review (M) for 4809552: Optimize Arrays.fill(...)

[Vladimir Kozlov]

Tom Rodriguez wrote:
> 
>> Use next movdqa since you aligned address:
>> +         movdqa(Address(to, 0), xtmp);
>> +         movdqa(Address(to, 16), xtmp);
>>
>> instead of
>> +         movq(Address(to, 0), xtmp);
>> +         movq(Address(to, 8), xtmp);
>> +         movq(Address(to, 16), xtmp);
>> +         movq(Address(to, 24), xtmp);
> 
> But it's only aligned to 8 bytes, not 16.  maybe it would be worth it to align to 16?

Sorry, you are right, it requires 16 not 8 bytes. :(
I think it worth to align to 16 since it will benefit all x86.

       movdl(xtmp, value);
       pshufd(xtmp, xtmp, 0);

+     // align to 16 bytes, we know we are 8 byte aligned to start
+     Label L_skip_align16;
+     testptr(to, 8);
+     jccb(Assembler::zero, L_skip_align16);
+     subl(count, 2<<shift);
+     jcc(Assembler::below, L_copy_4_bytes); // Short arrays (< 8 bytes)
+     movq(Address(to, 0), xtmp);
+     addptr(to, 8);
+     BIND(L_skip_align16);

       subl(count, 8 << shift);
       jcc(Assembler::less, L_check_fill_8_bytes);
       align(16);

Vladimir

> 
> tom
> 
>> Vladimir
>>
>> Vladimir Kozlov wrote:
>>> Tom,
>>> First, I would not call these changes Medium. They are Large at least.
>>> Should we allow OptimizeFill only when UseLoopPredicate is true?
>>> loopTransform.cpp:
>>> In match_fill_loop() should we exclude StoreCMNode also?
>>> RAW store check is hidden in as_AddP()->unpack_offsets(). Should we do it explicitly?
>>> store and store_value is not set for "copy candidate":
>>> +         if (value->is_Load() && lpt->_body.contains(value)) {
>>> +           // tty->print_cr("possible copy candidate");
>>> +         } else {
>>> +           msg  = "variant store value";
>>> +         }
>>> Why you assume that on 'else' it is mem_phi?:
>>> +       if (n == head->phi()) {
>>> +         // ok
>>> +       } else {
>>> +         // mem_phi
>>> +       }
>>> Should we also skip proj node (ifFalse) or it is not part of loop body?
>>> +     } else if (n->is_CountedLoopEnd()) {
>>> +       // ok so skip it.
>>> +           msg = "node used outside loop";
>>>                       ^ is
>>> How you translate next assert message?:
>>> +     assert(store_value->is_Load(), "shouldn't only happen for this case");
>>> the next dump should be under flag and 'msg' should reflect "possible copy" or set msg_node:
>>> + #ifdef ASSERT
>>> +     tty->print_cr("possible copy");
>>> +     store_value->dump();
>>> +     store->dump();
>>> + #endif
>>> +     msg = "variant store in loop";
>>> For Op_LShiftX there is no check (n->in(1) == head->phi()):
>>> +       } else if (n->Opcode() == Op_LShiftX) {
>>> +         shift = n;
>>> +         assert(type2aelembytes(store->as_Mem()->memory_type(), true) == 1 << shift->in(2)->get_int(), "scale should match");
>>> s_offs already includes base_offset, see GraphKit::array_element_address():
>>> +     aligned = ((arrayOopDesc::base_offset_in_bytes(t) + s_offs * element_size) % HeapWordSize == 0);
>>> Also the above expression is wrong if initial index != 0.
>>> And actually you don't need to calculate it in match_fill_loop() since
>>> it is used only in call to StubRoutines::select_fill_function() to verify
>>> that element type is supported.
>>> In intrinsify_fill() initial index value is taking into account for aligned
>>> but base_offset_in_bytes could be already part of offset and you need
>>> to multiply by element_size only initial index:
>>> +   if (offset != NULL && head->init_trip()->is_Con()) {
>>> +     intptr_t offs = offset->find_intptr_t_type()->get_con() + head->init_trip()->get_int();
>>> +     int element_size = type2aelembytes(t);
>>> +     aligned = ((arrayOopDesc::base_offset_in_bytes(t) + offs * element_size) % HeapWordSize == 0);
>>> +   }
>>> stubRoutines.cpp:
>>> why you have specialized copies for testing _jint_fill and _jbyte_fill. Is not it covered by TEST_FILL already?
>>> stubGenerator_sparc.cpp:
>>> +   //  Generate stub for disjoint short fill.  If "aligned" is true, the
>>>      ^ Generate stub for array fill.
>>> +   //      from:  O0
>>>            ^ to
>>> +   //      to:    O1
>>>            ^ value
>>> O5 is not used and not input argument:
>>> +     const Register offset    = O5;   // offset from start of arrays
>>> stubs are generated only for byte,short and int, so allowing bollean, char and float is wrong:
>>> +     switch (t) {
>>> +       case T_BOOLEAN:
>>> +       case T_BYTE:
>>> +         shift = 2;
>>> +         break;
>>> +       case T_CHAR:
>>> +       case T_SHORT:
>>> +         shift = 1;
>>> +         break;
>>> +       case T_FLOAT:
>>> +       case T_INT:
>>> +         shift = 0;
>>> +         break;
>>> +       default: ShouldNotReachHere();
>>> +     }
>>> The same in assembler_x86.cpp
>>> In stubGenerator_x86_64.cpp
>>> new fill_32_bytes_forward() is not used.
>>> Remove commented code for T_LONG in both stubGenerator_x86_??.cpp
>>> I did not look on assembler. May be tomorrow.
>>> Thanks,
>>> Vladimir
>>> Tom Rodriguez wrote:
>>>> 4809552: Optimize Arrays.fill(...)
>>>> Reviewed-by:
>>>>
>>>> This adds new logic to recognize fill idioms and convert them into a
>>>> call to an optimized fill routine.  Loop predication creates easily
>>>> matched loops that are simply replaced with calls to the new assembly
>>>> stubs.  Currently only 1,2 and 4 byte primitive types are supported.
>>>> Objects and longs/double will be supported in a later putback.  Tested
>>>> with runthese, nsk and ctw plus jbb2005.
>>>>
>>>> http://cr.openjdk.java.net/~never/4809552
>