llvm dev - Aug 2017 - Disassembler/InstPrinter problem with implict output register.

Hi,

I'm defining the instructions for a microcontroller.
Most of the instructions have two explicit input registers, but the output
register is implicit for a given instruction.
For example, the output register for FADD instruction is FA_ROUTADD  while the
output register for the FMUL instruction is FA_ROUTMUL.
But the FA_ROUTADD nor the FA_ROUTMUL appears in the assembler syntax for the
instruction.

def       FADD_A_rr       : CLPFPU_A_rr_Inst<0b0000000101,
                                                (ins
FPUaRegisterOperand:$RegA,FPUaRegisterOperand:$RegB),
                                                (outs
FPUaROUTRegisterClass:$FA_ROUTADD),
                                                [RFLAGA],
                                                "fadd_a $RegA,$RegB",
                                                [(set f32:$FA_ROUTADD, (fadd
f32:$RegA, f32:$RegB))] >;

def       FMUL_A_rr        : CLPFPU_A_rr_Inst<0b0000001101,
                                                (ins
FPUaRegisterOperand:$RegA,FPUaRegisterOperand:$RegB),
                                                (outs
FPUaROUTRegisterClass:$FA_ROUTMUL),
                                                [RFLAGA],
                                                "fmul_a $RegA,$RegB",
                                                [(set f32:$FA_ROUTMUL, (fmul
f32:$RegA, f32:$RegB))] >;

The TableGen generated code consider these two instructions as three operands
instructions.
In the MCInst data structure, RegA and RegB are respectively the second and
third operands.
The place for the first operand seems to be reserved for the implicit output
register.
If I understand the need for such implicit register information, it is not clear
for me, when and who will populate this first operand.

My problem is that the default generated disassembler for now populate the RegA
and RegB in the first and second operands.
While the InstPrinter try to print the second and the third operands.

What is the most elegant way to address this issue? Any suggestions are welcome.

Regards,           Dominique Torette.







[http://www.spacebel.be/wp-content/uploads/2011/06/image-sign-sbp.jpg]

Dominique Torette
System Architect
Rue des Chasseurs Ardennais - Liège Science Park - B-4031 Angleur
Tel: +32 (0) 4 361 81 11 - Fax: +32 (0) 4 361 81 20
www.spacebel.be<http://www.spacebel.be/>



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