RE: [PATCH] Add support for a helper with 7 arguments

[Taylor Simpson]

Some of the more complex instructions need a lot of operands.  Here's an example
    if (Pv4) memb(Rs32 + Ru32 << #u2) = Rt32
This is a predicated store with 5 operands:
    Pv4predicate
    Rs32, Ru32, u2used to compute the effective address
    Rt32value to store
In addition, every helper gets an env argument, and predicated instructions get 
a "slot" argument.  The slot argument refers to the VLIW slot where the 
instruction is located within the packet.  It is used for predicated 
instructions to communicate to the end-of-packet handling to determine whether 
the instruction should commit.

So, the signature for the helper for this instruction is
    void HELPER(S4_pstorerbt_rr)(CPUHexagonState *env, int32_t PvV, int32_t 
RsV, int32_t RuV, int32_t RtV, int32_t uiV, uint32_t slot)

HTH,
Taylor

> -----Original Message-----
> From: Richard Henderson <address@hidden> On Behalf Of Richard
> Henderson
> Sent: Thursday, February 6, 2020 4:29 AM
> To: Taylor Simpson <address@hidden>; address@hidden
> Cc: Paolo Bonzini <address@hidden>
> Subject: Re: [PATCH] Add support for a helper with 7 arguments
>
> -------------------------------------------------------------------------
> CAUTION: This email originated from outside of the organization.
> -------------------------------------------------------------------------
>
> On 2/6/20 6:02 AM, Richard Henderson wrote:
> > On 2/5/20 10:41 PM, Taylor Simpson wrote:
> >> Currently, helpers can only take up to 6 arguments.  This patch adds the
> >> capability for up to 7 arguments.  I have tested it with the Hexagon port
> >> that I am preparing for submission.
> >
> > This is not safe, in general, without other changes.
> >
> >>From include/tcg/tcg.h:
> >
> >> /* While we limit helpers to 6 arguments, for 32-bit hosts, with padding,
> >>    this imples a max of 6*2 (64-bit in) + 2 (64-bit out) = 14 operands.
> >>    There are never more than 2 outputs, which means that we can store all
> >>    dead + sync data within 16 bits.  */
> >> #define DEAD_ARG  4
> >> #define SYNC_ARG  1
> >> typedef uint16_t TCGLifeData;
> >
> > Thus 7 uint64_t inputs, on a 32-bit host, will overflow TCGLifeData.
>
> My bad, no it won't.  For some reason I had two outputs in my head, but
> they'll
> both be uint32_t not two uint64_t.  7 uint64_t inputs with 1 uint64_t output
> will *just* fit.
>
>
> > What are you doing that requires so many arguments?
>
> But I'd still like to know why you need so many.
>
>
> r~