[LLVMdev] Help with promotion/custom handling of MUL i32 and MUL i64

[Duncan Sands]

Hi Dan,

On 30/07/13 21:14, Dan wrote:
>
> I'll try to run through the scenario:
>
>
> 64-bit register type target (all registers have 64 bits).
>
> all 32-bits are getting promoted to 64-bit integers
>
> Problem:
>
> MUL on i32 is getting promoted to MUL on i64
>
> MUL on i64 is getting expanded to a library call in compiler-rt
>
>
> the problem is that MUL32 gets promoted and then converted into a subroutine
> call because it is now type i64, even though I want the MUL I32 to remain as an
> operation in the architecture.  MUL i32 would generate a 64-bit results from the
> lower 32-bit portions of 64-bit source operands.

I think you should register custom type promotion logic, see
LegalizeIntegerTypes.cpp, line 40.  When this gets passed a 32
bit multiplication, it should promote it to a 64 bit operation
using the target specific node that does your special multiplication.

Ciao, Duncan.

>
> In customize for the operations, I am trying to do something like:
>
> case ISD::MUL:
>          {
>           EVT OpVT = Op.getValueType();
>            if (OpVT == MVT::i64) {
>              RTLIB::Libcall LC = RTLIB::MUL_I64;
>              SDValue Dummy;
>              return ExpandLibCall(LC, Op, DAG, false, Dummy, *this);
>            }
>            else if (OpVT == MVT::i32){
>
>              ??? What to do here to not have issues with type i32
>            }
>          }
>
>
> I've gone a few directions on this.
>
> Defining the architecture type i32 leads to a lot of changes that I don't think
> is the most straightforward change.
>
> Would think there is a way to promote the MUL i32 types but still be able to
> "see" that as a MUL i32 somewhere down the lowering process.
>
> Are there suggestions on how to promote the type, but then be able to customize
> the original i64 to a call and the original mul i32 to an operation?
>
>
>
>
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