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[Bug tree-optimization/42108] [4.4/4.5 Regression] 50% performance regression
- From: "matz at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 14 Dec 2009 16:58:36 -0000
- Subject: [Bug tree-optimization/42108] [4.4/4.5 Regression] 50% performance regression
- References: <bug-42108-9410@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #35 from matz at gcc dot gnu dot org 2009-12-14 16:58 -------
Exactly my thinking (growing SCCs -> slow, sorting SCCs -> difficult).
What I thought about the trapping problem is that in this situation we could
ignore the trap test. We start with this situation:
bb1:
goto bb2
bb2:
PHI<from bb1, from bbX> ; with bbX being dominated by bb1
a = b / c ; with b and c loop invariant
Now it's clear that inserting a computation b/c in bb1 does not ever introduce
additional traps, as there's no intervening statement that could stop
execution without us knowing (in PR38819 it's a call that does exit(0)).
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42108