Re: [PATCH for-6.1] tcg/i386: Split P_VEXW from P_REXW

[Richard Henderson]

On 8/13/21 12:37 AM, Peter Maydell wrote:
> These changes look OK as far as they go, but it's not clear to
> me why the other places that set P_REXW are all OK to use P_REXW
> and not P_VEXW. For instance tcg_out_mov() sets rexw = P_REXW
> and some of the codepaths there will then pass that into
> tcg_out_vex_modrm() which ends up in tcg_out_vex_opc().

This distinguishes between 32-bit and 64-bit transfer between vector and general register. 
 Which of course doesn't make sense for i386.

> More generally, is there somewhere we can assert that we
> didn't try to use a REXW prefix for i386 codegen rather
> than just silently ignoring it ?

I guess tcg_out_opc might be a place.  But mostly we try to avoid generating those places 
in the first place.  E.g.

#if TCG_TARGET_REG_BITS == 64
# define OP_32_64(x) \
        case glue(glue(INDEX_op_, x), _i64): \
            rexw = P_REXW; /* FALLTHRU */    \
        case glue(glue(INDEX_op_, x), _i32)
#else
# define OP_32_64(x) \
        case glue(glue(INDEX_op_, x), _i32)
#endif


r~