[Bug ada/25900] [4.2 Regression] ICE on ACATS cxac004 in Tree-VRP

[law at redhat dot com]

------- Comment #8 from law at redhat dot com  2006-01-26 17:14 -------
Subject: Re:  [4.2 Regression] ACATS ICE cxac0004 in
        set_value_range, at tree-vrp.c:161 on x86-linux

On Tue, 2006-01-24 at 15:12 -0700, Jeffrey A Law wrote:
> That "fixes" cxac004, but causes c99004a to fail!
As Laurent noted, c99004a has been failing without rhyme or reason
and the failure is not an indication of a regression due to my patch.

So I'm going to go forward with my patch.

The basic problem is we query SCEV to get ranges in some cases and
we query it on a different type than we ultimately care about. And
I've been unable to convince myself that even if we passed it the
right type that SCEV would do the right thing.

This patch makes VRP check the result of querying SCEV against the
type we actually care about.  When SCEV's result is inconsistent with
the type we car about, we simply ignore SCEV's result.

This patch also refines my recent change in one case.  Specifically if
we are intersecting a VR_RANGE and VR_ANTI_RANGE where the VR_ANTI_RANGE
is completely contained within the VR_RANGE, we have the option of
using either the VR_RANGE or VR_ANTI_RANGE as the result.  We were
selecting the VR_ANTI_RANGE, but in practice the VR_RANGE is likely
going to be more precise.  So I've changed the code to give us the
VR_RANGE instead.

About the only time the VR_ANTI_RANGE might be more useful would be if
it was something like -[0, 0] and referred to a pointer type.  Note
that I'll be looking more closely at the VRP null-pointer check
elimination code shortly so if the need arises I may add that final
bit of refinement.

Anyway, bootstrapped and regression tested on i686-pc-linux-gnu
(ada included).

Jeff


------- Comment #9 from law at redhat dot com  2006-01-26 17:14 -------
Created an attachment (id=10735)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=10735&action=view)


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25900