[LLVMdev] Vector DAG Patterns

[Micah Villmow]

Does your target support v16i8 natively?  If not, then the DAG framework will split it up into the largest type your target supports.
Why are you attempting to do this in tablegen? This is something that should be trivially done in C++ code.
For example:
SDValue dst = DAG.getNode() <-- extract element 0
for (1 to vec size-1) {
  SDValue tmp = DAG.getNode() <-- extract element N
  dst = DAG.getNode(ISD::AND, DL, MVT::i8, dst, tmp);
}
return dst

Simple 5-6 line helper function does what looks to be a very complex and error prone tablegen pattern.

From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of Conor Mac Aoidh
Sent: Friday, July 26, 2013 3:28 AM
To: llvmdev at cs.uiuc.edu
Subject: Re: [LLVMdev] Vector DAG Patterns

To elaborate, it is not only cumbersome writing these patterns for vectors of 16 characters (v16i8), it does not work.

When I compile with this pattern for an andx operation on v16i8:

[(set RC:$dst,
  (and (i8 (vector_extract(vt VC:$src), 0 ) ),
    (and (i8 (vector_extract(vt VC:$src), 1 ) ),
        (and (i8 (vector_extract(vt VC:$src), 2 ) ),
            (and (i8 (vector_extract(vt VC:$src), 3 ) ),
              (and (i8 (vector_extract(vt VC:$src), 4 ) ),
                (and (i8 (vector_extract(vt VC:$src), 5 ) ),
                  (and (i8 (vector_extract(vt VC:$src), 6 ) ),
                    (and (i8 (vector_extract(vt VC:$src), 7 ) ),
                      (and (i8 (vector_extract(vt VC:$src), 8 ) ),
                         (and (i8 (vector_extract(vt VC:$src), 9 ) ),
                            (and (i8 (vector_extract(vt VC:$src), 10 ) ),
                                (and (i8 (vector_extract(vt VC:$src), 11 ) ),
                                  (and (i8 (vector_extract(vt VC:$src), 12 ) ),
                                    (and (i8 (vector_extract(vt VC:$src), 13 ) ),
                                      (and (i8 (vector_extract(vt VC:$src), 14 ) ),
                                        (i8 (vector_extract(vt VC:$src), 15 ) )
                                      )
                                    )
                                 )
                            )
                        )
                     )
                  )
                )
              )
            )
          )
        )
      )
    )
  )
)]

llvm-tblgen enters an infinite loop which never stops (i left it for ~10 mins before killing)

So either there is another way to express this pattern, or this is a problem with tablegen?

Regards
---
Conor Mac Aoidh

On 23/07/2013 12:03, Conor Mac Aoidh wrote:
Hi All,

Been having a problem constructing a suitable pattern to represent some vector operations in the DAG. Stuff like andx/orx operations where elements of a vector are anded/ored together.

My approach thus far has been to extract the sub elements of the vector and and/or those elements. This is ok for 4 vectors of i32s, but becomes cumbersome for v16i8s. Example instruction:

andx $dst $v1

Pattern:

[(set RC:$dst,
   (and (i32 (vector_extract(vt VC:$src), 0 ) ),
       (and (i32 (vector_extract(vt VC:$src), 1 ) ),
           (and (i32 (vector_extract(vt VC:$src), 2 ) ),
                (i32 (vector_extract(vt VC:$src), 3 ) )
           )
       )
    )
)]

Is there a better way to do this?

Regards
---
Conor Mac Aoidh

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