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Re: [Qemu-devel] [PATCH v3 6/6] tcg/mips: Support r6 SEL{NE, EQ}Z instea
From: |
James Hogan |
Subject: |
Re: [Qemu-devel] [PATCH v3 6/6] tcg/mips: Support r6 SEL{NE, EQ}Z instead of MOVN/MOVZ |
Date: |
Fri, 9 Oct 2015 22:26:22 +0100 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Thu, Oct 08, 2015 at 06:31:32PM +0200, Aurelien Jarno wrote:
> On 2015-10-02 13:24, James Hogan wrote:
> > Extend MIPS movcond implementation to support the SELNEZ/SELEQZ
> > instructions introduced in MIPS r6 (where MOVN/MOVZ have been removed).
> >
> > Whereas the "MOVN/MOVZ rd, rs, rt" instructions have the following
> > semantics:
> > rd = [!]rt ? rs : rd
> >
> > The "SELNEZ/SELEQZ rd, rs, rt" instructions are slightly different:
> > rd = [!]rt ? rs : 0
> >
> > First we ensure that if one of the movcond input values is zero that it
> > comes last (we can swap the input arguments if we invert the condition).
> > This is so that it can exactly match one of the SELNEZ/SELEQZ
> > instructions and avoid the need to emit the other one.
> >
> > Otherwise we emit the opposite instruction first into a temporary
> > register, and OR that into the result:
> > SELNEZ/SELEQZ TMP1, v2, c1
> > SELEQZ/SELNEZ ret, v1, c1
> > OR ret, ret, TMP1
> >
> > Which does the following:
> > ret = cond ? v1 : v2
> >
> > Signed-off-by: James Hogan <address@hidden>
> > Cc: Richard Henderson <address@hidden>
> > Cc: Aurelien Jarno <address@hidden>
> > ---
> > Changes in v3:
> > - Switch to using bool eqz to indicate whether to use SELEQZ / MOVZ
> > instead of SELNEZ / MOVN (Richard).
> > - Add tcg_debug_assert(v2 == ret) for pre-r6 case with comment to remind
> > reader that it should be guaranteed via constraints (Richard).
> >
> > Changes in v2:
> > - Combine with patch 6 from v1, and drop functional changes to movcond
> > implementation pre-r6. We now provide different constraints for
> > movcond depending on presence of r6. (thanks Richard for feedback).
> > ---
> > tcg/mips/tcg-target.c | 43 +++++++++++++++++++++++++++++++++++++------
> > 1 file changed, 37 insertions(+), 6 deletions(-)
>
> Reviewed-by: Aurelien Jarno <address@hidden>
Thanks for the reviews Aurelien!
Cheers
James
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[Qemu-devel] [PATCH v3 3/6] tcg/mips: Add use_mips32r6_instructions definition, James Hogan, 2015/10/08
[Qemu-devel] [PATCH v3 4/6] tcg/mips: Support r6 JR encoding, James Hogan, 2015/10/08
[Qemu-devel] [PATCH v3 2/6] disas/mips: Add R6 jr/jr.hb to disassembler, James Hogan, 2015/10/08
[Qemu-devel] [PATCH v3 5/6] tcg/mips: Support r6 multiply/divide encodings, James Hogan, 2015/10/08