How to define macros in a tablegen file?

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#1

Hi,

I was wondering if there is a way to specify macros to help shorten
rewriting patterns like these:

def : Pat <(v4i8 (mul (v4i8 IntRegs:$a), (v4i8 IntRegs:$b))),
  (v4i8
   (VTRUNEHB
    (v4i16
     (VTRUNEWH
      (v2i32
       (VMPYH
        (v2i16
         (EXTRACT_SUBREG (v4i16 (VSXTBH (v4i8 IntRegs:$a))), subreg_hireg)),
        (v2i16
         (EXTRACT_SUBREG (v4i16 (VSXTBH (v4i8 IntRegs:$b))), subreg_hireg)))),
      (v2i32
       (VMPYH
        (v2i16
         (EXTRACT_SUBREG (v4i16 (VSXTBH (v4i8 IntRegs:$a))), subreg_loreg)),
        (v2i16
         (EXTRACT_SUBREG (v4i16 (VSXTBH (v4i8 IntRegs:$b))), subreg_loreg)))))))
  )>;

Basically if we have a way to name a dag foo to be this:
(EXTRACT_SUBREG (v4i16 (VSXTBH $X)), $Y)

and bar to stand for this:
(v2i32 (VMPYH (v2i16 (foo $X, $Z)), (v2i16 (foo $Y, $Z))))

then, I could write the same pattern in a shorter format:
def : Pat <(v4i8 (mul (v4i8 IntRegs:$a), (v4i8 IntRegs:$b))),
  (v4i8
   (VTRUNEHB
    (v4i16
     (VTRUNEWH (bar IntRegs:$a, IntRegs:$b, subreg_hireg),
               (bar IntRegs:$a, IntRegs:$b, subreg_loreg)))))
  >;

Thanks,
Sebastian

#2

If the patterns only include SDNodes, then pattern fragments will work.

I might be wrong, but I've yet to find a way to do it with machine instructions, which is what you seem to have here.

Micah

#3

Hi Micah,

#4

For reference, here is how the SPU port is using code and pattern fragments:

// Holder of code fragments (you'd think this'd already be in
// a td file somewhere... :slight_smile:

class CodeFrag<dag frag> {
  dag Fragment = frag;
}

class I64SETCCNegCond<PatFrag cond, CodeFrag compare>:
  Pat<(cond R64C:$rA, R64C:$rB),
      (XORIr32 compare.Fragment, -1)>;

def : I64SETCCNegCond<setne, I64EQr64>;
def : I64SELECTNegCond<setne, I64EQr64>;

Sebastian

#5

Interesting, I'll have to look into that. I have some pretty big pattern files I would love to refactor into simpler patterns.

Micah

#6

And this comment makes me think, shouldn't this class CodeFrag be
included in the same place where PatFrag is declared:

./include/llvm/Target/TargetSelectionDAG.td:544:class PatFrag<dag ops,
dag frag, code pred = [{}],

such that we get it included through "llvm/Target/Target.td"?

I will prepare a patch for this.

Sebastian

#7

Please see the attached patch. Ok to commit?

Thanks,
Sebastian

0001-move-CodeFrag-from-CellSPU-to-generic-code.patch (1.69 KB)

#8

Possible to add a test case?

Micah

#9

I am not really sure what I would check.

At first, I thought to add a testcase to test/TableGen; as this patch
does not modify tablegen, it doesn't make sense.

What kind of test should I write for this? The test should be a
tablegen file that includes "llvm/Target/TargetSelectionDAG.td" or
"llvm/Target/Target.td", and I haven't seen any of these in the
testsuite.

Sebastian

#10

Ok, I was thinking there might be a test similar to PatFrag that could be created, but I noticed there are no tests for PatFrag either.

So that patch looks fine to me.

Micah

#11

Sebastian,

If not a test, how about a patch in the documentation for TableGen about this new feature that you're making available?

#12

That's a good point. I will prepare a patch for the docs.

Thanks for your review!
Sebastian

#13

Make sure to pull from the repo because the TableGen docs have been moved from HTML to reStructuredText very, very recently; it would be unfortunate if you did your work on the now-nonexistent HTML version, only to find that that file no longer exists.

–Sean Silva

#14

Ok, thanks for the heads up: I haven't started yet.

Sebastian