[Mesa-dev] [PATCH] nir: allow stitching of non-empty block

[Caio Marcelo de Oliveira Filho]

This patch is

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira at intel.com>


On Fri, Jan 25, 2019 at 06:37:33PM +0100, Juan A. Suarez Romero wrote:
> When stitching two blocks A and B, where A's last instruction is a jump,
> it is not required that B is empty; it can be plainly removed.
> 
> This can happen in a situation like this:
> 
> vec1 1 ssa_1 = load_const (true)
> vec1 1 ssa_2 = load_const (false)
> block block_1:
> [...]
> loop {
>   vec1 ssa_3 = phi block_1: ssa_2, block_4: ssa_1
>   if ssa_3 {
>     block block_2:
>     [...]
>     break
>   } else {
>     block block_3:
>   }
>   vec1 ssa_4 = <alu operation>
>   if ssa_4 {
>     block block_4:
>     continue
>   } else {
>     block block_5:
>   }
>   block block_6:
>   [...]
> }
> 
> And opt_peel_loop_initial_if is applied. In this case, we would be
> ending up stitching block_2 (which finalizes with a jump) with
> block_4, which is not empty.
> 
> CC: Jason Ekstrand <jason at jlekstrand.net>
> ---
>  src/compiler/nir/nir_control_flow.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/src/compiler/nir/nir_control_flow.c b/src/compiler/nir/nir_control_flow.c
> index ddba2e55b45..27508f230d6 100644
> --- a/src/compiler/nir/nir_control_flow.c
> +++ b/src/compiler/nir/nir_control_flow.c
> @@ -550,7 +550,6 @@ stitch_blocks(nir_block *before, nir_block *after)
>      */
>  
>     if (nir_block_ends_in_jump(before)) {
> -      assert(exec_list_is_empty(&after->instr_list));
>        if (after->successors[0])
>           remove_phi_src(after->successors[0], after);
>        if (after->successors[1])
> -- 
> 2.20.1
> 
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	Caio