[llvm-dev] how to add a instruction

[Tianhao Shen via llvm-dev]

Thank you for answering my questions.
I don't understand how to disarm the constraints, because I want to my  instruction like  "c=max_qb(a,b)".
Thank you again.
Tianhao Shen.


On 11/8/2018 01:33，Craig Topper<craig.topper at gmail.com> wrote：
The "Unhandled immediate encoding GR32" is fixed by the "let Constraints = "$src1 = $dst". That tells the disassembler, encoder, and register allocator that $src1 and $dst must always be the same physical register. This is true of all the basic X86 arithmetic instructions where one of the inputs is always overwritten by the output.


~Craig




On Tue, Nov 6, 2018 at 11:26 PM Tianhao Shen via llvm-dev <llvm-dev at lists.llvm.org> wrote:

Hi,every one.
I' in trouble again.
I want add a new intrinsic mapping a new instruction.


I add the int_x86_max_qb as fllowing:
def int_x86_max_qb: GCCBuiltin<"__builtin_x86_max_qb">, Intrinsic<[llvm_i32_ty], [llvm_i32_ty, llvm_i32_ty], [Commutative]>;


BUILTIN(__builtin_x86_max_qb, "iii", "") 


I define the intrinsic as Pseudo instruction,it succeed.


But when mapping a new instruction.I don't know how to do.
In x86InstrArithmetic.td. I add ,(To make sure the Sched is right, I use the WriteIMul16Reg )
def max_qb : I<0xF0,MRMSrcReg, (outs  GR32:$dst), (ins GR32:$src1,GR32:$src2), "max_qb\t {$dst, $src1,$src2}", [(set GR32:$dst,(X86max_qb GR32:$src1, GR32:$src2))]>,Sched<[WriteIMul16Reg]>,OpSize32 ;
when compile LLVM , the error appears.
"[ 97%] Updating X86GenAsmWriter1.inc...   
Unhandled immediate encoding GR32
Unhandled immediate encoding
"


But when I write the same as the instruction IMUL32rr, there is no error in compiling.(I don't use the EFLAGS at all, so I think it's wrong. Indeed, it made a error when using it.)
let Defs = [EFLAGS] in {
let Constraints = "$src1 = $dst" in {
let isCommutable = 1 in {
def max_qb : I<0xF0,MRMSrcReg, (outs  GR32:$dst), (ins GR32:$src1,GR32:$src2), "max_qb\t {$dst, $src1,$src2}", [(set GR32:$dst,(X86max_qb GR32:$src1, GR32:$src2))]>,Sched<[WriteIMul16Reg]>,OpSize32 ;
}
}


What I don't understand is that how I define "let   in  ".
Thanks,
Tianhao Shen.




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