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[Bug tree-optimization/51005] -ftree-tail-merge slows down compilation of 20001226-1.c
- 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: Mon, 07 Nov 2011 09:53:15 +0000
- Subject: [Bug tree-optimization/51005] -ftree-tail-merge slows down compilation of 20001226-1.c
- Auto-submitted: auto-generated
- References: <bug-51005-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51005
--- Comment #1 from vries at gcc dot gnu.org 2011-11-07 09:53:15 UTC ---
-ftree-tail-merge optimises about half of the basic blocks away:
...
$ egrep -c '^<bb.*:' 20001226-1.c.091t.crited
16385
$ egrep -c '^<bb.*:' 20001226-1.c.092t.pre
8195
...
but it does so with a slowdown of factor 3.5:
...
$ time gcc src/gcc/testsuite/gcc.c-torture/compile/20001226-1.c -S -O2
-fno-tree-tail-merge
real 0m34.691s
user 0m34.350s
sys 0m0.220s
$ time gcc src/gcc/testsuite/gcc.c-torture/compile/20001226-1.c -S -O2
-ftree-tail-merge
real 2m7.072s
user 2m6.220s
sys 0m0.190s
...