It depends on whether the target machine has 16-bit register operands.
Strictly speaking, I2I2ILOAD means loading a 16-bit data to a 16-bit
register. I4I2ILOAD means loading from a 16-bit location and expanding
the result to make it occupy a 32-bit register, which can be translated
to one machine instruction for most architectures. If the target does
not have 16-bit register, then it is not clear what I2I2ILOAD will
translate to. (In x86, even though there are the legacy 16-bit
registers, like ax, bx, we never really use them in the compiler.)
Fred
On 01/12/2011 07:03 AM, Sun Chan wrote:
> unless you have 2byte size load instruction, the whirl will require
> multiple instructions which will affect final code quality, this is my
> understanding. Fred, is this your rationale?
>
> Sun
>
> On Wed, Jan 12, 2011 at 10:37 PM, Jian-Xin Lai<laij...@gmail.com> wrote:
>> Hi,
>>
>> I was trying to make an I2I2ILOAD but got an assertion about "bad opcode
>> ILOAD, MTYPE_I2, MTYPE_I2". I think I2I2ILOAD should be legal but it looks
>> I'm wrong.
>> In opt/opt_htable.cxx, I saw this kind of code:
>> 4126 #ifdef TARG_SL
>> 4127 if (dtyp == MTYPE_I2&& dsctyp == MTYPE_I2) {
>> 4128 dtyp = MTYPE_I4;
>> 4129 }
>> 4130 #endif
>> 4131 opc = OPCODE_make_op(opr == OPR_ISTORE ? OPR_ILOAD :
>> OPR_ILDBITS, dtyp, dsctyp);
>>
>> It looks in TARG_SL, they changes the rtype to I4 to avoid generating
>> I2I2ILOAD. Could someone explain why I2I2ILOAD is not allowed? Thank you
>> very much.
>>
>> --
>> Regards,
>> Lai Jian-Xin
>>
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