[Mesa-dev] [PATCH 2/3] nir: add conditional discard optimisation
Gustaw Smolarczyk
wielkiegie at gmail.com
Thu Nov 3 08:21:51 UTC 2016
I am not really that much familiar with nir, so I apologize if what I write
below is wrong.
What if we had something like:
a = 0;
if (x) {
discard_if(y);
a = 1;
}
Then if (x && !y), we must not discard and both at the same time set a to
1. Your transformation would probably change it to:
a = 0;
discard_if(x && y);
Which is incorrect.
I think you have to ensure (if the intrinsic is discard_if) that discard_if
is the only instruction inside the then block. Or just remove the intrinsic
from the then block and leave the rest of the if alone.
Regards,
Gustaw
2016-11-03 4:28 GMT+01:00 Dave Airlie <airlied at gmail.com>:
> From: Dave Airlie <airlied at redhat.com>
>
> This is ported from GLSL and converts
>
> if (cond)
> discard;
>
> into
> discard_if(cond);
>
> This removes a block, but also is needed by radv
> to workaround a bug in the LLVM backend.
>
> v2: handle if (a) discard_if(b) (nha)
> cleanup and drop pointless loop (Matt)
> make sure there are no dependent phis (Eric)
>
> Signed-off-by: Dave Airlie <airlied at redhat.com>
> ---
> src/compiler/Makefile.sources | 1 +
> src/compiler/nir/nir.h | 2 +
> src/compiler/nir/nir_opt_conditional_discard.c | 124
> +++++++++++++++++++++++++
> 3 files changed, 127 insertions(+)
> create mode 100644 src/compiler/nir/nir_opt_conditional_discard.c
>
> diff --git a/src/compiler/Makefile.sources b/src/compiler/Makefile.sources
> index 669c499..b710cbd 100644
> --- a/src/compiler/Makefile.sources
> +++ b/src/compiler/Makefile.sources
> @@ -228,6 +228,7 @@ NIR_FILES = \
> nir/nir_metadata.c \
> nir/nir_move_vec_src_uses_to_dest.c \
> nir/nir_normalize_cubemap_coords.c \
> + nir/nir_opt_conditional_discard.c \
> nir/nir_opt_constant_folding.c \
> nir/nir_opt_copy_propagate.c \
> nir/nir_opt_cse.c \
> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
> index 9264763..2a77139 100644
> --- a/src/compiler/nir/nir.h
> +++ b/src/compiler/nir/nir.h
> @@ -2531,6 +2531,8 @@ bool nir_opt_remove_phis(nir_shader *shader);
>
> bool nir_opt_undef(nir_shader *shader);
>
> +bool nir_opt_conditional_discard(nir_shader *shader);
> +
> void nir_sweep(nir_shader *shader);
>
> nir_intrinsic_op nir_intrinsic_from_system_value(gl_system_value val);
> diff --git a/src/compiler/nir/nir_opt_conditional_discard.c
> b/src/compiler/nir/nir_opt_conditional_discard.c
> new file mode 100644
> index 0000000..2259a14
> --- /dev/null
> +++ b/src/compiler/nir/nir_opt_conditional_discard.c
> @@ -0,0 +1,124 @@
> +/*
> + * Copyright © 2016 Red Hat
> + *
> + * Permission is hereby granted, free of charge, to any person obtaining a
> + * copy of this software and associated documentation files (the
> "Software"),
> + * to deal in the Software without restriction, including without
> limitation
> + * the rights to use, copy, modify, merge, publish, distribute,
> sublicense,
> + * and/or sell copies of the Software, and to permit persons to whom the
> + * Software is furnished to do so, subject to the following conditions:
> + *
> + * The above copyright notice and this permission notice (including the
> next
> + * paragraph) shall be included in all copies or substantial portions of
> the
> + * Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
> EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
> MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
> SHALL
> + * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
> OTHER
> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
> + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
> DEALINGS
> + * IN THE SOFTWARE.
> + */
> +
> +#include "nir.h"
> +#include "nir_builder.h"
> +
> +/** @file nir_opt_conditional_discard.c
> + *
> + * Handles optimization of lowering if (cond) discard to discard_if(cond).
> + */
> +
> +static bool
> +nir_opt_conditional_discard_block(nir_block *block, void *mem_ctx)
> +{
> + nir_builder bld;
> +
> + if (nir_cf_node_is_first(&block->cf_node))
> + return false;
> +
> + nir_cf_node *prev_node = nir_cf_node_prev(&block->cf_node);
> + if (prev_node->type != nir_cf_node_if)
> + return false;
> +
> + nir_if *if_stmt = nir_cf_node_as_if(prev_node);
> + nir_block *then_block = nir_if_first_then_block(if_stmt);
> + nir_block *else_block = nir_if_first_else_block(if_stmt);
> +
> + /* check there is only one else block and it is empty */
> + if (nir_if_last_else_block(if_stmt) != else_block)
> + return false;
> + if (!exec_list_is_empty(&else_block->instr_list))
> + return false;
> +
> + /* check there is only one then block and it has instructions in it */
> + if (nir_if_last_then_block(if_stmt) != then_block)
> + return false;
> + if (exec_list_is_empty(&then_block->instr_list))
> + return false;
> +
> + /*
> + * make sure no subsequent phi nodes point at this if.
> + */
> + nir_block *after = nir_cf_node_as_block(nir_cf_
> node_next(&if_stmt->cf_node));
> + nir_foreach_instr_safe(instr, after) {
> + if (instr->type != nir_instr_type_phi)
> + break;
> + nir_phi_instr *phi = nir_instr_as_phi(instr);
> +
> + nir_foreach_phi_src(phi_src, phi) {
> + if (phi_src->pred == then_block ||
> + phi_src->pred == else_block)
> + return false;
> + }
> + }
> +
> + /* Get the first instruction in the then block and confirm it is
> + * a discard or a discard_if
> + */
> + nir_instr *instr = nir_block_first_instr(then_block);
> + if (instr->type != nir_instr_type_intrinsic)
> + return false;
> +
> + nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
> + if (intrin->intrinsic != nir_intrinsic_discard &&
> + intrin->intrinsic != nir_intrinsic_discard_if)
> + return false;
> +
> + nir_src cond;
> +
> + nir_builder_init(&bld, mem_ctx);
> +
> + if (intrin->intrinsic == nir_intrinsic_discard)
> + cond = if_stmt->condition;
> + else
> + cond = nir_src_for_ssa(nir_iand(&bld,
> + nir_ssa_for_src(&bld,
> if_stmt->condition, 1),
> + nir_ssa_for_src(&bld, intrin->src[0],
> 1)));
> +
> + nir_intrinsic_instr *discard_if =
> + nir_intrinsic_instr_create(mem_ctx, nir_intrinsic_discard_if);
> + nir_src_copy(&discard_if->src[0], &cond, discard_if);
> +
> + nir_instr_insert_before_cf(prev_node, &discard_if->instr);
> + nir_instr_remove(&intrin->instr);
> + nir_cf_node_remove(&if_stmt->cf_node);
> +
> + return true;
> +}
> +
> +bool
> +nir_opt_conditional_discard(nir_shader *shader)
> +{
> + bool progress = false;
> +
> + nir_foreach_function(function, shader) {
> + if (function->impl) {
> + void *mem_ctx = ralloc_parent(function->impl);
> + nir_foreach_block_safe(block, function->impl) {
> + progress |= nir_opt_conditional_discard_block(block,
> mem_ctx);
> + }
> + }
> + }
> + return progress;
> +}
> --
> 2.7.4
>
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