Re: [PATCH 11/21] Hexagon (target/hexagon) Short-circuit packet register writes

[Richard Henderson <richard.henderson@linaro.org>]

On 4/26/23 01:42, Taylor Simpson wrote:
> In certain cases, we can avoid the overhead of writing to hex_new_value
> and write directly to hex_gpr.  We add need_commit field to DisasContext
> indicating if the end-of-packet commit is needed.  If it is not needed,
> get_result_gpr() and get_result_gpr_pair() can return hex_gpr.
> 
> We pass the ctx->need_commit to helpers when needed.
> 
> Finally, we can early-exit from gen_reg_writes during packet commit.
> 
> There are a few instructions whose semantics write to the result before
> reading all the inputs.  Therefore, the idef-parser generated code is
> incompatible with short-circuit.  We tell idef-parser to skip them.
> 
> For debugging purposes, we add a cpu property to turn off short-circuit.
> When the short-circuit property is false, we skip the analysis and force
> the end-of-packet commit.
> 
> Here's a simple example of the TCG generated for
> 0x004000b4:  0x7800c020 {       R0 = #0x1 }
> 
> BEFORE:
>   ---- 004000b4
>   movi_i32 new_r0,$0x1
>   mov_i32 r0,new_r0
> 
> AFTER:
>   ---- 004000b4
>   movi_i32 r0,$0x1
> 
> Signed-off-by: Taylor Simpson<tsimpson@quicinc.com>
> ---

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~