i965: Add a NIR analysis pass for determining when a boolean resolve is needed

v2: Fix the spelling of analyze and re-arrange code for better readability
    as per Connor's comments.
v3: Make the naming of things more consistent and add a pile of comments
v4: Stop trying to avoid vectors

Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>

1 files changed, 268 insertions, 0 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_nir_analyze_boolean_resolves.c b/src/mesa/drivers/dri/i965/brw_nir_analyze_boolean_resolves.c
new file mode 100644
index 0000000..3a27cf1
--- /dev/null
+++ b/src/mesa/drivers/dri/i965/brw_nir_analyze_boolean_resolves.c
@@ -0,0 +1,268 @@
+/*
+ * Copyright © 2015 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 <jason@jlekstrand.net>
+ */
+
+#include "brw_nir.h"
+
+/*
+ * This file implements an analysis pass that determines when we have to do
+ * a boolean resolve on Gen <= 5.  Instructions that need a boolean resolve
+ * will have the booleans portion of the instr->pass_flags field set to
+ * BRW_NIR_BOOLEAN_NEEDS_RESOLVE.
+ */
+
+
+/** Returns the resolve status for the given source
+ *
+ * If the source has a parent instruction then the resolve status is the
+ * status of the parent instruction.  If the source does not have a parent
+ * instruction then we don't know so we return NON_BOOLEAN.
+ */
+static uint8_t
+get_resolve_status_for_src(nir_src *src)
+{
+   nir_instr *src_instr;
+   if (src->is_ssa) {
+      src_instr = src->ssa->parent_instr;
+   } else {
+      src_instr = src->reg.reg->parent_instr;
+   }
+
+   if (src_instr) {
+      uint8_t resolve_status = src_instr->pass_flags & BRW_NIR_BOOLEAN_MASK;
+
+      /* If the source instruction needs resolve, then from the perspective
+       * of the user, it's a true boolean.
+       */
+      if (resolve_status == BRW_NIR_BOOLEAN_NEEDS_RESOLVE)
+         resolve_status = BRW_NIR_BOOLEAN_NO_RESOLVE;
+      return resolve_status;
+   } else {
+      return BRW_NIR_NON_BOOLEAN;
+   }
+}
+
+/** Marks the given source as needing a resolve
+ *
+ * If the given source corresponds to an unresolved boolean it marks it as
+ * needing a resolve.  Otherwise, we leave it alone.
+ */
+static bool
+src_mark_needs_resolve(nir_src *src, void *void_state)
+{
+   nir_instr *src_instr;
+   if (src->is_ssa) {
+      src_instr = src->ssa->parent_instr;
+   } else {
+      src_instr = src->reg.reg->parent_instr;
+   }
+
+   if (src_instr) {
+      uint8_t resolve_status = src_instr->pass_flags & BRW_NIR_BOOLEAN_MASK;
+
+      /* If the source instruction is unresolved, then mark it as needing
+       * to be resolved.
+       */
+      if (resolve_status == BRW_NIR_BOOLEAN_UNRESOLVED) {
+         src_instr->pass_flags &= ~BRW_NIR_BOOLEAN_MASK;
+         src_instr->pass_flags |= BRW_NIR_BOOLEAN_NEEDS_RESOLVE;
+      }
+
+   }
+
+   return true;
+}
+
+static bool
+analyze_boolean_resolves_block(nir_block *block, void *void_state)
+{
+   nir_foreach_instr(block, instr) {
+      switch (instr->type) {
+      case nir_instr_type_alu: {
+         /* For ALU instructions, the resolve status is handled in a
+          * three-step process.
+          *
+          * 1) Look at the instruction type and sources and determine if it
+          *    can be left unresolved.
+          *
+          * 2) Look at the destination and see if we have to resolve
+          *    anyway.  (This is the case if this instruction is not the
+          *    only instruction writing to a given register.)
+          *
+          * 3) If the instruction has a resolve status other than
+          *    BOOL_UNRESOLVED or BOOL_NEEDS_RESOLVE then we walk through
+          *    the sources and ensure that they are also resolved.  This
+          *    ensures that we don't end up with any stray unresolved
+          *    booleans going into ADDs or something like that.
+          */
+
+         uint8_t resolve_status;
+         nir_alu_instr *alu = nir_instr_as_alu(instr);
+         switch (alu->op) {
+         case nir_op_flt:
+         case nir_op_ilt:
+         case nir_op_ult:
+         case nir_op_fge:
+         case nir_op_ige:
+         case nir_op_uge:
+         case nir_op_feq:
+         case nir_op_ieq:
+         case nir_op_fne:
+         case nir_op_ine:
+         case nir_op_f2b:
+         case nir_op_i2b:
+            /* This instruction will turn into a CMP when we actually emit
+             * so the result will have to be resolved before it can be used.
+             */
+            resolve_status = BRW_NIR_BOOLEAN_UNRESOLVED;
+
+            /* Even though the destination is allowed to be left unresolved,
+             * the sources are treated as regular integers or floats so
+             * they need to be resolved.
+             */
+            nir_foreach_src(instr, src_mark_needs_resolve, NULL);
+            break;
+
+         case nir_op_imov:
+         case nir_op_inot:
+            /* This is a single-source instruction.  Just copy the resolve
+             * status from the source.
+             */
+            resolve_status = get_resolve_status_for_src(&alu->src[0].src);
+            break;
+
+         case nir_op_iand:
+         case nir_op_ior:
+         case nir_op_ixor: {
+            uint8_t src0_status = get_resolve_status_for_src(&alu->src[0].src);
+            uint8_t src1_status = get_resolve_status_for_src(&alu->src[1].src);
+
+            if (src0_status == src1_status) {
+               resolve_status = src0_status;
+            } else if (src0_status == BRW_NIR_NON_BOOLEAN ||
+                       src1_status == BRW_NIR_NON_BOOLEAN) {
+               /* If one of the sources is a non-boolean then the whole
+                * thing is a non-boolean.
+                */
+               resolve_status = BRW_NIR_NON_BOOLEAN;
+            } else {
+               /* At this point one of them is a true boolean and one is a
+                * boolean that needs a resolve.  We could either resolve the
+                * unresolved source or we could resolve here.  If we resolve
+                * the unresolved source then we get two resolves for the price
+                * of one.  Just set this one to BOOLEAN_NO_RESOLVE and we'll
+                * let the code below force a resolve on the unresolved source.
+                */
+               resolve_status = BRW_NIR_BOOLEAN_NO_RESOLVE;
+            }
+            break;
+         }
+
+         default:
+            resolve_status = BRW_NIR_NON_BOOLEAN;
+         }
+
+         /* If the destination is SSA-like, go ahead allow unresolved booleans.
+          * If the destination register doesn't have a well-defined parent_instr
+          * we need to resolve immediately.
+          */
+         if (alu->dest.dest.reg.reg->parent_instr == NULL &&
+             resolve_status == BRW_NIR_BOOLEAN_UNRESOLVED) {
+            resolve_status = BRW_NIR_BOOLEAN_NEEDS_RESOLVE;
+         }
+
+         instr->pass_flags = (instr->pass_flags & ~BRW_NIR_BOOLEAN_MASK) |
+                             resolve_status;
+
+         /* Finally, resolve sources if it's needed */
+         switch (resolve_status) {
+         case BRW_NIR_BOOLEAN_NEEDS_RESOLVE:
+         case BRW_NIR_BOOLEAN_UNRESOLVED:
+            /* This instruction is either unresolved or we're doing the
+             * resolve here; leave the sources alone.
+             */
+            break;
+
+         case BRW_NIR_BOOLEAN_NO_RESOLVE:
+         case BRW_NIR_NON_BOOLEAN:
+            nir_foreach_src(instr, src_mark_needs_resolve, NULL);
+            break;
+
+         default:
+            unreachable("Invalid boolean flag");
+         }
+
+         break;
+      }
+
+      case nir_instr_type_load_const: {
+         nir_load_const_instr *load = nir_instr_as_load_const(instr);
+
+         /* For load_const instructions, it's a boolean exactly when it holds
+          * one of the values NIR_TRUE or NIR_FALSE.
+          *
+          * Since load_const instructions don't have any sources, we don't
+          * have to worry about resolving them.
+          */
+         instr->pass_flags &= ~BRW_NIR_BOOLEAN_MASK;
+         if (load->value.u[0] == NIR_TRUE || load->value.u[0] == NIR_FALSE) {
+            instr->pass_flags |= BRW_NIR_BOOLEAN_NO_RESOLVE;
+         } else {
+            instr->pass_flags |= BRW_NIR_NON_BOOLEAN;
+         }
+         continue;
+      }
+
+      default:
+         /* Everything else is an unknown non-boolean value and needs to
+          * have all sources resolved.
+          */
+         instr->pass_flags = (instr->pass_flags & ~BRW_NIR_BOOLEAN_MASK) |
+                             BRW_NIR_NON_BOOLEAN;
+         nir_foreach_src(instr, src_mark_needs_resolve, NULL);
+         continue;
+      }
+   }
+
+   nir_if *following_if = nir_block_get_following_if(block);
+   if (following_if)
+      src_mark_needs_resolve(&following_if->condition, NULL);
+
+   return true;
+}
+
+static void
+analyze_boolean_resolves_impl(nir_function_impl *impl)
+{
+   nir_foreach_block(impl, analyze_boolean_resolves_block, NULL);
+}
+
+void
+brw_nir_analyze_boolean_resolves(nir_shader *shader)
+{
+   nir_foreach_overload(shader, overload)
+      if (overload->impl)
+         analyze_boolean_resolves_impl(overload->impl);
+}