[Mesa-dev] [PATCH 1/5] i965: Keep pointers to IF/ELSE/ENDIF instructions in the cfg.

[Paul Berry]

On 31 October 2013 18:57, Matt Turner <mattst88 at gmail.com> wrote:

> Useful for finding the associated control flow instructions, given a
> block ending in one.
> ---
>  src/mesa/drivers/dri/i965/brw_cfg.cpp | 34
> ++++++++++++++++++++++++++++++----
>  src/mesa/drivers/dri/i965/brw_cfg.h   | 10 ++++++++++
>  2 files changed, 40 insertions(+), 4 deletions(-)
>

Since this algorithm just uses a single global set of if_inst, else_inst,
and endif_inst pointers, I don't think it will handle nested ifs properly.
We either need to make stacks for these new pointers, or we need to take
richer advantage of the existing cur_if, cur_else, and cur_endif stacks.


>
> diff --git a/src/mesa/drivers/dri/i965/brw_cfg.cpp
> b/src/mesa/drivers/dri/i965/brw_cfg.cpp
> index e9d2bb8..7e0e9a9 100644
> --- a/src/mesa/drivers/dri/i965/brw_cfg.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_cfg.cpp
> @@ -28,7 +28,7 @@
>  #include "brw_fs.h"
>  #include "brw_cfg.h"
>
> -/** @file brw_cfg_t.cpp
> +/** @file brw_cfg.cpp
>   *
>   * Walks the shader instructions generated and creates a set of basic
>   * blocks with successor/predecessor edges connecting them.
> @@ -52,6 +52,10 @@ bblock_t::bblock_t() :
>
>     parents.make_empty();
>     children.make_empty();
> +
> +   if_inst = NULL;
> +   else_inst = NULL;
> +   endif_inst = NULL;
>  }
>
>  void
> @@ -90,6 +94,7 @@ cfg_t::create(void *parent_mem_ctx, exec_list
> *instructions)
>     bblock_t *entry = new_block();
>     bblock_t *cur_if = NULL, *cur_else = NULL, *cur_endif = NULL;
>     bblock_t *cur_do = NULL, *cur_while = NULL;
> +   backend_instruction *if_inst = NULL, *else_inst = NULL, *endif_inst =
> NULL;
>     exec_list if_stack, else_stack, endif_stack, do_stack, while_stack;
>     bblock_t *next;
>
> @@ -121,6 +126,10 @@ cfg_t::create(void *parent_mem_ctx, exec_list
> *instructions)
>           */
>          cur_endif = new_block();
>
> +         if_inst = cur->end;
> +         else_inst = NULL;
> +         endif_inst = NULL;
> +
>          /* Set up our immediately following block, full of "then"
>           * instructions.
>           */
> @@ -134,6 +143,8 @@ cfg_t::create(void *parent_mem_ctx, exec_list
> *instructions)
>        case BRW_OPCODE_ELSE:
>          cur->add_successor(mem_ctx, cur_endif);
>
> +         else_inst = cur->end;
> +
>          next = new_block();
>          next->start = (backend_instruction *)inst->next;
>          cur_if->add_successor(mem_ctx, next);
> @@ -142,20 +153,35 @@ cfg_t::create(void *parent_mem_ctx, exec_list
> *instructions)
>          set_next_block(next);
>          break;
>
> -      case BRW_OPCODE_ENDIF:
> +      case BRW_OPCODE_ENDIF: {
>          cur_endif->start = (backend_instruction *)inst->next;
>          cur->add_successor(mem_ctx, cur_endif);
> +
> +         endif_inst = cur->end;
>          set_next_block(cur_endif);
>
> -        if (!cur_else)
> +         cur_if->if_inst = if_inst;
> +         cur_if->else_inst = else_inst;
> +         cur_if->endif_inst = endif_inst;
> +
> +        if (!cur_else) {
>             cur_if->add_successor(mem_ctx, cur_endif);
> +         } else {
> +            cur_else->if_inst = if_inst ;
> +            cur_else->else_inst = else_inst;
> +            cur_else->endif_inst = endif_inst;
> +         }
> +
> +         cur->if_inst = if_inst;
> +         cur->else_inst = else_inst;
> +         cur->endif_inst = endif_inst;
>
>          /* Pop the stack so we're in the previous if/else/endif */
>          cur_if = pop_stack(&if_stack);
>          cur_else = pop_stack(&else_stack);
>          cur_endif = pop_stack(&endif_stack);
>          break;
> -
> +      }
>        case BRW_OPCODE_DO:
>          /* Push our information onto a stack so we can recover from
>           * nested loops.
> diff --git a/src/mesa/drivers/dri/i965/brw_cfg.h
> b/src/mesa/drivers/dri/i965/brw_cfg.h
> index ec5a3a0..2ea492e 100644
> --- a/src/mesa/drivers/dri/i965/brw_cfg.h
> +++ b/src/mesa/drivers/dri/i965/brw_cfg.h
> @@ -56,6 +56,16 @@ public:
>     exec_list parents;
>     exec_list children;
>     int block_num;
> +
> +   /* If the current basic block ends in an IF, ELSE, or ENDIF
> instruction,
> +    * these pointers will hold the locations of the basic blocks ending
> in the
> +    * other associated control flow instructions.
> +    *
> +    * Otherwise they are NULL.
> +    */
> +   backend_instruction *if_inst;
> +   backend_instruction *else_inst;
> +   backend_instruction *endif_inst;
>  };
>
>  class cfg_t {
> --
> 1.8.3.2
>
>
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