RFR: 8256061: RegisterSaver::save_live_registers() omits upper halves of ZMM0-15 registers

[Sandhya Viswanathan]

On Mon, 9 Nov 2020 16:44:23 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

> `YMM0-15` registers are handled specially when CPU registers are saved. They are split in 2 parts (128-bit each) and put in different parts of the frame (see `RegisterSaver::layout` for details). AVX512 adds 16 more vector registers (ZMM16-31) and those are saved full-sized in a separate region. But `RegisterSaver::save_live_registers()` doesn't do anything special for `ZMM0-15` and their upper halves are lost (though there's space reserved for them in the frame).
> 
> The fix adds missing logic which saves upper halves (256-bit in size) of ZMM0-15 registers. Thus every ZMM0-15 register ends up split into 3 parts which are stored independently in the frame.
> 
> Testing (with some other relevant patches):
> - [x] jdk/incubator/vector w/ -XX:+DeoptimizeALot and -XX:UseAVX=3 on AVX512-capable hardware
> - [x] hs-precheckin-comp, hs-tier1, hs-tier2

It looks like the upper 256 bits of ZMM0-15 are already being saved as part of the following statements in sharedRuntime_x86_64.cpp:
 191   if (save_vectors) {
 192     // Save upper half of YMM registers(0..15)
 193     int base_addr = XSAVE_AREA_YMM_BEGIN;
 194     for (int n = 0; n < 16; n++) {
 195       __ vextractf128_high(Address(rsp, base_addr+n*16), as_XMMRegister(n));
 196     }
 197     if (VM_Version::supports_evex()) {
 198       // Save upper half of ZMM registers(0..15)
 199       base_addr = XSAVE_AREA_ZMM_BEGIN;
 200       for (int n = 0; n < 16; n++) {
 201         __ vextractf64x4_high(Address(rsp, base_addr+n*32), as_XMMRegister(n));
 202       }
 203       // Save full ZMM registers(16..num_xmm_regs)
 204       base_addr = XSAVE_AREA_UPPERBANK;
 205       off = 0;
 206       int vector_len = Assembler::AVX_512bit;
 207       for (int n = 16; n < num_xmm_regs; n++) {
 208         __ evmovdqul(Address(rsp, base_addr+(off++*64)), as_XMMRegister(n), vector_le
     n);
 209       }
 210     }
 211   }

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PR: https://git.openjdk.java.net/jdk/pull/1131