RFR: 8266950: Remove vestigial support for non-strict floating-point execution [v2]

[Vladimir Ivanov]

>> I think there's `result->is_double_fpu()` check missing in 
>> `FpuStackAllocator::handle_op2`:
>>
>>       case lir_mul:
>>       case lir_div: {
>>         assert(op2->tmp1_opr()->is_fpu_register(), "strict operations 
>> need temporary fpu stack slot");
>>         insert_free_if_dead(op2->tmp1_opr());
>>         assert(sim()->stack_size() <= 7, "at least one stack slot must 
>> be free");
>>         // fall-through: continue with the normal handling of lir_mul 
>> and lir_div
>>       }
>>
>> The code should be guarded by `result->is_double_fpu()` since special 
>> handling (additional temp operand) is needed only for `mul`/`div` on 
>> doubles.
> 
> Where was that guard on the existing strict version?
> 
> This failure is suggesting to me that there may be a pre-existing bug in 
> the strict/non-strict code on x86. I need to check exactly what cases 
> the failing test is failing on so that I can see which code change is in 
> play. I have a suspicion but can't check it yet.

The guard was implicit: `lir_mul_strict`/`lir_div_strict` operations 
were always instantiated with the temp FPU operand. Since they are 
removed now, there's aliasing occurring between `lir_mul`/`lir_div` on 
doubles (`lir_mul_strict`/`lir_div_strict` before) and original 
operations on ints/longs/floats.

So, the check has to be explicit now. Only ddiv/dmul implementations 
need a temp operand.

Best regards,
Vladimir Ivanov