intel/fs: Rework fs_inst::is_copy_payload() into multiple classification helpers.

This reworks the current fs_inst::is_copy_payload() method into a
number of classification helpers with well-defined semantics.  This
will be useful later on in order to optimize LOAD_PAYLOAD instructions
more aggressively in cases where we can determine it's safe to do so.

The closest equivalent of the present fs_inst::is_copy_payload()
method is the is_coalescing_payload() helper introduced here.

No functional nor shader-db changes.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/intel/compiler/brw_fs.cpp

@@ -427,34 +427,6 @@ fs_inst::has_source_and_destination_hazard() const
    }
 }
 
-bool
-fs_inst::is_copy_payload(const brw::simple_allocator &grf_alloc) const
-{
-   if (this->opcode != SHADER_OPCODE_LOAD_PAYLOAD)
-      return false;
-
-   fs_reg reg = this->src[0];
-   if (reg.file != VGRF || reg.offset != 0 || reg.stride != 1)
-      return false;
-
-   if (grf_alloc.sizes[reg.nr] * REG_SIZE != this->size_written)
-      return false;
-
-   for (int i = 0; i < this->sources; i++) {
-      reg.type = this->src[i].type;
-      if (!this->src[i].equals(reg))
-         return false;
-
-      if (i < this->header_size) {
-         reg.offset += REG_SIZE;
-      } else {
-         reg = horiz_offset(reg, this->exec_size);
-      }
-   }
-
-   return true;
-}
-
 bool
 fs_inst::can_do_source_mods(const struct gen_device_info *devinfo) const
 {

src/intel/compiler/brw_fs_cse.cpp

@@ -105,7 +105,7 @@ is_expression(const fs_visitor *v, const fs_inst *const inst)
    case SHADER_OPCODE_COS:
       return inst->mlen < 2;
    case SHADER_OPCODE_LOAD_PAYLOAD:
-      return !inst->is_copy_payload(v->alloc);
+      return !is_coalescing_payload(v->alloc, inst);
    default:
       return inst->is_send_from_grf() && !inst->has_side_effects() &&
          !inst->is_volatile();

src/intel/compiler/brw_fs_register_coalesce.cpp

@@ -86,7 +86,7 @@ is_coalesce_candidate(const fs_visitor *v, const fs_inst *inst)
       return false;
 
    if (inst->opcode == SHADER_OPCODE_LOAD_PAYLOAD) {
-      if (!inst->is_copy_payload(v->alloc)) {
+      if (!is_coalescing_payload(v->alloc, inst)) {
          return false;
       }
    }

src/intel/compiler/brw_ir_fs.h

@@ -350,7 +350,6 @@ public:
    bool is_send_from_grf() const;
    bool is_payload(unsigned arg) const;
    bool is_partial_write() const;
-   bool is_copy_payload(const brw::simple_allocator &grf_alloc) const;
    unsigned components_read(unsigned i) const;
    unsigned size_read(int arg) const;
    bool can_do_source_mods(const struct gen_device_info *devinfo) const;
@@ -570,4 +569,103 @@ has_dst_aligned_region_restriction(const gen_device_info *devinfo,
       return false;
 }
 
+/**
+ * Return whether the LOAD_PAYLOAD instruction is a plain copy of bits from
+ * the specified register file into a VGRF.
+ *
+ * This implies identity register regions without any source-destination
+ * overlap, but otherwise has no implications on the location of sources and
+ * destination in the register file: Gathering any number of portions from
+ * multiple virtual registers in any order is allowed.
+ */
+inline bool
+is_copy_payload(brw_reg_file file, const fs_inst *inst)
+{
+   if (inst->opcode != SHADER_OPCODE_LOAD_PAYLOAD ||
+       inst->is_partial_write() || inst->saturate ||
+       inst->dst.file != VGRF)
+      return false;
+
+   for (unsigned i = 0; i < inst->sources; i++) {
+      if (inst->src[i].file != file ||
+          inst->src[i].abs || inst->src[i].negate)
+         return false;
+
+      if (!inst->src[i].is_contiguous())
+         return false;
+
+      if (regions_overlap(inst->dst, inst->size_written,
+                          inst->src[i], inst->size_read(i)))
+         return false;
+   }
+
+   return true;
+}
+
+/**
+ * Like is_copy_payload(), but the instruction is required to copy a single
+ * contiguous block of registers from the given register file into the
+ * destination without any reordering.
+ */
+inline bool
+is_identity_payload(brw_reg_file file, const fs_inst *inst) {
+   if (is_copy_payload(file, inst)) {
+      fs_reg reg = inst->src[0];
+
+      for (unsigned i = 0; i < inst->sources; i++) {
+         reg.type = inst->src[i].type;
+         if (!inst->src[i].equals(reg))
+            return false;
+
+         reg = byte_offset(reg, inst->size_read(i));
+      }
+
+      return true;
+   } else {
+      return false;
+   }
+}
+
+/**
+ * Like is_copy_payload(), but the instruction is required to source data from
+ * at least two disjoint VGRFs.
+ *
+ * This doesn't necessarily rule out the elimination of this instruction
+ * through register coalescing, but due to limitations of the register
+ * coalesce pass it might be impossible to do so directly until a later stage,
+ * when the LOAD_PAYLOAD instruction is unrolled into a sequence of MOV
+ * instructions.
+ */
+inline bool
+is_multi_copy_payload(const fs_inst *inst) {
+   if (is_copy_payload(VGRF, inst)) {
+      for (unsigned i = 0; i < inst->sources; i++) {
+            if (inst->src[i].nr != inst->src[0].nr)
+               return true;
+      }
+   }
+
+   return false;
+}
+
+/**
+ * Like is_identity_payload(), but the instruction is required to copy the
+ * whole contents of a single VGRF into the destination.
+ *
+ * This means that there is a good chance that the instruction will be
+ * eliminated through register coalescing, but it's neither a necessary nor a
+ * sufficient condition for that to happen -- E.g. consider the case where
+ * source and destination registers diverge due to other instructions in the
+ * program overwriting part of their contents, which isn't something we can
+ * predict up front based on a cheap strictly local test of the copy
+ * instruction.
+ */
+inline bool
+is_coalescing_payload(const brw::simple_allocator &alloc, const fs_inst *inst)
+{
+   return is_identity_payload(VGRF, inst) &&
+          inst->src[0].offset == 0 &&
+          alloc.sizes[inst->src[0].nr] * REG_SIZE == inst->size_written;
+}
+
 #endif