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Re: [patch] for PR 17531


On Tue, Sep 28, 2004 at 02:44:33AM +0200, Zdenek Dvorak wrote:
> is it really necessary to use this tone?  I spent a second thinking and
> observed that if you were right, the optimization would either not work
> at all or consistently cause misscompilations on LP64 platforms.  Which
> it does not.

My guess is that the extra conversions increase the cost a bit,
which presumably arranges for us to not choose this variant.

Which is extra work that might be avoided, as well as actively
rather than accidentally avoiding generating incorrect code.

> for (p = &a; p < &a + 200B; p += 2B)
>   *p = (short) (p - &a);
> 
> is perfectly valid.

Sure, but 

   *p = (short)((short)p - (short) &a)

isn't.  So any time you find yourself truncating a pointer rather
than an integer you should fail the operation.



r~


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