[Bug tree-optimization/51005] -ftree-tail-merge slows down compilation of 20001226-1.c

[vries at gcc dot gnu.org]

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
...