[llvm-dev] What pattern string corresponds to CopyToReg?

[Robert Baruch via llvm-dev]

Well, that's the thing: I thought that was CopyToReg. I don't know what the
name of the node is to load one value into a register, so I don't know how
to construct such a pattern.

On Sat, Nov 4, 2017 at 9:23 PM Craig Topper <craig.topper at gmail.com> wrote:

> Do you have a pattern for loading an i16 immediate into a 16-bit register?
>
> ~Craig
>
> On Sat, Nov 4, 2017 at 8:00 PM, Robert Baruch <robert.c.baruch at gmail.com>
> wrote:
>
>> Hmm, okay. Then what's the problem being reported here? I'm not sure what
>> I'm supposed to do with "LLVM ERROR: Cannot select: t1: i16 =
>> Constant<127>".BTW, the function is:
>>
>> ; ModuleID = 'return.c'
>> source_filename = "return.c"
>> target datalayout =
>> "E-m:e-p:16:16:16-i1:16:16-i8:16:16-i16:16:16-i32:16:16-i64:16:16-S16-n16"
>> target triple = "tms9900"
>>
>> ; Function Attrs: noinline nounwind optnone
>> define signext i16 @my_func() #0 {
>> entry:
>>   ret i16 127
>> }
>>
>> ------- debug output --------
>>
>> Optimized legalized selection DAG: BB#0 'my_func:entry'
>> SelectionDAG has 5 nodes:
>>     t0: ch = EntryToken
>>   t3: ch,glue = CopyToReg t0, Register:i16 %R5, Constant:i16<127>
>>   t4: ch = TMS9900ISD::Ret t3, Register:i16 %R5, t3:1
>>
>> ===== Instruction selection begins: BB#0 'entry'
>> Selecting: t4: ch = TMS9900ISD::Ret t3, Register:i16 %R5, t3:1
>>
>> ISEL: Starting pattern match on root node: t4: ch = TMS9900ISD::Ret t3,
>> Register:i16 %R5, t3:1
>>
>>   Morphed node: t4: ch,glue = Retr Register:i16 %R5, t3
>>
>> ISEL: Match complete!
>> Selecting: t3: ch,glue = CopyToReg t0, Register:i16 %R5, Constant:i16<127>
>>
>> Selecting: t2: i16 = Register %R5
>>
>> Selecting: t1: i16 = Constant<127>
>>
>> ISEL: Starting pattern match on root node: t1: i16 = Constant<127>
>>
>>   Initial Opcode index to 0
>>   Match failed at index 0
>> LLVM ERROR: Cannot select: t1: i16 = Constant<127>
>> In function: my_func
>>
>>
>> On Sat, Nov 4, 2017 at 7:22 PM Craig Topper <craig.topper at gmail.com>
>> wrote:
>>
>>> CopyToReg is not handle by patterns. It should be passed through isel
>>> unchanged. It’s part of a special list of ISD opcodes that don’t change in
>>> SelectioDAGISel::SelectCodeCommon
>>>
>>> It will then be turned into a TargetOpcode::COPY in
>>> InstrEmitter::EmitSpecialNode when the DAG is turned into MachineInstrs.
>>>
>>> On Sat, Nov 4, 2017 at 7:02 PM Robert Baruch via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>>> So there's a DAG that looks like this in the debug output:
>>>>
>>>>   Selecting: t3: ch,glue = CopyToReg t0, Register:i16 %R5,
>>>> Constant:i16<127>
>>>>
>>>> In the instruction selection phase, what pattern would that match? I've
>>>> constructed this so far:
>>>>
>>>>   (??? REG16:$dst, i16imm:$src)
>>>>
>>>> but the problem is, I can't determine what to use as ???. There is an
>>>> ISD::CopyToReg enum value, but I don't know how that translates to the
>>>> string to use in the pattern.
>>>>
>>>> And more generally, how do I find out from a DAG diagram like the ones
>>>> output by -view-isel-dags which node type corresponds to which pattern
>>>> string?
>>>>
>>>> Thanks,
>>>>
>>>> --Rob
>>>>
>>>> _______________________________________________
>>>> LLVM Developers mailing list
>>>> llvm-dev at lists.llvm.org
>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>
>>> --
>>> ~Craig
>>>
>>
>
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