Demikhovsky, Elena
2012-Feb-07 08:38 UTC
[LLVMdev] DAG optimization and lowering algorithm
At the beginning, I have the following chain: LOAD -> TRUNCATE -> ZERO_EXTEND. After Combine(BeforeLegalizeTypes) the optimization of ZERO_EXTEND gives me the new chain LOAD -> ANY_EXTEND -> AND. I want to optimize ANY_EXTEND but is not analyzed in the same Combine(). Combine(AfterLegalizeTypes) is no called at all. - Elena -----Original Message----- From: Eli Friedman [mailto:eli.friedman at gmail.com] Sent: Tuesday, February 07, 2012 10:15 To: Demikhovsky, Elena Cc: llvmdev at cs.uiuc.edu Subject: Re: [LLVMdev] DAG optimization and lowering algorithm On Mon, Feb 6, 2012 at 11:54 PM, Demikhovsky, Elena <elena.demikhovsky at intel.com> wrote:> Hi, > > I'm trying to build code for very short function and I encounter with a problem (or bug) in DAG selection algotithm. > I have a node that was created in Combine(BeforeLegalizeTypes) and should be optimized in Combine(AfterLegalizeTypes). But LegalizeTypes() did not change anything and Combine(AfterLegalizeTypes) was not called. > Vector legalization that comes afterwards just scalarized the operation. > > SelectionDAGISel::CodeGenAndEmitDAG() > .. > CurDAG->Combine(BeforeLegalizeTypes, *AA, OptLevel); > > bool Changed; > Changed = CurDAG->LegalizeTypes(); > > if (Changed) { > CurDAG->Combine(AfterLegalizeTypes, *AA, OptLevel); > } > > The problem does not exist if the function is bigger and something was changed on LegalizeTypes() stage. > > I think that Combine(AfterLegalizeTypes) should be called anyway, even if LegalizeTypes() did not change anything.We skip the extra run as a performance optimization... we really don't want extra runs of DAGCombine if we can avoid it. If there is some optimization that currently only runs after type legalization, perhaps we can change it? -Eli --------------------------------------------------------------------- Intel Israel (74) Limited This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies.
On Tue, Feb 7, 2012 at 12:38 AM, Demikhovsky, Elena <elena.demikhovsky at intel.com> wrote:> At the beginning, I have the following chain: LOAD -> TRUNCATE -> ZERO_EXTEND. > After Combine(BeforeLegalizeTypes) the optimization of ZERO_EXTEND gives me the new chain LOAD -> ANY_EXTEND -> AND. > > I want to optimize ANY_EXTEND but is not analyzed in the same Combine().That sounds like it's just a matter of making sure we don't forget to add the ANY_EXTEND to the worklist. We don't need a whole additional DAGCombine run for that. -Eli
Demikhovsky, Elena
2012-Feb-07 09:11 UTC
[LLVMdev] DAG optimization and lowering algorithm
One of possible solutions is running Combine() for full DAG cycle after cycle while anything is changed. And remember that if we plan to optimize something after type legalization and before operation legalization if (DCI.isBeforeLegalizeOps()) && !DCI.isBeforeLegalize()) { .. } The function may not be called at all. - Elena -----Original Message----- From: Eli Friedman [mailto:eli.friedman at gmail.com] Sent: Tuesday, February 07, 2012 10:58 To: Demikhovsky, Elena Cc: llvmdev at cs.uiuc.edu Subject: Re: [LLVMdev] DAG optimization and lowering algorithm On Tue, Feb 7, 2012 at 12:38 AM, Demikhovsky, Elena <elena.demikhovsky at intel.com> wrote:> At the beginning, I have the following chain: LOAD -> TRUNCATE -> ZERO_EXTEND. > After Combine(BeforeLegalizeTypes) the optimization of ZERO_EXTEND gives me the new chain LOAD -> ANY_EXTEND -> AND. > > I want to optimize ANY_EXTEND but is not analyzed in the same Combine().That sounds like it's just a matter of making sure we don't forget to add the ANY_EXTEND to the worklist. We don't need a whole additional DAGCombine run for that. -Eli --------------------------------------------------------------------- Intel Israel (74) Limited This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies.