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

[Vladimir Kozlov]

Assembler part review.

In stubGenerator_sparc.cpp

Move next lines above 64 bit value construction:

+     __ cmp(count, 2<<shift); // Short arrays (< 8 bytes) copy by element
+     __ brx(Assembler::lessUnsigned, false, Assembler::pn, L_copy_4_bytes); // use unsigned cmp
+     __ delayed()->nop();

In assembler_x86.cpp

You don't need next:
+     jmpb(L_copy_4_bytes); // all dwords were copied

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);

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