Re: [Qemu-devel] [PATCH] tcg/i386: Fix dup_vec in non-AVX2 codepath

[Richard Henderson <rth@twiddle.net>]

On 05/04/2018 08:34 AM, Peter Maydell wrote:
> The VPUNPCKLD* instructions are all "non-destructive source",
> indicated by "NDS" in the encoding string in the x86 ISA manual.
> This means that they take two source operands, one of which is
> encoded in the VEX.vvvv field. We were incorrectly treating them
> as if they were destructive-source and passing 0 as the 'v'
> argument of tcg_out_vex_modrm(). This meant we were always
> using %xmm0 as one of the source operands, causing incorrect
> results if the register allocator happened to want to use
> something else. For instance the input AArch64 insn:
>  DUP v26.16b, w21
> which becomes TCG IR ops:
>  dup_vec v128,e8,tmp2,x21
>  st_vec v128,e8,tmp2,env,$0xa40
> was assembled to:
> 0x607c568c:  c4 c1 7a 7e 86 e8 00 00  vmovq    0xe8(%r14), %xmm0
> 0x607c5694:  00
> 0x607c5695:  c5 f9 60 c8              vpunpcklbw %xmm0, %xmm0, %xmm1
> 0x607c5699:  c5 f9 61 c9              vpunpcklwd %xmm1, %xmm0, %xmm1
> 0x607c569d:  c5 f9 70 c9 00           vpshufd  $0, %xmm1, %xmm1
> 0x607c56a2:  c4 c1 7a 7f 8e 40 0a 00  vmovdqu  %xmm1, 0xa40(%r14)
> 0x607c56aa:  00
> 
> when the vpunpcklwd insn should be "%xmm1, %xmm1, %xmm1".
> This resulted in our incorrectly setting the output vector to
> q26=0000320000003200:0000320000003200
> when given an input of x21 == 0000000002803200
> rather than the expected all-zeroes.

Oops.  Apparently I don't do enough testing on older machines.

> Pass the correct source register number to tcg_out_vex_modrm()
> for these insns.
> 
> Fixes: 770c2fc7bb70804a
> Cc: qemu-stable@nongnu.org
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  tcg/i386/tcg-target.inc.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)

Applied to tcg-next, thanks.


r~