Re: [PATCH] Speedup path discovery in predicate::use_cannot_happen

[Aldy Hernandez <aldyh@redhat.com>]

On Tue, Aug 23, 2022 at 2:16 PM Richard Biener <rguenther@suse.de> wrote:
>
> The following reverts a hunk from r8-5789-g11ef0b22d68cd1 that
> made compute_control_dep_chain start from function entry rather
> than the immediate dominator of the source block of the edge with
> the undefined value on the PHI node.  Reverting at that point
> does not reveal any testsuite FAIL, in particular the added
> testcase still passes.  The following adjusts this to the other
> function that computes predicates that hold on the PHI incoming
> edges with undefined values, predicate::init_from_phi_def, which
> starts at the immediate dominator of the PHI.  That's much less
> likely to run into the CFG walking limit.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu.
>
> Aldy - you did this change, do you remember anything here?  In
> fact the whole thing that's now called predicate::use_cannot_happen
> seems to be redundant - the two testcases attributed to its history
> do not fail when that's disabled, nor did they fail when it was
> introduced.  In principle whats now called predicate::superset_of
> should cover this (but different implementation limits might apply).

OMG, I'm drawing a complete blank here.  I have no recollection of
this.  I'm tempted to say either my account was hacked or that old
code was all wrong ;-).

Sorry.
Aldy