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[Bug tree-optimization/81192] [8 Regression] gcc ICE at -Os on x86_64-linux-gnu: Segmentation fault
- From: "vries at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Fri, 30 Jun 2017 16:32:25 +0000
- Subject: [Bug tree-optimization/81192] [8 Regression] gcc ICE at -Os on x86_64-linux-gnu: Segmentation fault
- Auto-submitted: auto-generated
- References: <bug-81192-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81192
--- Comment #11 from Tom de Vries <vries at gcc dot gnu.org> ---
Created attachment 41658
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41658&action=edit
3 - Ignore EDGE_DFS_BACK in tail-merge
This is a fix for the issue noted in comment 7: EDGE_DFS_BACK is in an
undefined state during tail-merge, but taken into account when comparing edges,
which causes missed merge opportunities in tail-merge.
This patch fixes the issue by ignoring EDGE_DFS_BACK in tail-merge.
For the example in this PR, the patch allows us to merge two latch blocks in
the same loop. Previously this merge didn't happen because one bb had
EDGE_DFS_BACK set on the back-edge, while the other one did not.
A fix for trunk only, the previous two we probably want to back-port.