------- Comment #8 from dberlin at gcc dot gnu dot org 2008-11-02 20:53 -------
Subject: Re: [4.4 Regression] excessive memory consumption - possible hang
On Sun, Nov 2, 2008 at 7:04 AM, rguenth at gcc dot gnu dot org
<[EMAIL PROTECTED]> wrote:
>
>
> ------- Comment #5 from rguenth at gcc dot gnu dot org 2008-11-02 12:04
> -------
> More reduced:
>
> typedef int Int32;
> void use_it(int);
> void FindAndReadSignature(int processedSize)
> {
> int numPrevBytes = 1;
> for (;;)
> {
> int numBytesInBuffer = numPrevBytes + processedSize;
> Int32 numTests = numBytesInBuffer - 1;
> use_it (numTests);
> numPrevBytes = numBytesInBuffer - numTests;
> }
> }
>
> to not oscillate we rely on numTests _not_ be varying. It happens to be
> with the typedef as we forget to strip useless conversions. Otherwise
> we oscillate numPrevBytes (loop entry vs. back edge) between 1 and varying.
>
> Which may hint at that the speedup brought up by Danny (not processing a
> use further if it got varying) is even a correctness thing...
Things should never go up the lattice :)
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37991
