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Re: GCC 4.8.0 Status Report (2012-10-29), Stage 1 to end soon


On Wed, Oct 31, 2012 at 09:44:50AM -0400, Kenneth Zadeck wrote:
> The tree-vpn uses an infinite-precision view of arithmetic. However,
> that infinite precision is implemented on top of a finite, CARVED IN
> STONE, base that is and will always be without a patch like this,
> 128 bits on an x86-64.    However, as was pointed out by earlier,
> tree-vrp needs 2 * the size of a type + 1 bit to work correctly.
> Until yesterday i did not fully understand the significance of that
> 1 bit.  what this means is that tree-vrp does not work on an x86-64
> with _int128 variables.

If you see a VRP bug, please file a PR with a testcase, or point to existing
PR.  I agree with richi that it would be better to add a clean wide_int
implementation for 4.9, rather than rushing something in, introducing
lots of bugs, just for a port that hasn't been submitted, nor I understand
why > int128_t integer types are so crucial to your port, the vector
support doesn't generally need very large integers, even if your
vector unit is 256-bit, 512-bit or larger.

	Jakub


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