RFR(S): 8162384: Performance regression: bimorphic inlining may be bypassed by type speculation

[Vladimir Kozlov]

This looks good.

Thanks,
Vladimir

On 7/22/16 2:37 AM, Roland Westrelin wrote:
>
> http://cr.openjdk.java.net/~roland/8162384/webrev.00/
>
> Here is an example of that problem:
>
> private static int iterateIndirect(ByteBuffer buffer) {
>     int n = buffer.remaining();
>     while (n > 0 && buffer.get(n - 1) == 0) {
>         n--;
>     }
>     return n;
> }
>
> Profiling is:
>
> static ByteBufferTest::iterateIndirect(Ljava/nio/ByteBuffer;)I
>   interpreter_invocation_count: 2
>   invocation_counter: 2
>   backedge_counter: 156672
>   mdo size: 600 bytes
>
> 0 fast_aload_0
> 1 invokevirtual 49 <java/nio/ByteBuffer.remaining()I>
>   0 bci: 1 VirtualCallData count(0) nonprofiled_count(0) entries(1)
>                                     'java/nio/DirectByteBuffer'(1 1.00)
>                                     method_entries(0)
> 4 istore_1
> 5 iload_1
> 6 ifle 25
>   56 bci: 6 BranchData taken(0) displacement(144)
>                                     not taken(96249)
> 9 fast_aload_0
> 10 iload_1
> 11 iconst_1
> 12 isub
> 13 invokevirtual 50 <java/nio/ByteBuffer.get(I)B>
>   88 bci: 13 VirtualCallData trap/ ByteBufferTest::iterateIndirect(class_check recompiled) count(0) nonprofiled_count(0) entries(2)
>                                     'java/nio/HeapByteBuffer'(47103 0.49)
>                                     'java/nio/DirectByteBuffer'(49151 0.51)
>                                     method_entries(0)
> 16 ifne 25
>   144 bci: 16 BranchData trap(intrinsic_or_type_checked_inlining recompiled) flags(224) taken(1) displacement(56)
>                                     not taken(96254)
> 19 iinc #1 -1
> 22 goto 5
>   176 bci: 22 JumpData taken(96254) displacement(-120)
> 25 iload_1
> 26 ireturn
>
> The method is called with either a HeapByteBuffer or a DirectByteBuffer
> but profiling didn't run long enough to collect both at bci 1. The
> profiling at bci 1 (DirectByteBuffer) is fed to type speculation. Call
> at bci 13 uses the speculation, inlines DirectByteBuffer::get(). When a
> HeapByteBuffer is passed to the compiled method, an uncommon trap
> occurs, the method is recompiled eventually, speculation is used again
> to inline DirectByteBuffer::get() but because of the trap a virtual call
> is compiled to cover cases where the speculation fails. Given the
> profile data at the call, it would be much better to use bimorphic
> inlining and ignore speculation.
>
> Roland.
>