| Message ID | CAO2gOZWwv_UiVyr8FU8zeTJrk+CfTXPhtsT9eOpzbP4z-XUrQA@mail.gmail.com |
|---|---|
| State | New |
| Headers | show |
On Tue, Jul 31, 2012 at 5:17 AM, Dehao Chen <dehao@google.com> wrote: > Hi, > > This patch fixed the problem when a LOOP_EXIT edge for the inner loop > happened to target at the LOOP_LATCH of the outer loop. As the outer > loop is processed first, the LOOP_BRANCH heuristic is honored > (first_match), thus the inner loop's trip count is 0. (The attached > unittest demonstrates this). > > Bootstrapped and passed gcc regression test. > > Is it ok for trunk? > > Thanks, > Dehao > > gcc/ChangeLog > > 2012-07-30 Dehao Chen <dehao@google.com> > > * predict.c (predict_loops): Fix the prediction of LOOP_BRANCH. > > gcc/testsuite/ChangeLog > > 2012-07-31 Dehao Chen <dehao@google.com> > > * gcc.dg/predict-7.c: New test. > > Index: gcc/testsuite/gcc.dg/predict-7.c > =================================================================== > --- gcc/testsuite/gcc.dg/predict-7.c (revision 0) > +++ gcc/testsuite/gcc.dg/predict-7.c (revision 0) > @@ -0,0 +1,17 @@ > +/* { dg-do compile } */ > +/* { dg-options "-O2 -fdump-tree-profile_estimate" } */ > + > +extern int global; > + > +int bar (int); > + > +void foo (int base) > +{ > + int i; > + while (global < 10) > + for (i = base; i < 10; i++) > + bar (i); > +} > + > +/* { dg-final { scan-tree-dump-times "loop branch heuristics" 0 > "profile_estimate"} } */ > +/* { dg-final { cleanup-tree-dump "profile_estimate" } } */ > Index: gcc/predict.c > =================================================================== > --- gcc/predict.c (revision 189835) > +++ gcc/predict.c (working copy) > @@ -1404,7 +1404,7 @@ > > /* Loop branch heuristics - predict an edge back to a > loop's head as taken. */ > - if (bb == loop->latch) > + if (bb == loop->latch && bb->loop_father == loop) > { > e = find_edge (loop->latch, loop->header); > if (e) I think this heuristic should instead move out of the loop iterating over loop nodes and be done before like if (loop->latch) { e = find_edge (loop->latch, loop->header); ... } which also makes header_found initialized before we visit loop blocks. Instead the code /* Loop exit heuristics - predict an edge exiting the loop if the conditional has no loop header successors as not taken. */ if (!header_found /* If we already used more reliable loop exit predictors, do not bother with PRED_LOOP_EXIT. */ ... FOR_EACH_EDGE (e, ei, bb->succs) if (e->dest->index < NUM_FIXED_BLOCKS || !flow_bb_inside_loop_p (loop, e->dest)) predict_edge (e, PRED_LOOP_EXIT, probability); looks wrong for bb's that are parts of an inner loop of loop - assuming we only want to predicate exits from loop and not exits from an inner loop that also happen to exit loop (we will do that when predicating the inner loop). Is that what you experienced? Thanks, Richard.
Index: gcc/testsuite/gcc.dg/predict-7.c =================================================================== --- gcc/testsuite/gcc.dg/predict-7.c (revision 0) +++ gcc/testsuite/gcc.dg/predict-7.c (revision 0) @@ -0,0 +1,17 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fdump-tree-profile_estimate" } */ + +extern int global; + +int bar (int); + +void foo (int base) +{ + int i; + while (global < 10) + for (i = base; i < 10; i++) + bar (i); +} + +/* { dg-final { scan-tree-dump-times "loop branch heuristics" 0 "profile_estimate"} } */ +/* { dg-final { cleanup-tree-dump "profile_estimate" } } */ Index: gcc/predict.c =================================================================== --- gcc/predict.c (revision 189835) +++ gcc/predict.c (working copy) @@ -1404,7 +1404,7 @@ /* Loop branch heuristics - predict an edge back to a loop's head as taken. */ - if (bb == loop->latch) + if (bb == loop->latch && bb->loop_father == loop) { e = find_edge (loop->latch, loop->header); if (e)