[Mesa-dev] [PATCH 01/11] i965/vs: Add support for splitting virtual GRFs.

[Kenneth Graunke]

On 10/04/2012 04:07 PM, Eric Anholt wrote:
> This should improve our ability to register allocate without spilling.
> Unfortuantely, due to the live variable analysis being ignorant of loops, we
> still have register allocation failures on some programs.
> ---
>   src/mesa/drivers/dri/i965/brw_vec4.cpp      |   54 +++++++++++++++++++++++++++
>   src/mesa/drivers/dri/i965/brw_vec4.h        |    1 +
>   src/mesa/drivers/dri/i965/brw_vec4_emit.cpp |    1 +
>   3 files changed, 56 insertions(+)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_vec4.cpp b/src/mesa/drivers/dri/i965/brw_vec4.cpp
> index 2941729..fbd49ca 100644
> --- a/src/mesa/drivers/dri/i965/brw_vec4.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_vec4.cpp
> @@ -865,4 +865,58 @@ vec4_visitor::opt_compute_to_mrf()
>      return progress;
>   }
>
> +/**
> + * Splits virtual GRFs requesting more than one contiguous physical register.
> + *
> + * Unlike in the FS visitor, we have no SEND messages that return more than 1
> + * register.  We also don't do any array access in register space, which would
> + * have required contiguous physical registers.
> + */

It would be nice to mention what the VS /does/ have that occupies VGRFs 
of size > 1.  Structures and matrices?

Otherwise, this looks good.
Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>

> +void
> +vec4_visitor::split_virtual_grfs()
> +{
> +   int num_vars = this->virtual_grf_count;
> +   int new_virtual_grf[num_vars];
> +
> +   memset(new_virtual_grf, 0, sizeof(new_virtual_grf));
> +
> +   /* Allocate new space for split regs.  Note that the virtual
> +    * numbers will be contiguous.
> +    */
> +   for (int i = 0; i < num_vars; i++) {
> +      if (this->virtual_grf_sizes[i] == 1)
> +         continue;
> +
> +      new_virtual_grf[i] = virtual_grf_alloc(1);
> +      for (int j = 2; j < this->virtual_grf_sizes[i]; j++) {
> +         int reg = virtual_grf_alloc(1);
> +         assert(reg == new_virtual_grf[i] + j - 1);
> +         (void) reg;
> +      }
> +      this->virtual_grf_sizes[i] = 1;
> +   }
> +
> +   foreach_list(node, &this->instructions) {
> +      vec4_instruction *inst = (vec4_instruction *)node;
> +
> +      if (inst->dst.file == GRF &&
> +	  new_virtual_grf[inst->dst.reg] &&
> +	  inst->dst.reg_offset != 0) {
> +	 inst->dst.reg = (new_virtual_grf[inst->dst.reg] +
> +			  inst->dst.reg_offset - 1);
> +	 inst->dst.reg_offset = 0;
> +      }
> +      for (int i = 0; i < 3; i++) {
> +	 if (inst->src[i].file == GRF &&
> +	     new_virtual_grf[inst->src[i].reg] &&
> +	     inst->src[i].reg_offset != 0) {
> +	    inst->src[i].reg = (new_virtual_grf[inst->src[i].reg] +
> +				inst->src[i].reg_offset - 1);
> +	    inst->src[i].reg_offset = 0;
> +	 }
> +      }
> +   }
> +   this->live_intervals_valid = false;
> +}
> +
>   } /* namespace brw */
> diff --git a/src/mesa/drivers/dri/i965/brw_vec4.h b/src/mesa/drivers/dri/i965/brw_vec4.h
> index dce3c89..4fdede3 100644
> --- a/src/mesa/drivers/dri/i965/brw_vec4.h
> +++ b/src/mesa/drivers/dri/i965/brw_vec4.h
> @@ -323,6 +323,7 @@ public:
>      void split_uniform_registers();
>      void pack_uniform_registers();
>      void calculate_live_intervals();
> +   void split_virtual_grfs();
>      bool dead_code_eliminate();
>      bool virtual_grf_interferes(int a, int b);
>      bool opt_copy_propagation();
> diff --git a/src/mesa/drivers/dri/i965/brw_vec4_emit.cpp b/src/mesa/drivers/dri/i965/brw_vec4_emit.cpp
> index 5a941d9..479b0a6 100644
> --- a/src/mesa/drivers/dri/i965/brw_vec4_emit.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_vec4_emit.cpp
> @@ -794,6 +794,7 @@ vec4_visitor::run()
>      move_uniform_array_access_to_pull_constants();
>      pack_uniform_registers();
>      move_push_constants_to_pull_constants();
> +   split_virtual_grfs();
>
>      bool progress;
>      do {
>