nir: Add an expression matching framework

This framework provides a simple way to do simple search-and-replace
operations on NIR code.  The nir_search.h header provides four simple data
structures for representing expressions:  nir_value and four subtypes:
nir_variable, nir_constant, and nir_expression.  An expression tree can
then be represented by nesting these data structures as needed.  The
nir_replace_instr function takes an instruction, an expression, and a
value; if the instruction matches the expression, it is replaced with a new
chain of instructions to generate the given replacement value.  The
framework keeps track of swizzles on sources and automatically generates
the currect swizzles for the replacement value.

Reviewed-by: Connor Abbott <[email protected]>

1 files changed, 364 insertions, 0 deletions

diff --git a/src/glsl/nir/nir_search.c b/src/glsl/nir/nir_search.c
new file mode 100644
index 00000000000..3930795a041
--- /dev/null
+++ b/src/glsl/nir/nir_search.c
@@ -0,0 +1,364 @@
+/*
+ * 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_search.h"
+
+struct match_state {
+   unsigned variables_seen;
+   nir_alu_src variables[NIR_SEARCH_MAX_VARIABLES];
+};
+
+static bool
+is_commutative_binop(nir_op op)
+{
+   switch (op) {
+   case nir_op_fadd:
+   case nir_op_iadd:
+   case nir_op_fmul:
+   case nir_op_imul:
+   case nir_op_imul_high:
+   case nir_op_umul_high:
+   case nir_op_feq:
+   case nir_op_fne:
+   case nir_op_ieq:
+   case nir_op_ine:
+   case nir_op_fand:
+   case nir_op_for:
+   case nir_op_fxor:
+   case nir_op_iand:
+   case nir_op_ior:
+   case nir_op_ixor:
+   case nir_op_fmin:
+   case nir_op_fmax:
+   case nir_op_imin:
+   case nir_op_imax:
+   case nir_op_umin:
+   case nir_op_umax:
+      return true;
+   default:
+      return false;
+   }
+}
+
+static bool
+match_expression(const nir_search_expression *expr, nir_alu_instr *instr,
+                 unsigned num_components, const uint8_t *swizzle,
+                 struct match_state *state);
+
+static const uint8_t identity_swizzle[] = { 0, 1, 2, 3 };
+
+static bool
+match_value(const nir_search_value *value, nir_alu_instr *instr, unsigned src,
+            unsigned num_components, const uint8_t *swizzle,
+            struct match_state *state)
+{
+   uint8_t new_swizzle[4];
+
+   for (int i = 0; i < num_components; ++i)
+      new_swizzle[i] = instr->src[src].swizzle[swizzle[i]];
+
+   switch (value->type) {
+   case nir_search_value_expression:
+      if (!instr->src[src].src.is_ssa)
+         return false;
+
+      if (instr->src[src].src.ssa->parent_instr->type != nir_instr_type_alu)
+         return false;
+
+      return match_expression(nir_search_value_as_expression(value),
+                              nir_instr_as_alu(instr->src[src].src.ssa->parent_instr),
+                              num_components, new_swizzle, state);
+
+   case nir_search_value_variable: {
+      nir_search_variable *var = nir_search_value_as_variable(value);
+
+      if (state->variables_seen & (1 << var->variable)) {
+         if (!nir_srcs_equal(state->variables[var->variable].src,
+                             instr->src[src].src))
+            return false;
+
+         assert(!instr->src[src].abs && !instr->src[src].negate);
+
+         for (int i = 0; i < num_components; ++i) {
+            if (state->variables[var->variable].swizzle[i] != new_swizzle[i])
+               return false;
+         }
+
+         return true;
+      } else {
+         state->variables_seen |= (1 << var->variable);
+         state->variables[var->variable].src = instr->src[src].src;
+         state->variables[var->variable].abs = false;
+         state->variables[var->variable].negate = false;
+
+         for (int i = 0; i < 4; ++i) {
+            if (i < num_components)
+               state->variables[var->variable].swizzle[i] = new_swizzle[i];
+            else
+               state->variables[var->variable].swizzle[i] = 0;
+         }
+
+         return true;
+      }
+   }
+
+   case nir_search_value_constant: {
+      nir_search_constant *const_val = nir_search_value_as_constant(value);
+
+      if (!instr->src[src].src.is_ssa)
+         return false;
+
+      if (instr->src[src].src.ssa->parent_instr->type != nir_instr_type_load_const)
+         return false;
+
+      nir_load_const_instr *load =
+         nir_instr_as_load_const(instr->src[src].src.ssa->parent_instr);
+
+      switch (nir_op_infos[instr->op].input_types[src]) {
+      case nir_type_float:
+         for (unsigned i = 0; i < num_components; ++i) {
+            if (load->value.f[new_swizzle[i]] != const_val->data.f)
+               return false;
+         }
+         return true;
+      case nir_type_int:
+      case nir_type_unsigned:
+      case nir_type_bool:
+         for (unsigned i = 0; i < num_components; ++i) {
+            if (load->value.i[new_swizzle[i]] != const_val->data.i)
+               return false;
+         }
+         return true;
+      default:
+         unreachable("Invalid alu source type");
+      }
+   }
+
+   default:
+      unreachable("Invalid search value type");
+   }
+}
+
+static bool
+match_expression(const nir_search_expression *expr, nir_alu_instr *instr,
+                 unsigned num_components, const uint8_t *swizzle,
+                 struct match_state *state)
+{
+   if (instr->op != expr->opcode)
+      return false;
+
+   assert(!instr->dest.saturate);
+   assert(nir_op_infos[instr->op].num_inputs > 0);
+
+   /* If we have an explicitly sized destination, we can only handle the
+    * identity swizzle.  While dot(vec3(a, b, c).zxy) is a valid
+    * expression, we don't have the information right now to propagate that
+    * swizzle through.  We can only properly propagate swizzles if the
+    * instruction is vectorized.
+    */
+   if (nir_op_infos[instr->op].output_size != 0) {
+      for (unsigned i = 0; i < num_components; i++) {
+         if (swizzle[i] != i)
+            return false;
+      }
+   }
+
+   bool matched = true;
+   for (unsigned i = 0; i < nir_op_infos[instr->op].num_inputs; i++) {
+      /* If the source is an explicitly sized source, then we need to reset
+       * both the number of components and the swizzle.
+       */
+      if (nir_op_infos[instr->op].input_sizes[i] != 0) {
+         num_components = nir_op_infos[instr->op].input_sizes[i];
+         swizzle = identity_swizzle;
+      }
+
+      if (!match_value(expr->srcs[i], instr, i, num_components,
+                       swizzle, state)) {
+         matched = false;
+         break;
+      }
+   }
+
+   if (matched)
+      return true;
+
+   if (is_commutative_binop(instr->op)) {
+      if (!match_value(expr->srcs[0], instr, 1, num_components,
+                       swizzle, state))
+         return false;
+
+      return match_value(expr->srcs[1], instr, 0, num_components,
+                         swizzle, state);
+   } else {
+      return false;
+   }
+}
+
+static nir_alu_src
+construct_value(const nir_search_value *value, nir_alu_type type,
+                unsigned num_components, struct match_state *state,
+                nir_instr *instr, void *mem_ctx)
+{
+   switch (value->type) {
+   case nir_search_value_expression: {
+      const nir_search_expression *expr = nir_search_value_as_expression(value);
+
+      if (nir_op_infos[expr->opcode].output_size != 0)
+         num_components = nir_op_infos[expr->opcode].output_size;
+
+      nir_alu_instr *alu = nir_alu_instr_create(mem_ctx, expr->opcode);
+      alu->dest.dest.is_ssa = true;
+      nir_ssa_def_init(&alu->instr, &alu->dest.dest.ssa, num_components, NULL);
+      alu->dest.write_mask = (1 << num_components) - 1;
+      alu->dest.saturate = false;
+
+      for (unsigned i = 0; i < nir_op_infos[expr->opcode].num_inputs; i++) {
+         /* If the source is an explicitly sized source, then we need to reset
+          * the number of components to match.
+          */
+         if (nir_op_infos[alu->op].input_sizes[i] != 0)
+            num_components = nir_op_infos[alu->op].input_sizes[i];
+
+         alu->src[i] = construct_value(expr->srcs[i],
+                                       nir_op_infos[alu->op].input_types[i],
+                                       num_components,
+                                       state, instr, mem_ctx);
+      }
+
+      nir_instr_insert_before(instr, &alu->instr);
+
+      nir_alu_src val = {
+         .src.is_ssa = true,
+         .src.ssa = &alu->dest.dest.ssa,
+         .negate = false,
+         .abs = false,
+         .swizzle = { 0, 1, 2, 3 }
+      };
+
+      return val;
+   }
+
+   case nir_search_value_variable: {
+      const nir_search_variable *var = nir_search_value_as_variable(value);
+      assert(state->variables_seen & (1 << var->variable));
+
+      nir_alu_src val = state->variables[var->variable];
+      val.src = nir_src_copy(val.src, mem_ctx);
+
+      return val;
+   }
+
+   case nir_search_value_constant: {
+      const nir_search_constant *c = nir_search_value_as_constant(value);
+      nir_load_const_instr *load = nir_load_const_instr_create(mem_ctx);
+      load->dest.is_ssa = true;
+      nir_ssa_def_init(&load->instr, &load->dest.ssa, 1, NULL);
+
+      switch (type) {
+      case nir_type_float:
+         load->dest.ssa.name = ralloc_asprintf(mem_ctx, "%f", c->data.f);
+         load->value.f[0] = c->data.f;
+         break;
+      case nir_type_int:
+         load->dest.ssa.name = ralloc_asprintf(mem_ctx, "%d", c->data.i);
+         load->value.i[0] = c->data.i;
+         break;
+      case nir_type_unsigned:
+      case nir_type_bool:
+         load->value.u[0] = c->data.u;
+         break;
+      default:
+         unreachable("Invalid alu source type");
+      }
+
+      nir_instr_insert_before(instr, &load->instr);
+
+      nir_alu_src val = {
+         .src.is_ssa = true,
+         .src.ssa = &load->dest.ssa,
+         .negate = false,
+         .abs = false,
+         .swizzle = { 0, 0, 0, 0 } /* Splatted scalar */
+      };
+
+      return val;
+   }
+
+   default:
+      unreachable("Invalid search value type");
+   }
+}
+
+nir_alu_instr *
+nir_replace_instr(nir_alu_instr *instr, const nir_search_expression *search,
+                  const nir_search_value *replace, void *mem_ctx)
+{
+   uint8_t swizzle[4] = { 0, 0, 0, 0 };
+
+   for (unsigned i = 0; i < instr->dest.dest.ssa.num_components; ++i)
+      swizzle[i] = i;
+
+   assert(instr->dest.dest.is_ssa);
+
+   struct match_state state;
+   state.variables_seen = 0;
+
+   if (!match_expression(search, instr, instr->dest.dest.ssa.num_components,
+                         swizzle, &state))
+      return NULL;
+
+   /* 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.
+    */
+   nir_alu_instr *mov = nir_alu_instr_create(mem_ctx, nir_op_imov);
+   mov->dest.write_mask = instr->dest.write_mask;
+   mov->dest.dest.is_ssa = true;
+   nir_ssa_def_init(&mov->instr, &mov->dest.dest.ssa,
+                    instr->dest.dest.ssa.num_components, NULL);
+
+   mov->src[0] = construct_value(replace, nir_op_infos[instr->op].output_type,
+                                 instr->dest.dest.ssa.num_components, &state,
+                                 &instr->instr, mem_ctx);
+   nir_instr_insert_before(&instr->instr, &mov->instr);
+
+   nir_src replace_src = {
+      .is_ssa = true,
+      .ssa = &mov->dest.dest.ssa,
+   };
+
+   nir_ssa_def_rewrite_uses(&instr->dest.dest.ssa, replace_src, mem_ctx);
+
+   /* We know this one has no more uses because we just rewrote them all,
+    * so we can remove it.  The rest of the matched expression, however, we
+    * don't know so much about.  We'll just let dead code clean them up.
+    */
+   nir_instr_remove(&instr->instr);
+
+   return mov;
+}