[FIRRTL] DPI type check should not check the reference type.

sequencer commented 6 days ago

Think about this case:

module A:
  wire a : UInt<64>
  wire b : UInt<256>[256]
  intrinsic(circt_dpi_call<functionName = "some_func", isClocked = 1>, clock, enable, a, b)
module B:
  wire a : UInt<64>
  wire b : UInt<128>[256]
  intrinsic(circt_dpi_call<functionName = "some_func", isClocked = 1>, clock, enable, a, b)

some_func in these two different module should be lowered to a same function, despite A.b and B.b has different types:

    extern void some_func(long long in_0, svBitVecVal* out_0);

However firtool will complain:

'firrtl.int.dpi.call' op DPI function "some_func" input types don't match

This is used to dedup DPI-C functions, e.g. DPI call from different AXI agents, but with different datawidth. The payload type in each might be different, but they can still dedup.

uenoku commented 6 days ago

Good question but unfortunately SV spec doesn't allow that. Verilator will cause a compile error (and VCS emits a warning that "it might incorrectly compile"). If you import DPI functions with a same function name, the input types must be exactly same in System Verlog level.

We need to define b as an open array in that case and it's not added yet :)

sequencer commented 6 days ago

That’s a sad story. I think I have to duplicate that now. Thanks for your answer!

llvm / circt

[FIRRTL] DPI type check should not check the reference type. #7227