[Mesa-dev] [PATCH v2 15/20] i965/vec4: consider subregister offset in live variables

[Francisco Jerez]

Samuel Iglesias Gonsálvez <siglesias at igalia.com> writes:

> From: "Juan A. Suarez Romero" <jasuarez at igalia.com>
>
> Take in account the offset value when getting the var from register.
>
> This is required when dealing with an operation that writes half of the
> register (like one d2x in IVB/BYT, which uses exec_size == 4).
>
> Note that for live analysis variables we need to stick to per-GRF
> analysis. In this case, we use var_from_reg() with GRF precision.

This looks bogus to me.  If the specified register had a non-zero
sub-GRF offset and we weren't taking it into account we have a bug.  The
vec4 liveness analysis pass keeps track of dataflow with 32-bit
granularity these days so we want the variable index computation to be
done with the same precision.

> ---
>  src/mesa/drivers/dri/i965/brw_vec4_live_variables.cpp | 12 ++++++++----
>  src/mesa/drivers/dri/i965/brw_vec4_live_variables.h   | 10 ++++++----
>  2 files changed, 14 insertions(+), 8 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_vec4_live_variables.cpp b/src/mesa/drivers/dri/i965/brw_vec4_live_variables.cpp
> index 73f658cd8fa..54ebd0994ee 100644
> --- a/src/mesa/drivers/dri/i965/brw_vec4_live_variables.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_vec4_live_variables.cpp
> @@ -78,7 +78,8 @@ vec4_live_variables::setup_def_use()
>  	    if (inst->src[i].file == VGRF) {
>                 for (unsigned j = 0; j < DIV_ROUND_UP(inst->size_read(i), 16); j++) {
>                    for (int c = 0; c < 4; c++) {
> -                     const unsigned v = var_from_reg(alloc, inst->src[i], c, j);
> +                     const unsigned v =
> +                        var_from_reg(alloc, inst->src[i], c, j, false);
>                       if (!BITSET_TEST(bd->def, v))
>                          BITSET_SET(bd->use, v);
>                    }
> @@ -101,7 +102,8 @@ vec4_live_variables::setup_def_use()
>              for (unsigned i = 0; i < DIV_ROUND_UP(inst->size_written, 16); i++) {
>                 for (int c = 0; c < 4; c++) {
>                    if (inst->dst.writemask & (1 << c)) {
> -                     const unsigned v = var_from_reg(alloc, inst->dst, c, i);
> +                     const unsigned v =
> +                        var_from_reg(alloc, inst->dst, c, i, false);
>                       if (!BITSET_TEST(bd->use, v))
>                          BITSET_SET(bd->def, v);
>                    }
> @@ -257,7 +259,8 @@ vec4_visitor::calculate_live_intervals()
>  	 if (inst->src[i].file == VGRF) {
>              for (unsigned j = 0; j < DIV_ROUND_UP(inst->size_read(i), 16); j++) {
>                 for (int c = 0; c < 4; c++) {
> -                  const unsigned v = var_from_reg(alloc, inst->src[i], c, j);
> +                  const unsigned v =
> +                     var_from_reg(alloc, inst->src[i], c, j, false);
>                    start[v] = MIN2(start[v], ip);
>                    end[v] = ip;
>                 }
> @@ -269,7 +272,8 @@ vec4_visitor::calculate_live_intervals()
>           for (unsigned i = 0; i < DIV_ROUND_UP(inst->size_written, 16); i++) {
>              for (int c = 0; c < 4; c++) {
>                 if (inst->dst.writemask & (1 << c)) {
> -                  const unsigned v = var_from_reg(alloc, inst->dst, c, i);
> +                  const unsigned v =
> +                     var_from_reg(alloc, inst->dst, c, i, false);
>                    start[v] = MIN2(start[v], ip);
>                    end[v] = ip;
>                 }
> diff --git a/src/mesa/drivers/dri/i965/brw_vec4_live_variables.h b/src/mesa/drivers/dri/i965/brw_vec4_live_variables.h
> index 8807c453743..9c505d15f1f 100644
> --- a/src/mesa/drivers/dri/i965/brw_vec4_live_variables.h
> +++ b/src/mesa/drivers/dri/i965/brw_vec4_live_variables.h
> @@ -83,13 +83,14 @@ protected:
>   */
>  inline unsigned
>  var_from_reg(const simple_allocator &alloc, const src_reg &reg,
> -             unsigned c = 0, unsigned k = 0)
> +             unsigned c = 0, unsigned k = 0, bool subreg_precision = true)
>  {
>     assert(reg.file == VGRF && reg.nr < alloc.count && c < 4);
>     const unsigned csize = DIV_ROUND_UP(type_sz(reg.type), 4);
>     unsigned result =
>        8 * (alloc.offsets[reg.nr] + reg.offset / REG_SIZE) +
> -      (BRW_GET_SWZ(reg.swizzle, c) + k / csize * 4) * csize + k % csize;
> +      (BRW_GET_SWZ(reg.swizzle, c) + k / csize * 4) * csize + k % csize +
> +      (subreg_precision ? (reg.offset % REG_SIZE) / type_sz(reg.type) : 0);
>     /* Do not exceed the limit for this register */
>     assert(result < 8 * (alloc.offsets[reg.nr] + alloc.sizes[reg.nr]));
>     return result;
> @@ -97,13 +98,14 @@ var_from_reg(const simple_allocator &alloc, const src_reg &reg,
>  
>  inline unsigned
>  var_from_reg(const simple_allocator &alloc, const dst_reg &reg,
> -             unsigned c = 0, unsigned k = 0)
> +             unsigned c = 0, unsigned k = 0, bool subreg_precision = true)
>  {
>     assert(reg.file == VGRF && reg.nr < alloc.count && c < 4);
>     const unsigned csize = DIV_ROUND_UP(type_sz(reg.type), 4);
>     unsigned result =
>        8 * (alloc.offsets[reg.nr] + reg.offset / REG_SIZE) +
> -      (c + k / csize * 4) * csize + k % csize;
> +      (c + k / csize * 4) * csize + k % csize +
> +      (subreg_precision ? (reg.offset % REG_SIZE) / type_sz(reg.type) : 0);
>     /* Do not exceed the limit for this register */
>     assert(result < 8 * (alloc.offsets[reg.nr] + alloc.sizes[reg.nr]));
>     return result;
> -- 
> 2.11.0
>
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> mesa-dev at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
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