.. ;).
Bernardo mis-interpreted the documentation.
Define "local memory" as memory from the current stack frame.
Define "non-local memory" as anything else (including stack memory from another function, or a different instantiation of the current function).
Any function can read/write local memory (since that is not visible to anyone outside the function).
A "const" function cannot read or write to non-local memory. There are further constraints on not returning abnormally or not returning at all that I'll not go into now.
A "pure" function can read non-local memory, but cannot write to it.
We use those conditions to determine if two invocations of a function can be collapsed or moved or removed.
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