On Wed, 2016-08-17 at 11:54 -0700, Matt Turner wrote:
> The basic block following a control flow structure like an infinite
> loop
> will be unreachable. Ignore any non-control-flow instructions in it
> since they can have no effect on the program.
If the block is unreachable control-flow instructions inside the block
are also irrelevant, is there any reason why you don't skip CF
instructions too?
> Avoids a segmentation fault in cfg_t::intersect(a, b) when called on
> an
> unreachable block. By avoiding ever putting code in an unreachable
> block, we never attempt to optimize code in an unreachable block.
Can't the problem persist if the unreachable block has any control-flow
instructions?
> ---
> src/mesa/drivers/dri/i965/brw_cfg.cpp | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_cfg.cpp
> b/src/mesa/drivers/dri/i965/brw_cfg.cpp
> index 53b32be..2fa4e3d 100644
> --- a/src/mesa/drivers/dri/i965/brw_cfg.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_cfg.cpp
> @@ -312,6 +312,11 @@ cfg_t::cfg_t(exec_list *instructions)
> break;
>
> default:
> + if (cur->num != 0 && cur->parents.is_empty()) {
> + ip--;
> + continue;
> + }
> +
> cur->instructions.push_tail(inst);
> break;
> }
> @@ -319,6 +324,12 @@ cfg_t::cfg_t(exec_list *instructions)
>
> cur->end_ip = ip - 1;
>
> + /* If the last block was empty (because it was unreachable) drop
> it. */
> + if (cur->instructions.is_empty()) {
> + cur->link.remove();
> + num_blocks--;
> + }
> +
> make_block_array();
> }
>
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