MVT-based vectors: first stab

Maurizio Cimadamore maurizio.cimadamore at oracle.com
Mon Jul 3 10:07:28 UTC 2017


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

* issues with double slots in lambda forms (wrong indices being 
generated by LambaFormBuilder)
* issues with (un)boxing of method handles leading to bogus method call 
results

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?

Cheers
Maurizio



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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