[llvm-dev] dumb question about tblgen

Thu May 26 10:59:06 PDT 2016

Craig,
            I would humbly ask that “Target.td” be edited to include a commented out include of ValueTypes.td (just ahead of the include of Intrinsics.td) with an appropriate comment in the include line so that you see it when you grep for “include”

Secondly, the files “ValueTypes.td” and “MachineValueType.h” are redundant, and in a more typical system one would be generated from the other and “make” would keep them in sync, since that isn’t currently the case here both source files need top level comments to explain the situation and the need to manually keep the files in sync.  Such a comment needs to be in extreme bold case at the top of both files, it has to be impossible to not notice.

Thanks,
--Peter Lawrence.

From: Craig Topper [mailto:craig.topper at gmail.com]
Sent: Wednesday, May 25, 2016 10:45 PM
To: Lawrence, Peter <c_plawre at qca.qualcomm.com>
Cc: Marcello Maggioni <mmaggioni at apple.com>; llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] dumb question about tblgen

There is a comment in MachineValueTypes.h in the enum.

      // If you change this numbering, you must change the values in
      // ValueTypes.td as well!
      Other          =   0,   // This is a non-standard value

I don't think the .td include can be fixed easily. Tablegen doesn't support include guards and can only include each file once. Looks like there is a build step that runs tablegen directly on Intrinsics.td so that file needs to include ValueTypes.td on its own.

On Wed, May 25, 2016 at 10:20 PM, Lawrence, Peter <c_plawre at qca.qualcomm.com<mailto:c_plawre at qca.qualcomm.com>> wrote:
Craig,
           Ahha, thanks.

Even with that info I had to resort to “find-grep” to figure out how it gets #included,
Being indirectly included from “include/llvm/IR/Intrinsics.td” isn’t exactly obvious :=((

Would it be possible move the #include into “Target.td” ?

Also, in “ValueTypes.td” there is a comment about needing to keep it coordinated
With “MahineValueType.h”,  but there is no such comment in “MachineValueType.h”,

Would it be possible for someone to add such a complementary comment ?

Thanks,
--Peter Lawrence.

From: Craig Topper [mailto:craig.topper at gmail.com<mailto:craig.topper at gmail.com>]
Sent: Wednesday, May 25, 2016 9:31 PM
To: Marcello Maggioni <mmaggioni at apple.com<mailto:mmaggioni at apple.com>>
Cc: Lawrence, Peter <c_plawre at qca.qualcomm.com<mailto:c_plawre at qca.qualcomm.com>>; llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>

Subject: Re: [llvm-dev] dumb question about tblgen

The i32 class is defined in include/llvm/CodeGen/ValueTypes.td along with a class for every type in MachineValueTypes.h

On Wed, May 25, 2016 at 8:12 PM, Marcello Maggioni via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
I don’t quite follow why you are doing something like this.

What is the advantage of this instead of just attaching the AddrRegs regsister class as the register class for your instruction?
So that you would have an ADD instruction like
%AddrRegOut = ADD %AddrRegIn1, %AddrRegIn2

What kind of problematic regalloc are you trying to avoid with introducing a new backend data type?

Marcello
On 25 May 2016, at 19:07, Lawrence, Peter via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:

Quentin,
              My real problem is that my target has separate address and data registers.
The way I’d like to try getting better reg-alloc than I am now is to bring out the difference as
Early as possible, so I have added p16, p32, p64 to the enum in “MachineValueType.h”

And I have called  addRegisterClass(MVT::p32,  &XyzAddrRegsRegClass);

And I have an override for  virtual TargetLowering::getPointerTy()  that returns  MVT::p32,

And some other minor changes that altogether cause virt-regs that contain pointers
To get my  AddrRegs  reg-class rather than the “GPR” reg-class that i32 types get.

So far so good, except that llvm-tblgen barfs on “p32”,  so the question remains,
How does tblgen know the symbol names “i16”, “i32”, “i64”, etc...

They don’t seem to come from explicit “def” statements like the symbols “add”, “sub”, etc... do
Unless I’m missing something obvious (wouldn’t be the first time!)

And I’m mystified because my interpretation of reading “utils/TableGen/TableGen.cpp”
And “lib/TableGen/Main.cpp”,  Is that the input is fully read and parsed before the backend is invoked,
So the back-end can’t be providing symbol-table init for the front-end,
So the definitions have  to be in the input source, but I can’t find them…

Thanks,  Peter Lawrence.

From: Quentin Colombet [mailto:qcolombet at apple.com]
Sent: Wednesday, May 25, 2016 5:25 PM
To: Lawrence, Peter <c_plawre at qca.qualcomm.com<mailto:c_plawre at qca.qualcomm.com>>
Cc: llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>
Subject: Re: [llvm-dev] dumb question about tblgen

Hi Peter,

I would recommend looking into the implementation of the matcher if you want to add more builtin types:
utils/TableGen//DAGISelMatcherGen.cpp

That being said, you can define your own types without having to go through that hassle.
E.g., from AArch64
def simm9 : Operand<i64>, ImmLeaf<i64, [{ return Imm >= -256 && Imm < 256; }]> {
  let ParserMatchClass = SImm9Operand;
}

Wouldn’t that work for you?

Cheers,
-Quentin

On May 25, 2016, at 5:06 PM, Lawrence, Peter via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:

Dumb question about llvm-tblgen for “XyzGenInstrInfo.inc”

If I have a pattern in my dot-td-file like this

                [(set i32:$dst   (add i32:$rs1,  i32:$rs2))]

The question is where does the token “i32” come from,
I don’t see any definitions for i1, i8, i16, i32, …  in
                include/llvm/Target/*.td

while I do see definitions for tokens like “set”, “add”, …
coming from
                include/llvm/Target/TargetSelectionDAG.td

presumably these tokens are related to the enum in
                include/llvm/CodeGen/MachineValueType.h
but how does  tblgen know about them,

To put the question into context, if I add an item to the enum in “MachineValueType.h”
What do I do about
                “error: Variable not defined:”
Coming from tblgen when I try to use it in my dot-td-file,
I’ve already tried re-building tblgen, but that didn’t help.

thanks,
--Peter Lawrence.
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--
~Craig

--
~Craig
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