[llvm-dev] Unsigned int displaying as negative

[Ryan Taylor via llvm-dev]

I believe that the idea of simm16 and uimm16 was taken over from
MipsInstrInfo.td. It's entirely possible that the concepts were
misunderstood then.

So, a broader question, what is the best way to map down to an
unsigned/signed sub/add (is this even possible)? How to add signed/unsigned
immediates?

Thanks.

On Wed, Feb 15, 2017 at 3:14 PM, Friedman, Eli <efriedma at codeaurora.org>
wrote:

> On 2/15/2017 11:37 AM, Ryan Taylor via llvm-dev wrote:
>
>> I see. If I put simm16 and immSExt16x in place of uimm16 and immZExt16x
>> respectively, the imm matches but it prints out -32768 (which is invalid
>> for sub16u). We are using uimm16 not match unsigned but for PrintMethod,
>> effectively uimm16 and simm16 are both Operand<i16>. I'm still unclear why
>> simm16 matches and uimm16 does not. Here is the pattern if that helps at
>> all.
>>
>> So just as a reference:
>>
>> def simm16      : Operand<i16> {
>>   let DecoderMethod= "DecodeSimm16";
>>   let OperandType = "OPERAND_IMMEDIATE";
>> }
>>
>> def uimm16      : Operand<i16> {
>>   let PrintMethod = "printUnsignedImm";
>>   let OperandType = "OPERAND_IMMEDIATE";
>> }
>>
>> def immSExt16x : ImmLeaf<i16, [{ return isInt<16>(Imm); }]>;
>> def immZExt16x : ImmLeaf<i16, [{ return isUInt<16>(Imm); }]>;
>>
>
> "Imm" in ImmLeaf is an int64_t, sign-extended from your immediate type (in
> this case, int16_t).  You'd need to insert an explicit cast to uint16_t to
> get the behavior you want.
>
> I'm not sure why you're doing this, though; every 16-bit integer immediate
> fits into a 16-bit integer, so a correctly implemented "immZExt16x" is just
> equivalent to "imm".
>
>
> -Eli
>
> --
> Employee of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux
> Foundation Collaborative Project
>
>
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