pan/bi: Validate the live set starts empty

Otherwise there is an uninitialized read, and the register allocation
will fail. (In the sense of failing a precondition. This manifests as
synthetic interference leading to higher register pressure and useless
moves. The allocation itself is ok, but it indicates a real bug.)

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12130>

src/panfrost/bifrost/bi_validate.c

@@ -0,0 +1,78 @@
+/*
+ * Copyright (C) 2021 Collabora, Ltd.
+ *
+ * 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 "compiler.h"
+#include "util/u_memory.h"
+
+/* Validatation doesn't make sense in release builds */
+#ifndef NDEBUG
+
+/* Validate that all sources are initialized in all read components. This is
+ * required for correct register allocation. We check a weaker condition, that
+ * all sources that are read are written at some point (equivalently, the live
+ * set is empty at the start of the program). TODO: Strengthen */
+
+bool
+bi_validate_initialization(bi_context *ctx)
+{
+        bool success = true;
+
+        /* Calculate the live set */
+        bi_block *entry = bi_entry_block(ctx);
+        unsigned temp_count = bi_max_temp(ctx);
+        bi_invalidate_liveness(ctx);
+        bi_compute_liveness(ctx);
+
+        /* Validate that the live set is indeed empty */
+        for (unsigned i = 0; i < temp_count; ++i) {
+                if (entry->live_in[i] == 0) continue;
+
+                fprintf(stderr, "%s%u\n", (i & PAN_IS_REG) ? "r" : "", i >> 1);
+                success = false;
+        }
+
+        return success;
+}
+
+void
+bi_validate(bi_context *ctx, const char *after)
+{
+        bool fail = false;
+
+        if (bifrost_debug & BIFROST_DBG_NOVALIDATE)
+                return;
+
+        if (!bi_validate_initialization(ctx)) {
+                fprintf(stderr, "Uninitialized data read after %s\n", after);
+                fail = true;
+        }
+
+        /* TODO: Validate more invariants */
+
+        if (fail) {
+                bi_print_shader(ctx, stderr);
+                exit(1);
+        }
+}
+
+#endif /* NDEBUG */

src/panfrost/bifrost/bifrost.h

@@ -37,6 +37,7 @@
 #define BIFROST_DBG_INTERNAL    0x0010
 #define BIFROST_DBG_NOSCHED     0x0020
 #define BIFROST_DBG_INORDER     0x0040
+#define BIFROST_DBG_NOVALIDATE  0x0080
 
 extern int bifrost_debug;
 

src/panfrost/bifrost/bifrost_compile.c

@@ -45,6 +45,7 @@ static const struct debug_named_value bifrost_debug_options[] = {
         {"internal",  BIFROST_DBG_INTERNAL,	"Dump even internal shaders"},
         {"nosched",   BIFROST_DBG_NOSCHED, 	"Force trivial bundling"},
         {"inorder",   BIFROST_DBG_INORDER, 	"Force in-order bundling"},
+        {"novalidate",BIFROST_DBG_NOVALIDATE,   "Skip IR validation"},
         DEBUG_NAMED_VALUE_END
 };
 
@@ -3659,6 +3660,8 @@ bifrost_compile_shader_nir(nir_shader *nir,
                 block->name = block_source_count++;
         }
 
+        bi_validate(ctx, "NIR -> BIR");
+
         /* If the shader doesn't write any colour or depth outputs, it may
          * still need an ATEST at the very end! */
         bool need_dummy_atest =
@@ -3674,6 +3677,7 @@ bifrost_compile_shader_nir(nir_shader *nir,
 
         /* Runs before constant folding */
         bi_lower_swizzle(ctx);
+        bi_validate(ctx, "Early lowering");
 
         /* Runs before copy prop */
         bi_opt_push_ubo(ctx);
@@ -3685,6 +3689,7 @@ bifrost_compile_shader_nir(nir_shader *nir,
         bi_opt_dead_code_eliminate(ctx);
         bi_opt_cse(ctx);
         bi_opt_dead_code_eliminate(ctx);
+        bi_validate(ctx, "Optimization passes");
 
         bi_foreach_block(ctx, block) {
                 bi_lower_branch(block);
@@ -3698,6 +3703,7 @@ bifrost_compile_shader_nir(nir_shader *nir,
          * skip bit is a function of only the data flow graph and is invariant
          * under valid scheduling. */
         bi_analyze_helper_requirements(ctx);
+        bi_validate(ctx, "Late lowering");
 
         bi_register_allocate(ctx);
         bi_opt_post_ra(ctx);

src/panfrost/bifrost/compiler.h

@@ -910,6 +910,14 @@ bool bi_reads_zero(bi_instr *ins);
 bool bi_reads_temps(bi_instr *ins, unsigned src);
 bool bi_reads_t(bi_instr *ins, unsigned src);
 
+#ifndef NDEBUG
+bool bi_validate_initialization(bi_context *ctx);
+void bi_validate(bi_context *ctx, const char *after_str);
+#else
+static inline bool bi_validate_initialization(UNUSED bi_context *ctx) { return true; }
+static inline void bi_validate(UNUSED bi_context *ctx, UNUSED const char *after_str) { return; }
+#endif
+
 uint32_t bi_fold_constant(bi_instr *I, bool *unsupported);
 void bi_opt_constant_fold(bi_context *ctx);
 

src/panfrost/bifrost/meson.build

@@ -38,6 +38,7 @@ libpanfrost_bifrost_files = files(
   'bi_ra.c',
   'bi_schedule.c',
   'bi_scoreboard.c',
+  'bi_validate.c',
   'bir.c',
   'bifrost_compile.c',
 )