[9] RFR(S): 8148490: RegisterSaver::restore_live_registers() fails to restore xmm registers on 32 bit
Vladimir Kozlov
vladimir.kozlov at oracle.com
Fri Jan 29 19:39:45 UTC 2016
Tobias, please verify that 64-bit code works correctly.
About 32-bit code.
Please verify correctness of next asserts:
assert(UseAVX > 0, "512bit vectors are supported only with EVEX");
assert(MaxVectorSize == 64, "only 512bit vectors are supported now");
Originally we could have vectors even with only 64bit XMM registers. MaxVectorSize and UseAVX can be set on command line
- what happens in such case? No vectorization?
May be it is done because we save whole 128bit XMM always. Still MaxVectorSize == 64 condition is strange.
Thanks,
Vladimir
On 1/29/16 6:16 AM, Tobias Hartmann wrote:
> Hi,
>
> please review the following patch:
> https://bugs.openjdk.java.net/browse/JDK-8148490
> http://cr.openjdk.java.net/~thartmann/8148490/webrev.00/
>
> RegisterSaver::save_live_registers() and RegisterSaver::restore_live_registers() are used by the safepoint handling code to save and restore registers. The following code is emitted to save and restore XMM/YMM registers on 32 bit:
>
> Save:
> ...
> 0xf34ca12e: vmovdqu %xmm0,0xb0(%esp)
> 0xf34ca137: vmovdqu %xmm1,0xc0(%esp)
> ...
> 0xf34ca16d: vmovdqu %xmm7,0x120(%esp)
> 0xf34ca176: sub $0x80,%esp
> 0xf34ca17c: vextractf128 $0x1,%ymm0,(%esp)
> 0xf34ca183: vextractf128 $0x1,%ymm1,0x10(%esp)
> ...
> 0xf34ca1b3: vextractf128 $0x1,%ymm7,0x70(%esp)
> ...
>
> Restore:
> ...
> 0xf34ca202: vinsertf128 $0x1,(%esp),%ymm0,%ymm0
> 0xf34ca209: vinsertf128 $0x1,0x10(%esp),%ymm1,%ymm1
> ...
> 0xf34ca239: vinsertf128 $0x1,0x70(%esp),%ymm7,%ymm7
> 0xf34ca241: add $0x80,%esp
> 0xf34ca247: vmovdqu 0x130(%esp),%xmm0
> 0xf34ca250: vmovdqu 0x140(%esp),%xmm1
> ...
> 0xf34ca286: vmovdqu 0x1a0(%esp),%xmm7
> ...
>
> The stack offsets for the vmovdqu instructions are wrong, causing the XMM registers to contain random values after a safepoint. The problem is that "additional_frame_bytes" is added to the stack offset although the stack pointer is incremented just before:
>
> 283 __ addptr(rsp, additional_frame_bytes); // Save upper half of YMM registers
>
> The regression test fails with "Test failed: array[0] = 1973.0 but should be 10.000" because the vectorized loop returns a wrong result.
>
> I spotted and fixed the following other problems:
> - the vmovdqu instructions should be emitted before restoring YMM and ZMM because they zero the upper part of the XMM registers (i.e. YMM/ZMM)
> - if 'UseAVX > 2' is set/available, we save the ZMM registers as well but we do not increment 'additional_frame_words' accordingly (we need another 8*32 bytes of stack space)
>
> Unfortunately, I don't have access to a CPU with the AVX-512 instruction set to test the "UseAVX > 2" related changes. Michael, could you verify the changes?
>
> The problems were introduced by the fix for JDK-8142980.
>
> Thanks,
> Tobias
>
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