Mesa (master): nir: Skip emitting no-op movs from the builder.
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Fri Oct 4 19:34:39 UTC 2019
Module: Mesa
Branch: master
Commit: 7025dbe794b53b030ae0a3cb55217ea831a810d9
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=7025dbe794b53b030ae0a3cb55217ea831a810d9
Author: Eric Anholt <eric at anholt.net>
Date: Mon Sep 16 14:34:20 2019 -0700
nir: Skip emitting no-op movs from the builder.
Having passes generate these is just making more work for copy
propagation (and thus probably calling more optimization passes)
later. Noticed while trying to debug nir_opt_algebraic()
top-to-bottom having O(n^2) behavior due to not finding new matches in
replacement code.
Reviewed-by: Ian Romanick <ian.d.romainck at intel.com>
Reviewed-by: Connor Abbott <cwabbott0 at gmail.com>
---
src/compiler/nir/nir_builder.h | 10 ++++++++++
src/compiler/nir/nir_search.c | 5 ++---
2 files changed, 12 insertions(+), 3 deletions(-)
diff --git a/src/compiler/nir/nir_builder.h b/src/compiler/nir/nir_builder.h
index 0f300aef155..cad0e133cbf 100644
--- a/src/compiler/nir/nir_builder.h
+++ b/src/compiler/nir/nir_builder.h
@@ -458,6 +458,16 @@ static inline nir_ssa_def *
nir_mov_alu(nir_builder *build, nir_alu_src src, unsigned num_components)
{
assert(!src.abs && !src.negate);
+ if (src.src.is_ssa && src.src.ssa->num_components == num_components) {
+ bool any_swizzles = false;
+ for (unsigned i = 0; i < num_components; i++) {
+ if (src.swizzle[i] != i)
+ any_swizzles = true;
+ }
+ if (!any_swizzles)
+ return src.src.ssa;
+ }
+
nir_alu_instr *mov = nir_alu_instr_create(build->shader, nir_op_mov);
nir_ssa_dest_init(&mov->instr, &mov->dest.dest, num_components,
nir_src_bit_size(src.src), NULL);
diff --git a/src/compiler/nir/nir_search.c b/src/compiler/nir/nir_search.c
index eb7249cfdec..de5a8d25ada 100644
--- a/src/compiler/nir/nir_search.c
+++ b/src/compiler/nir/nir_search.c
@@ -673,9 +673,8 @@ nir_replace_instr(nir_builder *build, nir_alu_instr *instr,
instr->dest.dest.ssa.bit_size,
&state, &instr->instr);
- /* Inserting a mov may be unnecessary. However, it's much easier to
- * simply let copy propagation clean this up than to try to go through
- * and rewrite swizzles ourselves.
+ /* Note that NIR builder will elide the MOV if it's a no-op, which may
+ * allow more work to be done in a single pass through algebraic.
*/
nir_ssa_def *ssa_val =
nir_mov_alu(build, val, instr->dest.dest.ssa.num_components);
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