nir: Add a dedicated ffma peephole optimization

i965/nir: Use the dedicated ffma peephole

total instructions in shared programs: 4418748 -> 4394618 (-0.55%)
instructions in affected programs:     1292790 -> 1268660 (-1.87%)
helped:                                5999
HURT:                                  457
GAINED:                                4
LOST:                                  9

Reviewed-by: Matt Turner <[email protected]>

3 files changed, 223 insertions, 0 deletions

diff --git a/src/glsl/Makefile.sources b/src/glsl/Makefile.sources
index fa5d991b5a0..b56fa2608ea 100644
--- a/src/glsl/Makefile.sources
+++ b/src/glsl/Makefile.sources
@@ -48,6 +48,7 @@ NIR_FILES = \
 	nir/nir_opt_dce.c \
 	nir/nir_opt_gcm.c \
 	nir/nir_opt_global_to_local.c \
+	nir/nir_opt_peephole_ffma.c \
 	nir/nir_opt_peephole_select.c \
 	nir/nir_opt_remove_phis.c \
 	nir/nir_print.c \
diff --git a/src/glsl/nir/nir_opt_peephole_ffma.c b/src/glsl/nir/nir_opt_peephole_ffma.c
new file mode 100644
index 00000000000..1ba4ac2b195
--- /dev/null
+++ b/src/glsl/nir/nir_opt_peephole_ffma.c
@@ -0,0 +1,220 @@
+/*
+ * Copyright © 2014 Intel Corporation
+ *
+ * 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.
+ *
+ * Authors:
+ *    Jason Ekstrand ([email protected])
+ *
+ */
+
+#include "nir.h"
+
+/*
+ * Implements a small peephole optimization that looks for a multiply that
+ * is only ever used in an add and replaces both with an fma.
+ */
+
+struct peephole_ffma_state {
+   void *mem_ctx;
+   nir_function_impl *impl;
+   bool progress;
+};
+
+static nir_alu_instr *
+get_mul_for_src(nir_alu_src *src, uint8_t swizzle[4], bool *negate, bool *abs)
+{
+   assert(src->src.is_ssa && !src->abs && !src->negate);
+
+   nir_instr *instr = src->src.ssa->parent_instr;
+   if (instr->type != nir_instr_type_alu)
+      return NULL;
+
+   nir_alu_instr *alu = nir_instr_as_alu(instr);
+   switch (alu->op) {
+   case nir_op_imov:
+   case nir_op_fmov:
+      alu = get_mul_for_src(&alu->src[0], swizzle, negate, abs);
+      break;
+
+   case nir_op_fneg:
+      alu = get_mul_for_src(&alu->src[0], swizzle, negate, abs);
+      *negate = !*negate;
+      break;
+
+   case nir_op_fabs:
+      alu = get_mul_for_src(&alu->src[0], swizzle, negate, abs);
+      *negate = false;
+      *abs = true;
+      break;
+
+   case nir_op_fmul:
+      break;
+
+   default:
+      return NULL;
+   }
+
+   if (!alu)
+      return NULL;
+
+   for (unsigned i = 0; i < 4; i++) {
+      if (!(alu->dest.write_mask & (1 << i)))
+         break;
+
+      swizzle[i] = swizzle[src->swizzle[i]];
+   }
+
+   return alu;
+}
+
+static bool
+nir_opt_peephole_ffma_block(nir_block *block, void *void_state)
+{
+   struct peephole_ffma_state *state = void_state;
+
+   nir_foreach_instr_safe(block, instr) {
+      if (instr->type != nir_instr_type_alu)
+         continue;
+
+      nir_alu_instr *add = nir_instr_as_alu(instr);
+      if (add->op != nir_op_fadd)
+         continue;
+
+      /* TODO: Maybe bail if this expression is considered "precise"? */
+
+      assert(add->src[0].src.is_ssa && add->src[1].src.is_ssa);
+
+      /* This, is the case a + a.  We would rather handle this with an
+       * algebraic reduction than fuse it.  Also, we want to only fuse
+       * things where the multiply is used only once and, in this case,
+       * it would be used twice by the same instruction.
+       */
+      if (add->src[0].src.ssa == add->src[1].src.ssa)
+         continue;
+
+      nir_alu_instr *mul;
+      uint8_t add_mul_src, swizzle[4];
+      bool negate, abs;
+      for (add_mul_src = 0; add_mul_src < 2; add_mul_src++) {
+         for (unsigned i = 0; i < 4; i++)
+            swizzle[i] = i;
+
+         negate = false;
+         abs = false;
+
+         mul = get_mul_for_src(&add->src[add_mul_src], swizzle, &negate, &abs);
+
+         if (mul != NULL)
+            break;
+      }
+
+      if (mul == NULL)
+         continue;
+
+      nir_ssa_def *mul_src[2];
+      mul_src[0] = mul->src[0].src.ssa;
+      mul_src[1] = mul->src[1].src.ssa;
+
+      if (abs) {
+         for (unsigned i = 0; i < 2; i++) {
+            nir_alu_instr *abs = nir_alu_instr_create(state->mem_ctx,
+                                                      nir_op_fabs);
+            abs->src[0].src = nir_src_for_ssa(mul_src[i]);
+            nir_ssa_dest_init(&abs->instr, &abs->dest.dest,
+                              mul_src[i]->num_components, NULL);
+            abs->dest.write_mask = (1 << mul_src[i]->num_components) - 1;
+            nir_instr_insert_before(&add->instr, &abs->instr);
+            mul_src[i] = &abs->dest.dest.ssa;
+         }
+      }
+
+      if (negate) {
+         nir_alu_instr *neg = nir_alu_instr_create(state->mem_ctx,
+                                                   nir_op_fneg);
+         neg->src[0].src = nir_src_for_ssa(mul_src[0]);
+         nir_ssa_dest_init(&neg->instr, &neg->dest.dest,
+                           mul_src[0]->num_components, NULL);
+         neg->dest.write_mask = (1 << mul_src[0]->num_components) - 1;
+         nir_instr_insert_before(&add->instr, &neg->instr);
+         mul_src[0] = &neg->dest.dest.ssa;
+      }
+
+      nir_alu_instr *ffma = nir_alu_instr_create(state->mem_ctx, nir_op_ffma);
+      ffma->dest.saturate = add->dest.saturate;
+      ffma->dest.write_mask = add->dest.write_mask;
+
+      for (unsigned i = 0; i < 2; i++) {
+         ffma->src[i].src = nir_src_for_ssa(mul_src[i]);
+         for (unsigned j = 0; j < add->dest.dest.ssa.num_components; j++)
+            ffma->src[i].swizzle[j] = mul->src[i].swizzle[swizzle[j]];
+      }
+      nir_alu_src_copy(&ffma->src[2], &add->src[1 - add_mul_src],
+                       state->mem_ctx);
+
+      assert(add->dest.dest.is_ssa);
+
+      nir_ssa_dest_init(&ffma->instr, &ffma->dest.dest,
+                        add->dest.dest.ssa.num_components,
+                        add->dest.dest.ssa.name);
+      nir_ssa_def_rewrite_uses(&add->dest.dest.ssa,
+                               nir_src_for_ssa(&ffma->dest.dest.ssa),
+                               state->mem_ctx);
+
+      nir_instr_insert_before(&add->instr, &ffma->instr);
+      assert(add->dest.dest.ssa.uses->entries == 0);
+      nir_instr_remove(&add->instr);
+
+      state->progress = true;
+   }
+
+   return true;
+}
+
+static bool
+nir_opt_peephole_ffma_impl(nir_function_impl *impl)
+{
+   struct peephole_ffma_state state;
+
+   state.mem_ctx = ralloc_parent(impl);
+   state.impl = impl;
+   state.progress = false;
+
+   nir_foreach_block(impl, nir_opt_peephole_ffma_block, &state);
+
+   if (state.progress)
+      nir_metadata_preserve(impl, nir_metadata_block_index |
+                                  nir_metadata_dominance);
+
+   return state.progress;
+}
+
+bool
+nir_opt_peephole_ffma(nir_shader *shader)
+{
+   bool progress = false;
+
+   nir_foreach_overload(shader, overload) {
+      if (overload->impl)
+         progress |= nir_opt_peephole_ffma_impl(overload->impl);
+   }
+
+   return progress;
+}
diff --git a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
index 204e713ea55..4f4b74620fe 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
@@ -52,6 +52,8 @@ nir_optimize(nir_shader *nir)
       nir_validate_shader(nir);
       progress |= nir_opt_algebraic(nir);
       nir_validate_shader(nir);
+      progress |= nir_opt_peephole_ffma(nir);
+      nir_validate_shader(nir);
       progress |= nir_opt_constant_folding(nir);
       nir_validate_shader(nir);
       progress |= nir_opt_remove_phis(nir);