[Bug tree-optimization/22184] tree vectorizer depends on context
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22184 Richard Guenther rguenth at gcc dot gnu.org changed: What|Removed |Added Blocks||53947 --- Comment #4 from Richard Guenther rguenth at gcc dot gnu.org 2012-07-13 08:36:08 UTC --- Link to vectorizer missed-optimization meta-bug.
[Bug tree-optimization/22184] tree vectorizer depends on context
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22184 Richard Guenther rguenth at gcc dot gnu.org changed: What|Removed |Added Status|NEW |RESOLVED Resolution||FIXED --- Comment #5 from Richard Guenther rguenth at gcc dot gnu.org 2012-07-13 14:02:17 UTC --- This is fixed, even if I disable VRP / jump-threading and substitute the info from comment #3 in the code: double MyFunc2 (int size) { int len = size + 1; double Data[16] = {0}; if (len 3) ; else if (len 0) ; else return 0; for (int i=0; ilen; i++) Data[i] = Data[i]=0 ? Data[i] : -Data[i]; return Data[1]; }
[Bug tree-optimization/22184] tree vectorizer depends on context
-- What|Removed |Added CC||spop at gcc dot gnu dot org Last reconfirmed|2005-07-07 07:47:46 |2005-09-24 16:25:06 date|| http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22184
[Bug tree-optimization/22184] tree vectorizer depends on context
--- Additional Comments From irar at il dot ibm dot com 2005-07-07 07:47 --- The problem occurs in decision whether the number of loop iterations is greater than zero. The (single) predecessor edge is checked for being EDGE_TRUE_VALUE or EDGE_FALSE_VALUE, and the corresponding predicate is used to make the decision. In the first case (single loop) BB 0 contains predicate 'len0', its TRUE successor is BB 1, and the fallthru successor of BB 1 is BB 2 - the loop. The condition to check is 'len = 0', which is therefore simplified to FALSE. In the second case, however, the control flow is more complicated. The loop is in BB 6, its predecessor is BB 3, which has 2 predecessors: BB 5 (with predicate 'len 0'), and BB 2 - the first loop. The first loop is also guarded by 'len 0', but this information is not propagated. -- What|Removed |Added CC||rakdver at atrey dot karlin ||dot mff dot cuni dot cz Last reconfirmed|2005-06-25 18:28:42 |2005-07-07 07:47:46 date|| http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22184
[Bug tree-optimization/22184] tree vectorizer depends on context
--- Additional Comments From rakdver at gcc dot gnu dot org 2005-07-07 10:52 --- More precisely, the code when it comes to loop optimizer looks basically as if (len 3) something; else if (len 0) something_else; else return; for (i = 0; i len; i++) whatever; So indeed, len 0 on each path that reaches the loop, but it is not trivial to deduce. One solution is to use the results of VRP here. However, VRP uses scev analysis, and adding yet another cycle into the current completely incomprehensible nest of dependences between # of iterations analysis and SCEV seems quite scary to me (and there are other technical difficulties with this solution -- running VRP twice is bad from efficiency reasons, but keeping results of VRP valid is not entirely trivial and may prevent some optimizations). The other possibility is to extend the current oracle-like approach (# of iterations analysis basically asks whether a given condition -- len 0 in this case -- is true, and answer is computed on-demand by traversing SSA and dominance tree) to handle also this case. This would however need to have the ASSERT_EXPRs (so we either would need to insert them before loop optimizer, or keep them valid since VRP, neither of which seems to be good for performance and memory consumption). -- What|Removed |Added CC||dnovillo at redhat dot com http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22184
[Bug tree-optimization/22184] tree vectorizer depends on context
--- Additional Comments From pinskia at gcc dot gnu dot org 2005-06-25 18:28 --- Confirmed, I think this is a bug in scaler evolution though. -- What|Removed |Added Severity|normal |enhancement Status|UNCONFIRMED |NEW Ever Confirmed||1 Keywords||missed-optimization Last reconfirmed|-00-00 00:00:00 |2005-06-25 18:28:42 date|| http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22184