MVT-based vectors: first stab

Vladimir Ivanov vladimir.x.ivanov at oracle.com
Mon Jul 3 11:46:21 UTC 2017


> I was playing with some tests and your JDK patches seem to fix at least 
> 2 problems I've encountered when testing:

Glad to hear that. Thanks for testing!

I assume those are corresponding bugs I filed:

> * issues with double slots in lambda forms (wrong indices being 
> generated by LambaFormBuilder)

https://bugs.openjdk.java.net/browse/JDK-8183131
   core-libs/j.l.i [MVT] 2-slot type (long & double) support is broken 
in LambdaFormBuilder

> * issues with (un)boxing of method handles leading to bogus method call 
> results
https://bugs.openjdk.java.net/browse/JDK-8183132
   core-libs/j.l.i [MVT] MHI.unboxResultHandle misses unboxing step for 
Q-types

> Overall, I think your patches makes the situation a lot better - what's 
> the plan to check this code in? Do you want to make other iterations at 
> it? Or can we start the process?

On the JDK side, the changes are pretty sound in the current shape. I 
planned to shepherd the fixes into the repo, but neither did extensive 
testing nor finalized the actual fixes. Feel free to take care of them.

My near-term plans are: (1) implement missing LF intrinsics and (2) look 
into box elimination issues on JIT-compiler side.

Best regards,
Vladimir Ivanov

> On 28/06/17 14:17, Vladimir Ivanov wrote:
>> Hi,
>>
>> I started playing with MVT-based vectors recently and want to share my 
>> experience so far.
>>
>> For the first step, I decided to avoid specific treatment of 
>> super-longs (Long2/4/8) in the JVM we have in Panama and just mark 
>> them as VCCs for now:
>>   @DeriveValueType
>>   final class Long2 { public final long lo, hi; }
>>
>> As a test case I chose sum of array elements:
>>
>>   long sum(QLong2[] va) {
>>     QLong2 v = QLong2.default; // (0,0)
>>     for (int i = 0; i < va.length; i++) {
>>       QLong2 vi = va[i];
>>       v = QLong2(v.lo + vi.lo, v.hi + vi.hi);
>>     }
>>     return v.lo + v.hi;
>>   }
>>
>> Here are the changes:
>>  http://cr.openjdk.java.net/~vlivanov/valhalla/vectors.mvt/webrev.00/
>>
>> SUMMARY & RESULTS
>>
>> I hit some bugs along the way and had to extend the code for Q-types 
>> in some places to get decent code shape generated. (I'll shepherd the 
>> fixes in the repo separately.) I ended up with the following generated 
>> code:
>>
>> http://cr.openjdk.java.net/~vlivanov/valhalla/vectors.mvt/sumArrayL2.log
>>
>> Unfortunately, there are still 2 allocations left in the generated 
>> code (out of 5 initially). C2 can't scalarize the accumulator (v) 
>> inside the loop and has to put updated components (lo & hi) in 
>> allocated heap buffer on every iteration over the array (generated 
>> code [1], C2 EA output [2]).
>>
>>
>> GORY DETAILS
>>
>>   hotspot/src/share/vm/opto/type.cpp
>>
>>     * Type::get_typeflow_type() doesn't distinguish between 
>> TypeValueTypePtr & TypeValueType
>>
>>
>> jdk/src/java.base/share/classes/java/lang/invoke/LambdaFormBuilder.java
>>
>>     * introduced some LF intrinsics, e.g. LOOP and SELECT_ALTERNATIVE;
>>
>>     * had to workaround control flow-related bugs in the bytecode 
>> library (jdk.experimental.bytecode): broken JVM state after goto_() 
>> (see FIXME marks in the code);
>>
>>     * fixed 2-slot types support: wrong local indexes were used
>>
>>
>>
>> jdk/src/java.base/share/classes/java/lang/invoke/MethodHandleImpl.java
>>
>>     * MHI.unboxResultHandle misses unboxing step for Q-types
>>
>>
>> jdk/src/java.base/share/classes/java/lang/invoke/MethodHandles.java
>> jdk/src/java.base/share/classes/jdk/experimental/value/ValueType.java
>>
>>     * had to add a specialization for arraylength on Q-typed array, 
>> because C2 can't handle arraylength Object[] when Q[] instance is on 
>> stack;
>>
>>
>> jdk/src/java.base/share/classes/jdk/experimental/bytecode/TypedCodeBuilder.java: 
>>
>>
>>     * changes required to workaround goto_() bug
>>
>>     * fixed CP patching support
>>
>>
>> jdk/src/java.base/share/classes/jdk/experimental/value/MethodHandleBuilder.java 
>>
>>
>>     * fixed CP patching support
>>
>>
>>   hotspot/src/share/vm/memory/metachunk.hpp
>>   hotspot/src/share/vm/oops/method.hpp
>>     Fix optimized JVM build.
>>
>> Best regards,
>> Vladimir Ivanov
>>
>> [1] 
>> http://cr.openjdk.java.net/~vlivanov/valhalla/vectors.mvt/sumArrayL2.log
>>
>> ;; B7: # B8 <- B9  top-of-loop
>>
>> mov    %r9,0x10(%rsp)
>> mov    0x8(%rsp),%r11d
>>
>> ;; B8: # B16 B9 <- B6 B7   Loop: B8-B7 inner
>>
>> mov    %r11d,0x8(%rsp)
>> movabs $0x7c0060420,%rsi  ; {metadata('valhalla/vector/Long2$Value')}
>> ...
>> callq  0x0000000117579820 ;   {runtime_call _new_instance_Java}
>>
>> ;; B9: # B7 B10 <- B8
>>
>> mov    %rax,%r9
>> mov    0x10(%rsp),%r11
>> mov    0x10(%r11),%r10
>> mov    0x18(%r11),%r11
>> movslq %ebp,%r8
>> shl    $0x4,%r8
>> mov    (%rsp),%rcx
>> mov    0x18(%rcx,%r8,1),%rax
>> mov    0x10(%rcx,%r8,1),%r8  ;*vaload
>> add    %r11,%rax          ;*ladd
>> mov    %rax,0x18(%r9)
>> add    %r10,%r8           ;*ladd
>> mov    %r8,0x10(%r9)
>> inc    %ebp               ;*iadd
>> cmp    0x8(%rsp),%ebp
>> jl     <B7>               ;*if_icmpge
>>
>> [2] Pruned EA output (full output in the log)
>> ======== Connection graph for valhalla.vector.VectorTest::sumArrayL2
>> JavaObject NoEscape(NoEscape) NSR [ 1267F 1265F 756F 754F 1581F 1579F 
>> [ 1259 1264 532 1525 ]]   1247    Allocate
>> LocalVar [ 1247P [ 1264 ]]   1259    Proj ... #5
>> LocalVar [ 1259 1247P [ 1267b 1265b 532 1525 ]]   1264 CheckCastPP ... 
>> #valuetype* valhalla/vector/Long2$Value:NotNull
>> LocalVar [ 324 1264 1247P 307P [ 756b 754b ]]   532    Phi ... 
>> #valuetype* valhalla/vector/Long2$Value:NotNull
>> LocalVar [ 1264 324 1247P 307P [ 1581b 1579b ]]   1525    Phi ... 
>> #valuetype* valhalla/vector/Long2$Value:NotNull
>>
>> JavaObject NoEscape(NoEscape) [ 1154F [ 1148 1153 ]]   1136 Allocate
>> LocalVar [ 1136P [ 1153 ]]   1148    Proj ... #5
>> LocalVar [ 1148 1136P [ 1154b ]]   1153    CheckCastPP ... #valuetype* 
>> valhalla/vector/Long2$Value:NotNull
>>
>> JavaObject NoEscape(NoEscape) [ [ 1053 ]]   1041    Allocate
>> LocalVar [ 1041P [ ]]   1053    Proj ... #5
>>
>> JavaObject NoEscape(NoEscape) [ 653F 651F [ 645 650 ]]   633 Allocate
>> LocalVar [ 633P [ 650 ]]   645    Proj ... #5
>> LocalVar [ 645 633P [ 653b 651b ]]   650    CheckCastPP ... 
>> #valuetype* valhalla/vector/Long2$Value:NotNull
>>
>> JavaObject NoEscape(NoEscape) NSR [ 756F 754F 1581F 1579F [ 319 324 
>> 532 1525 ]]   307    Allocate
>> LocalVar [ 307P [ 324 ]]   319    Proj ... #5
>> LocalVar [ 319 307P [ 532 1525 ]]   324    CheckCastPP  ... 
>> #valuetype* valhalla/vector/Long2$Value:NotNull
>> LocalVar [ 324 1264 1247P 307P [ 756b 754b ]]   532    Phi ... 
>> #valuetype* valhalla/vector/Long2$Value:NotNull
>> LocalVar [ 1264 324 1247P 307P [ 1581b 1579b ]]   1525    Phi ... 
>> #valuetype* valhalla/vector/Long2$Value:NotNull
>>
>> Scalar  1153    CheckCastPP ... #valuetype* 
>> valhalla/vector/Long2$Value:NotNull
>> ++++ Eliminated: 1136 Allocate
>> Scalar  1041    Allocate ...
>> ++++ Eliminated: 1041 Allocate
>> Scalar  650    CheckCastPP ... #valuetype* 
>> valhalla/vector/Long2$Value:NotNull
>> ++++ Eliminated: 633 Allocate
> 


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