[9] RFR(S): 8144212: JDK 9 b93 breaks Apache Lucene due to compact strings

Fri Jan 15 18:14:28 UTC 2016

Very good.

Thanks,
Vladimir

On 1/13/16 4:00 AM, Tobias Hartmann wrote:
> Thanks, Vladimir.
>
> On 12.01.2016 20:24, Vladimir Kozlov wrote:
>>> My solution is to capture both the byte[] and char[] memory by using a MergeMem node as input to inflate_string.
>>
>> Yes, that is right solution here.
>
> I changed the implementation to only capture the byte[] and char[] memory:
> http://cr.openjdk.java.net/~thartmann/8144212/webrev.03/
>
> The method GraphKit::capture_memory(src_type, dst_type) returns a new MergeMemNode if the src and dst types are different, merging the two.
>
> Best,
> Tobias
>
>> On 1/12/16 5:59 AM, Tobias Hartmann wrote:
>>> On 11.01.2016 21:00, Vladimir Kozlov wrote:
>>>> On 1/11/16 7:20 AM, Tobias Hartmann wrote:
>>>>> On 08.01.2016 20:41, Vladimir Kozlov wrote:
>>>>>> On 1/8/16 2:37 AM, Tobias Hartmann wrote:
>>>>>>> On 07.01.2016 21:49, Vladimir Kozlov wrote:
>>>>>>>> On 1/7/16 6:52 AM, Tobias Hartmann wrote:
>>>>>>>>> Hi Vladimir,
>>>>>>>>>
>>>>>>>>> On 07.01.2016 00:58, Vladimir Kozlov wrote:
>>>>>>>>>> Andrew is right.
>>>>>>>>>
>>>>>>>>> Yes, he's right that the membar is not needed in this case. I noticed that GraphKit::inflate_string() sets the output memory to TypeAryPtr::BYTES although inflate writes to a char[] array in this case. This caused the subsequent char load to be on a different slice allowing C2 to move the load to before the intrinsic.
>>>>>>>>
>>>>>>>> Right. It was the root of this bug, see below.
>>>>>>>>
>>>>>>>>>
>>>>>>>>> I fixed this for the inflate and compress intrinsics.
>>>>>>>>>
>>>>>>>>>> GraphKit::inflate_string() should have SCMemProjNode as compress_string() does to prevent loads move up.
>>>>>>>>>> StrInflatedCopyNode is not memory node.
>>>>>>>>>
>>>>>>>>> Okay, why are above changes not sufficient to prevent the load from moving up? Also, the comment for SCMemProjNode says:
>>>>>>>>
>>>>>>>> I did not get the question. Is it before your webrev.01 change? Or even with the change?
>>>>>>>
>>>>>>> I meant with webrev.01 but you answered my question below.
>>>>>>>
>>>>>>>>>       // This class defines a projection of the memory  state of a store conditional node.
>>>>>>>>>       // These nodes return a value, but also update memory.
>>>>>>>>>
>>>>>>>>> But inflate does not return any value.
>>>>>>>>
>>>>>>>> Hmm, according to bottom type inflate produce memory:
>>>>>>>>
>>>>>>>> StrInflatedCopyNode::bottom_type() const { return Type::MEMORY; }
>>>>>>>>
>>>>>>>> So it really does not need SCMemProjNode. Sorry about that.
>>>>>>>> So load was LoadUS which is char load and originally memory slice of inflate was incorrect BYTES.
>>>>>>>
>>>>>>> Exactly.
>>>>>>>
>>>>>>>> Instead of SCMemProjNode we should have to change the idx of your dst_type:
>>>>>>>>
>>>>>>>> set_memory(str, dst_type);
>>>>>>>
>>>>>>> Yes, that's what I do now in webrev.01 by passing the dst_type as an argument to inflate_string.
>>>>>>>
>>>>>>>> And you should rollback part of changes in escape.cpp and macro.cpp.
>>>>>>>
>>>>>>> Okay, I'll to that.
>>>>>>>
>>>>>>>>> Here is the new webrev, including the SCMemProjNode and adapting escape analysis and macro expansion accordingly:
>>>>>>>>> http://cr.openjdk.java.net/~thartmann/8144212/webrev.01/
>>>>>>>>
>>>>>>>> In general when src & dst arrays have different type we may need to use TypeOopPtr::BOTTOM to prevent related store & loads bypass these copy nodes.
>>>>>>>
>>>>>>> Okay, should we then use BOTTOM for both the input and output type?
>>>>>>
>>>>>> Only input. Output type corresponds to dst array type which you set correctly now.
>>>>>
>>>>> It seems like that this is not sufficient. As Roland pointed out (off-thread), there may still be a problem in the following case:
>>>>>     StoreC
>>>>>     inflate_string
>>>>>     LoadC
>>>>>
>>>>> The memory graph (def->use) now looks like this:
>>>>>     LoadC -> inflate_string -> ByteMem
>>>>>                   ... StoreC-> CharMem
>>>>
>>>> I did not get this. If StoreC node is created before inflate_string - inflate_string should point to it be barrier for LoadC.
>>>
>>> Note that the StoreC and inflate_string are *not* writing to the same char[] array. The test looks like this:
>>>
>>>    char c1[] = new char[1];
>>>    char c2[] = new char[1];
>>>
>>>    c2[0] = 42;
>>>    // Inflate String from byte[] to char[]
>>>    s.getChars(0, 1, c1, 0);
>>>    // Read char[] memory written before inflation
>>>    return c2[0];
>>>
>>> The result should be 42. The problem is that inflate_string does not point to StoreC because inflate_string uses a byte[] as input and in this case also writes to a different char[]. Even if we set the input to BOTTOM, inflate_string points to 7 Parm (BOTTOM) but not to the char[] memory produced by 96 StoreC:
>>> http://cr.openjdk.java.net/~thartmann/8144212/inflate_bottom.png
>>>
>>> 349 LoadUS then reads from the output char[] memory of inflate_string which does not include the result of StoreC. The test fails because the return value is != 42.
>>>
>>> My solution is to capture both the byte[] and char[] memory by using a MergeMem node as input to inflate_string.
>>>
>>>>    If StoreC followed inflate_string and LoadC followed StoreC - LoadC should point to StoreC. If LoadC does not follow StoreC then result is relaxed.
>>>
>>> Yes, these cases work fine.
>>>
>>> Thanks,
>>> Tobias
>>>
>>>>> The intrinsic hides the dependency between LoadC and StoreC, causing the load to read from memory not containing the result of the StoreC. I was able to write a regression test for this (see 'TestStringIntrinsicMemoryFlow::testInflate2').
>>>>>
>>>>> Setting the input to BOTTOM, generates the following graph:
>>>>> http://cr.openjdk.java.net/~thartmann/8144212/inflate_bottom.png
>>>>> The 349 LoadUS does not read the result of the 96 StoreC because the StrInflateCopyNode does not capture it's memory. The test fails.
>>>>>
>>>>> I adapted the fix to emit a MergeMemoryNode to capture the entire memory state as input to the intrinsic. The graph then looks like this:
>>>>>     LoadC -> inflate_string -> MergeMem(ByteMem, StoreC(CharMem))
>>>>> http://cr.openjdk.java.net/~thartmann/8144212/inflate_merge.png
>>>>>
>>>>> Here is the new webrev:
>>>>> http://cr.openjdk.java.net/~thartmann/8144212/webrev.02/
>>>>> Probably, we could also only capture the byte and char slices instead of merging everything. What do you think?
>>>>>
>>>>> Best,
>>>>> Tobias
>>>>>
>>>>>>>>> Related question:
>>>>>>>>> In library_call.cpp, I now use TypeAryPtr::get_array_body_type(dst_elem) to get the correct TypeAryPtr for the destination (we support both BYTES and CHARS). For a char[] destination, it returns:
>>>>>>>>>       char[int:>=0]:exact+any *
>>>>>>>>>
>>>>>>>>> which is equal to the type of the char load.
>>>>>>>>
>>>>>>>> Please, explain this. I thought string's array will always be byte[] when compressed strings are enabled. Is it used for getChars() which returns char array?
>>>>>>>
>>>>>>> Yes, both the compress and inflate intrinsics are used for different types of src and dst arrays. See comment in library_call.cpp:
>>>>>>>
>>>>>>> // compressIt == true --> generate a compressed copy operation (compress char[]/byte[] to byte[])
>>>>>>> //   int StringUTF16.compress(char[] src, int srcOff, byte[] dst, int dstOff, int len)
>>>>>>> //   int StringUTF16.compress(byte[] src, int srcOff, byte[] dst, int dstOff, int len)
>>>>>>> // compressIt == false --> generate an inflated copy operation (inflate byte[] to char[]/byte[])
>>>>>>> //   void StringLatin1.inflate(byte[] src, int srcOff, char[] dst, int dstOff, int len)
>>>>>>> //   void StringLatin1.inflate(byte[] src, int srcOff, byte[] dst, int dstOff, int len)
>>>>>>>
>>>>>>> I.e., the inflate intrinsic is used for inflation from byte[] to byte[]/char[].
>>>>>>>
>>>>>>>> Should we also be more careful in inflate_string_slow()? Is it used?
>>>>>>>
>>>>>>> No, inflate_string_slow() is only called from PhaseStringOpts::copy_latin1_string() where it is used to inflate from byte[] to byte[].
>>>>>>>
>>>>>>>>> I also tried to derive the type from the array by using dst_type->isa_aryptr(). However, this returns a more specific type:
>>>>>>>>>       char[int:1]:NotNull:exact *
>>>>>>>>>
>>>>>>>>> Using this results in C2 assuming that the subsequent char load is independent and again moving it to before the intrinsic. I don't understand why that is. Shouldn't the second type be a "subtype" of the first type?
>>>>>>>>
>>>>>>>> It is indeed strange. What memory type of LoadUS? It could be bug.
>>>>>>>
>>>>>>> LoadUS has memory type "char[int:>=0]:exact+any *" which has alias index 4. dst_type->isa_aryptr() returns memory type "char[int:1]:NotNull:exact *" which has alias index 8.
>>>>>>>
>>>>>>> I will look into this again and try to understand what happens.
>>>>>>
>>>>>> It could that aryptr is pointer to array and load type is pointer to array's element.
>>>>>>
>>>>>> Thanks,
>>>>>> Vladimir
>>>>>>
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Tobias
>>>>>>>
>>>>>>>>>> On 1/6/16 5:34 AM, Andrew Haley wrote:
>>>>>>>>>>> On 01/06/2016 01:06 PM, Tobias Hartmann wrote:
>>>>>>>>>>>
>>>>>>>>>>>> The problem here is that C2 reorders memory instructions and moves
>>>>>>>>>>>> an array load before an array store. The MemBarCPUOrder is now used
>>>>>>>>>>>> (compiler internally) to prevent this. We do the same for normal
>>>>>>>>>>>> array copys in PhaseMacroExpand::expand_arraycopy_node(). No actual
>>>>>>>>>>>> code is emitted. See also the comment in memnode.hpp:
>>>>>>>>>>>>
>>>>>>>>>>>>        // Ordering within the same CPU.  Used to order unsafe memory references
>>>>>>>>>>>>        // inside the compiler when we lack alias info.  Not needed "outside" the
>>>>>>>>>>>>        // compiler because the CPU does all the ordering for us.
>>>>>>>>>>>>
>>>>>>>>>>>> "CPU does all the ordering for us" means that even with a relaxed
>>>>>>>>>>>> memory ordering, loads are never moved before dependent stores.
>>>>>>>>>>>>
>>>>>>>>>>>> Or did I misunderstand your question?
>>>>>>>>>>>
>>>>>>>>>>> No, I don't think so.  I was just checking: I am very aware that
>>>>>>>>>>> HotSpot has presented those of use with relaxed memory order machines
>>>>>>>>>>> with some interesting gotchas over the years, that's all.  I'm a bit
>>>>>>>>>>> surprised that C2 needs this barrier, given that there is a
>>>>>>>>>>> read-after-write dependency, but never mind.
>>>>>>>>>>>
>>>>>>>>>>> Thanks,
>>>>>>>>>>>
>>>>>>>>>>> Andrew.
>>>>>>>>>>>