[PATCH] tree-optimization/103440 - Always track arguments, even when ignoring equiv params.

Richard Biener richard.guenther@gmail.com
Tue Nov 30 07:42:51 GMT 2021

On Mon, Nov 29, 2021 at 6:20 PM Andrew MacLeod via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
> I need to adjust the original patch, I shouldn't have continued the loop
> when dealing with equivalences.    An equivalence is not the same as an
> undefined value...  we might be able to ignore the range from it for
> calculation purposes, but we cannot ignore the fact that it is a
> different SSA_NAME and may contain a different value that we do care about.
> There are other checks in then loop which will allow us to assign an
> equivalence between the DEF and an argument if we are ignoring the other
> ssa_names..  such as when there are undefined values.
> a_3 = PHI <a_1(4), a_2(6)>
> if a_2 is undefined, we can create an equivalence between a_3 and a_1 as
> the value of a_2 is irrelevant and can be whatever we want it to be.
> if a_2 is instead an equivalence with a_3, we do not want to create an
> equivalence between a_3 and a_1 in this block as we may then turn it
> into a copy.. we'd only be able to do this if there was an equivalence
> between a_1 and a_2, and we are not checking that.
> Although we are may not be adding the range for a_2 into the cumulative
> knowledge of a_3's range, we do need to keep the edge to retain the copy
> as its value is important and could be different than the other
> argument... and we need to retain the copy when we go out of ssa.
> This fixes that oversight, bootstrapped on x86_64-pc-linux-gnu with no
> regressions.  OK?


> Caveat..  the test case has an infinite loop without this fix, but
> degagnu doesn't seem to kill it, and my test suite runs go forever.. if
> there something I am missing?   The gcc.log claims that it timeouts
> after 300 second, but it doesn't kill the executable. I set the
> dg-timeout field, but that appears to be a compile time timeout, not
> runtime anyway.

Might be an old issue with your dejagnu, it should work.


> Andrew

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