llvm dev - Sep 2006 - [LLVMdev] using the constant pool during select

In ARM, constants that are too large to be used as immediate are
usually placed in a constant pool and loaded.

What I am trying to do is to have a select function that checks the if
a constant can be an immediate and, if it can't, produces a load:

---------------------------------------------------------------------------------------
     const Type *OpNTy =  MVT::getTypeForValueType(MVT::i32);
      Constant *C = ConstantUInt::get(OpNTy, t);
      int alignment = 2;
      SDOperand Addr = CurDAG->getTargetConstantPool(C, MVT::i32, alignment);
      Arg =  CurDAG->getLoad(MVT::i32, CurDAG->getEntryNode(), Addr,
                             CurDAG->getSrcValue(NULL));
----------------------------------------------------------------------------------------

This fails with the assert "This target-independent node should have
been selected". It is illegal to create a load during select?

Should I write a lowering function to do this before the select phase?

Thanks,
Rafael

If you look at AlphaISelDAGToDAG.cpp:244, it probably does what you
want.  If a constant is too big, it spills it to the constant pool,
else it passes it through to the auto-generated selector.

Andrew

On 9/20/06, Rafael Espíndola <rafael.espindola at gmail.com>
wrote:
> In ARM, constants that are too large to be used as immediate are
> usually placed in a constant pool and loaded.
>
> What I am trying to do is to have a select function that checks the if
> a constant can be an immediate and, if it can't, produces a load:
>
>
---------------------------------------------------------------------------------------
>      const Type *OpNTy =  MVT::getTypeForValueType(MVT::i32);
>       Constant *C = ConstantUInt::get(OpNTy, t);
>       int alignment = 2;
>       SDOperand Addr = CurDAG->getTargetConstantPool(C, MVT::i32,
alignment);
>       Arg =  CurDAG->getLoad(MVT::i32, CurDAG->getEntryNode(), Addr,
>                              CurDAG->getSrcValue(NULL));
>
----------------------------------------------------------------------------------------
>
> This fails with the assert "This target-independent node should have
> been selected". It is illegal to create a load during select?
>
> Should I write a lowering function to do this before the select phase?
>
> Thanks,
> Rafael
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