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

[Dan]

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.

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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