[Bug tree-optimization/55124] [4.8 Regression] ICE in find_or_generate_expression, at tree-ssa-pre.c:2803

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55124

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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         AssignedTo|vries at gcc dot gnu.org    |rguenth at gcc dot gnu.org

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> 2012-11-29 14:35:08 UTC ---
To summarize here, the issue is that PRE insertion (and also expression
clean and dependent_clean, but not really phi-translation) need to process
expression set from leafs (where the dependence tree is formed by the
value-ids of the expressions).  In ancient times this might have been
ensured by sorting expressions after their value-id
(sorted_array_from_bitmap_set), but at least with SCCVN there is no such
thing as a topological value-id assignment.

Thus, the correct fix is indeed to properly sort the expression array
according to expression dependencies.  Which then allows to get rid of
value-ids in SCCVN and compute them lazily in get_expr_value_id.

I'll take over from Tom here again.