Re: [PATCH] Fix PR80776

[Jeff Law <law@redhat.com>]

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