Re: [Qemu-devel] [PATCH 7/7] target/arm: Use tcg_gen_extrh_i64_i32 to extract the high word

[Peter Maydell]

On Thu, 15 Aug 2019 at 12:56, Richard Henderson
<address@hidden> wrote:
>
>
>
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> >
> >This patch is fine, but I noticed while reviewing it that tcg/README
> >labels both the extrl_i64_i32 and extrh_i64_i32 operations as
> >"for 64-bit hosts only". Presumably that's a documentation error,
> >since we're not guarding the existing uses of the extrl_i64_i32
> >here with any kind of ifdeffery to restrict them to 64-bit hosts ?
> >
>
>
> A documentation unclarity in that the opcodes are for 64-bit hosts. The 
> tcg_gen_* functions are always available, and expand to INDEX_op_mov_i32 on 
> 32-bit hosts.

Oh, I see. We should probably split that document out properly
into a primary "what you need to know to generate TCG code as
a target" (which is the main audience) and "what you need to
implement for a TCG backend (which I guess is relevant to fewer
people).

thanks
-- PMM