[Bug rtl-optimization/34826] New: branch probability is not reserved with do-loop optimization

[Bug rtl-optimization/34826] New: branch probability is not reserved with do-loop optimization

[eres at il dot ibm dot com]

Running the attached testcase with trunk r131577 on SPU
with -dm -fmodulo-sched -O2 flags (which enables also do-loop optimization)
demonstartes the fact that the branch probability is not reserved with do-loop
optimization.
This causes a major preformance regression (of about 40%) when tested with some
similar benchmark as there is no hardware branch prediction on SPU.


-- 
           Summary: branch probability is not reserved with do-loop
                    optimization
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: eres at il dot ibm dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34826

[Bug rtl-optimization/34826] branch probability is not reserved with do-loop optimization

[eres at il dot ibm dot com]

------- Comment #1 from eres at il dot ibm dot com  2008-01-17 07:21 -------
Created an attachment (id=14955)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=14955&action=view)
The testcase


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34826

[Bug rtl-optimization/34826] branch probability is not reserved with do-loop optimization

[steven at gcc dot gnu dot org]

------- Comment #2 from steven at gcc dot gnu dot org  2008-01-17 07:31 -------
Can you show in an RTL dump why you are sure that the branch probabilities are
lost?


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steven at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rakdver at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34826

[Bug rtl-optimization/34826] branch probability is not updated with do-loop optimization

[eres at il dot ibm dot com]

------- Comment #3 from eres at il dot ibm dot com  2008-01-17 08:17 -------
(In reply to comment #2)
> Can you show in an RTL dump why you are sure that the branch probabilities are
> lost?

Sure, I am currently testing a patch we have to fix this problem,
the following '-' lines are from the SMS dump generated with current trunk and
the '+' lines are generated from trunk containing the fix.

@@ -1955,7 +1955,7 @@
         (if_then_else (ne:SI (reg:SI 204 [ n ])
                 (const_int 0 [0x0]))
             (label_ref:SI 145)
-            (pc))) 356 {*spu.md:3450} (expr_list:REG_BR_PROB (const_int 5000
[0x1388])
+            (pc))) 356 {*spu.md:3450} (expr_list:REG_BR_PROB (const_int 9100
[0x238c])
         (nil)))
 ;; End of basic block 8 -> ( 10 9)
 ;; lr  out      1 [$sp] 127 [$127] 128 [$vfp] 129 [$vap] 176 177 178 179 180
181 183 201 204
@@ -2015,8 +2015,8 @@
 ;;      reg 204 { d110(bb 8 insn 104) }


-;; Succ edge  10 [50.0%]  (dfs_back)
-;; Succ edge  9 [50.0%]  (fallthru,loop_exit)
+;; Succ edge  10 [91.0%]  (dfs_back)
+;; Succ edge  9 [9.0%]  (fallthru,loop_exit)


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eres at il dot ibm dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|branch probability is not   |branch probability is not
                   |reserved with do-loop       |updated with do-loop
                   |optimization                |optimization


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34826

[Bug rtl-optimization/34826] branch probability is not updated with do-loop optimization

[eres at il dot ibm dot com]

------- Comment #4 from eres at il dot ibm dot com  2008-01-17 18:28 -------
A patch was committed to trunk -r131604


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34826

[Bug rtl-optimization/34826] branch probability is not updated with do-loop optimization

[pinskia at gcc dot gnu dot org]

------- Comment #5 from pinskia at gcc dot gnu dot org  2008-01-20 04:52 -------
Fixed.


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pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34826