agx: Add a trivial register allocator

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Acked-by: Jason Ekstrand <jason@jlekstrand.net>
Acked-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10582>

src/asahi/compiler/agx_compile.c

@@ -500,6 +500,11 @@ agx_compile_shader_nir(nir_shader *nir,
    agx_foreach_block(ctx, block)
       block->name = block_source_count++;
 
+   if (agx_debug & AGX_DBG_SHADERS && !skip_internal)
+      agx_print_shader(ctx, stdout);
+
+   agx_ra(ctx);
+
    if (agx_debug & AGX_DBG_SHADERS && !skip_internal)
       agx_print_shader(ctx, stdout);
 

src/asahi/compiler/agx_compiler.h

@@ -547,5 +547,6 @@ agx_builder_insert(agx_cursor *cursor, agx_instr *I)
 void agx_print_instr(agx_instr *I, FILE *fp);
 void agx_print_block(agx_block *block, FILE *fp);
 void agx_print_shader(agx_context *ctx, FILE *fp);
+void agx_ra(agx_context *ctx);
 
 #endif

src/asahi/compiler/agx_register_allocate.c

@@ -0,0 +1,103 @@
+/*
+ * Copyright (C) 2021 Alyssa Rosenzweig <alyssa@rosenzweig.io>
+ *
+ * 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.
+ */
+
+#include "agx_compiler.h"
+#include "agx_builder.h"
+
+/* Trivial register allocator that never frees anything.
+ *
+ * TODO: Write a real register allocator.
+ * TODO: Handle phi nodes.
+ */
+
+void
+agx_ra(agx_context *ctx)
+{
+   unsigned *alloc = calloc(ctx->alloc, sizeof(unsigned));
+   unsigned usage = 6*2;
+
+   agx_foreach_instr_global_safe(ctx, ins) {
+      /* Lower away RA pseudo-instructions */
+      if (ins->op == AGX_OPCODE_P_COMBINE) {
+         /* TODO: Optimize out the moves! */
+         unsigned components = 0;
+
+         for (unsigned i = 0; i < 4; ++i) {
+            if (!agx_is_null(ins->src[i]))
+               components = i + 1;
+         }
+
+         unsigned size = ins->dest[0].size == AGX_SIZE_32 ? 2 : 1;
+         if (size == 2 && usage & 1) usage++;
+         unsigned base = usage;
+         assert(ins->dest[0].type == AGX_INDEX_NORMAL);
+         alloc[ins->dest[0].value] = base;
+         usage += (components * size);
+
+         /* Move the sources */
+         agx_builder b = agx_init_builder(ctx, agx_after_instr(ins));
+
+         for (unsigned i = 0; i < 4; ++i) {
+            if (agx_is_null(ins->src[i])) continue;
+            assert(ins->src[0].type == AGX_INDEX_NORMAL);
+            agx_mov_to(&b, agx_register(base + (i * size), ins->dest[0].size),
+                  agx_register(alloc[ins->src[i].value], ins->src[0].size));
+         }
+
+         /* We've lowered away, delete the old */
+         agx_remove_instruction(ins);
+         continue;
+      } else if (ins->op == AGX_OPCODE_P_EXTRACT) {
+         assert(ins->dest[0].type == AGX_INDEX_NORMAL);
+         assert(ins->src[0].type == AGX_INDEX_NORMAL);
+         assert(ins->dest[0].size == ins->src[0].size);
+
+         unsigned size = ins->dest[0].size == AGX_SIZE_32 ? 2 : 1;
+         alloc[ins->dest[0].value] = alloc[ins->src[0].value] + (size * ins->imm);
+         agx_remove_instruction(ins);
+         continue;
+      }
+
+      agx_foreach_src(ins, s) {
+         if (ins->src[s].type == AGX_INDEX_NORMAL) {
+            unsigned v = alloc[ins->src[s].value];
+            ins->src[s] = agx_replace_index(ins->src[s], agx_register(v, ins->src[s].size));
+         }
+      }
+
+      agx_foreach_dest(ins, d) {
+         if (ins->dest[d].type == AGX_INDEX_NORMAL) {
+            unsigned size = ins->dest[d].size == AGX_SIZE_32 ? 2 : 1;
+            if (size == 2 && usage & 1) usage++;
+            unsigned v = usage;
+            unsigned comps = (ins->op == AGX_OPCODE_LD_VARY || ins->op == AGX_OPCODE_DEVICE_LOAD || ins->op == AGX_OPCODE_TEXTURE_SAMPLE) ? 4 : 1; // todo systematic
+            usage += comps * size;
+            alloc[ins->dest[d].value] = v;
+            ins->dest[d] = agx_replace_index(ins->dest[d], agx_register(v, ins->dest[d].size));
+         }
+      }
+   }
+
+   assert(usage < 256 && "dummy RA");
+   free(alloc);
+}

src/asahi/compiler/meson.build

@@ -22,6 +22,7 @@
 libasahi_agx_files = files(
   'agx_compile.c',
   'agx_print.c',
+  'agx_register_allocate.c',
 )
 
 agx_opcodes_h = custom_target(