2015-08-11 20:25 GMT+02:00 Eric Anholt <e...@anholt.net>:
> We may find a cause to do more undef optimization in the future, but for
> now this fixes up things after if flattening. vc4 was handling this
> internally most of the time, but a GLB2.7 shader that did a conditional
> discard and assign gl_FragColor in the else was still emitting some extra
> code.
>
> total instructions in shared programs: 100809 -> 100795 (-0.01%)
> instructions in affected programs: 37 -> 23 (-37.84%)
> ---
> src/gallium/drivers/vc4/vc4_program.c | 1 +
> src/glsl/Makefile.sources | 1 +
> src/glsl/nir/nir.h | 2 +
> src/glsl/nir/nir_opt_undef.c | 93
> +++++++++++++++++++++++++++++++++++
> 4 files changed, 97 insertions(+)
> create mode 100644 src/glsl/nir/nir_opt_undef.c
>
> diff --git a/src/gallium/drivers/vc4/vc4_program.c
> b/src/gallium/drivers/vc4/vc4_program.c
> index e9120b7..4a3a277 100644
> --- a/src/gallium/drivers/vc4/vc4_program.c
> +++ b/src/gallium/drivers/vc4/vc4_program.c
> @@ -1627,6 +1627,7 @@ vc4_optimize_nir(struct nir_shader *s)
> progress = nir_opt_peephole_select(s) || progress;
> progress = nir_opt_algebraic(s) || progress;
> progress = nir_opt_constant_folding(s) || progress;
> + progress = nir_opt_undef(s) || progress;
> } while (progress);
> }
>
> diff --git a/src/glsl/Makefile.sources b/src/glsl/Makefile.sources
> index a0e85ed..0b77244 100644
> --- a/src/glsl/Makefile.sources
> +++ b/src/glsl/Makefile.sources
> @@ -56,6 +56,7 @@ NIR_FILES = \
> nir/nir_opt_peephole_ffma.c \
> nir/nir_opt_peephole_select.c \
> nir/nir_opt_remove_phis.c \
> + nir/nir_opt_undef.c \
> nir/nir_print.c \
> nir/nir_remove_dead_variables.c \
> nir/nir_search.c \
> diff --git a/src/glsl/nir/nir.h b/src/glsl/nir/nir.h
> index 9aae6d7..222a219 100644
> --- a/src/glsl/nir/nir.h
> +++ b/src/glsl/nir/nir.h
> @@ -1704,6 +1704,8 @@ bool nir_opt_peephole_ffma(nir_shader *shader);
>
> bool nir_opt_remove_phis(nir_shader *shader);
>
> +bool nir_opt_undef(nir_shader *shader);
> +
> void nir_sweep(nir_shader *shader);
>
> #ifdef __cplusplus
> diff --git a/src/glsl/nir/nir_opt_undef.c b/src/glsl/nir/nir_opt_undef.c
> new file mode 100644
> index 0000000..89a75c4
> --- /dev/null
> +++ b/src/glsl/nir/nir_opt_undef.c
> @@ -0,0 +1,93 @@
> +/*
> + * Copyright © 2015 Broadcom
> + *
> + * 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"
> +
> +/** @file nir_opt_undef.c
> + *
> + * Handles optimization of operations involving ssa_undef. For now, we just
> + * make sure that csels between undef and some other value just give the
> other
> + * value (on the assumption that the condition's going to be choosing the
> + * defined value). This reduces work after if flattening when each side of
> + * the if is defining a variable.
> + *
> + * Some day, we may find some use for making other operations consuming an
> + * undef arg output undef, but I don't know of any cases currently.
> + */
> +
> +static bool
> +opt_undef_alu(nir_alu_instr *instr)
> +{
> + if (instr->op != nir_op_bcsel && instr->op != nir_op_fcsel)
> + return false;
> +
> + assert(instr->dest.dest.is_ssa);
> +
> + for (int i = 1; i <= 2; i++) {
> + if (!instr->src[i].src.is_ssa)
> + continue;
> +
> + nir_instr *parent = instr->src[i].src.ssa->parent_instr;
> + if (parent->type != nir_instr_type_ssa_undef)
> + continue;
> +
> + nir_alu_src_copy(&instr->src[0], &instr->src[i == 1 ? 2 : 1],
> + ralloc_parent(instr));
> + nir_src empty_src;
> + memset(&empty_src, 0, sizeof(empty_src));
> + nir_instr_rewrite_src(&instr->instr, &instr->src[1].src, empty_src);
> + nir_instr_rewrite_src(&instr->instr, &instr->src[2].src, empty_src);
> + instr->op = nir_op_imov;
> +
> + return true;
> + }
> +
> + return false;
> +}
> +
> +static bool
> +opt_undef_block(nir_block *block, void *data)
> +{
> + bool *progress = data;
> +
> + nir_foreach_instr_safe(block, instr) {
> + if (instr->type == nir_instr_type_alu)
> + if (opt_undef_alu(nir_instr_as_alu(instr)))
> + (*progress) = true;
> + }
> +
> + return true;
> +}
> +
> +bool
> +nir_opt_undef(nir_shader *shader)
> +{
> + bool progress = false;
> +
> + nir_foreach_overload(shader, overload) {
> + if (overload->impl)
> + nir_foreach_block(overload->impl, opt_undef_block, &progress);
> + }
> +
> + return progress;
> +}
> --
> 2.1.4
>
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> mesa-dev@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/mesa-dev
For future reference there is a nice little summary of how one
might want to deal with undef inputs to different operations at[1]
at aproximately line 1300. This is for SCCP, in the LLVM compiler,
but I guess an expansion to this pass would not be to different.
Just thought I'd mention it since I've been looking at it a bit =)
[1]
https://github.com/llvm-mirror/llvm/blob/master/lib/Transforms/Scalar/SCCP.cpp
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