[Bug tree-optimization/17863] [4.0/4.1 Regression] threefold performance loss, not inlining as much

[steven at gcc dot gnu dot org]

------- Additional Comments From steven at gcc dot gnu dot org  2005-06-27 06:38 -------
As you can see from those numbers Dan Kegel posted, this kind of test case 
is very sensitive to the intermediate representation presented to the inliner 
and to inliner heuristics.  Personally, I don't think it is worth keeping a 
bug report like this opened.  This kind of almost-random behavior is similar 
to the reload failures on x86: You'll always be able to construct a test case 
that will fail with a "fixed" compiler for one particular case. 
 
However, in this case there are still a number of things that are interesting 
to look at: 
1) GCC 4.1 has profile guided inlining.  Does it help in this case? 
2) Does the early inlining patch [1] help? 
3) Does the pre-inlining patch and the IPA stuff help? (i.e. try the 
   tree-profiling-branch with all pistons firing ;-) 
 
Personally, I expect that this is a case where the pre-inline optimizations 
may be helpful 
 
Could someone construct a graphical representation of the call graphs for 
GCC 3.4 and GCC 4.1 and compare them?  I'm very curious which function (or 
functions) are apparently inlined only by GCC 3.4 and not by any other 
release. 
   
 
[1] http://gcc.gnu.org/ml/gcc-patches/2005-06/msg01839.html 
 

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17863