[LLVMdev] DAG optimization and lowering algorithm

[Demikhovsky, Elena]

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.


- Elena


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