[Mesa-dev] [PATCH 2/3] nir: add conditional discard optimisation
Dave Airlie
airlied at gmail.com
Thu Nov 3 09:20:16 UTC 2016
On 3 Nov. 2016 18:21, "Gustaw Smolarczyk" <wielkiegie at gmail.com> wrote:
>
> 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.
>
Yes you are right I need to add a check that there is only one instruction
in the then block.
Thanks,
Dave.
> 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
>>
>> _______________________________________________
>> mesa-dev mailing list
>> mesa-dev at lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
>
>
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