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Re: [PATCH] Fix PR80776
- From: Jeff Law <law at redhat dot com>
- To: Richard Biener <rguenther at suse dot de>, gcc-patches at gcc dot gnu dot org
- Date: Mon, 27 Nov 2017 10:04:06 -0700
- Subject: Re: [PATCH] Fix PR80776
- Authentication-results: sourceware.org; auth=none
- References: <alpine.LSU.2.20.1711271436550.12252@zhemvz.fhfr.qr>
On 11/27/2017 06:39 AM, Richard Biener wrote:
>
> The following avoids -Wformat-overflow false positives by teaching
> EVRP the trick about __builtin_unreachable () "other" edges and
> attaching range info to SSA names. EVRP does a better job in keeping
> ranges for every SSA name from conditional info (VRP "optimizes" its
> costly ASSERT_EXPR insertion process).
>
> Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.
>
> This will also fix the testcase from PR83072 but it doesn't really
> fix all cases I want to fix with a fix for it. OTOH it might be
> this is enough for stage3.
>
> Richard.
>
> 2017-11-27 Richard Biener <rguenther@suse.de>
>
> PR tree-optimization/80776
> * gimple-ssa-evrp-analyze.h (evrp_range_analyzer::set_ssa_range_info):
> Declare.
> * gimple-ssa-evrp-analyze.c (evrp_range_analyzer::set_ssa_range_info):
> New function.
> (evrp_range_analyzer::record_ranges_from_incoming_edges):
> If the incoming edge is an effective fallthru because the other
> edge only reaches a __builtin_unreachable () then record ranges
> derived from the controlling condition in SSA info.
> (evrp_range_analyzer::record_ranges_from_phis): Use set_ssa_range_info.
> (evrp_range_analyzer::record_ranges_from_stmt): Likewise.
>
> * gcc.dg/pr80776-1.c: New testcase.
> * gcc.dg/pr80776-2.c: Likewise.
So the thing to make sure of here is that the range information we
reflect back into the SSA_NAME actually applies everywhere the SSA_NAME
can appear. ie, it's globally valid.
This means we can't reflect anything we derive from conditionals or
things like a *p making the range non-null back to the SSA_NAME.
I'd be concerned about the change to record_ranges_from_incoming_edge.
Jeff