nir/opt_peephole_select: handle speculative ubo loads

Some platforms may be able to speculate ubo loads safely.

Signed-off-by: Christian Gmeiner <cgmeiner@igalia.com>
Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8299>

src/compiler/nir/meson.build

@@ -358,6 +358,7 @@ if with_tests
         'tests/mod_analysis_tests.cpp',
         'tests/negative_equal_tests.cpp',
         'tests/opt_if_tests.cpp',
+        'tests/opt_peephole_select.cpp',
         'tests/opt_shrink_vectors_tests.cpp',
         'tests/serialize_tests.cpp',
         'tests/range_analysis_tests.cpp',

src/compiler/nir/nir_opt_peephole_select.c

@@ -128,6 +128,14 @@ block_check_for_allowed_instrs(nir_block *block, unsigned *count,
             break;
          }
 
+         case nir_intrinsic_load_ubo:
+         case nir_intrinsic_load_ubo_vec4:
+            if (!indirect_load_ok && !nir_src_is_const(intrin->src[1]))
+               return false;
+            if (!(nir_intrinsic_access(intrin) & ACCESS_CAN_SPECULATE))
+               return false;
+            break;
+
          case nir_intrinsic_load_uniform:
          case nir_intrinsic_load_preamble:
          case nir_intrinsic_load_helper_invocation:

src/compiler/nir/tests/opt_peephole_select.cpp

@@ -0,0 +1,153 @@
+/*
+ * Copyright (c) 2020 Etnaviv Project
+ *
+ * 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, sub license,
+ * 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 NON-INFRINGEMENT. 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:
+ *    Christian Gmeiner <christian.gmeiner@gmail.com>
+ */
+
+#include <gtest/gtest.h>
+#include "nir.h"
+#include "nir_builder.h"
+
+class nir_opt_peephole_select_test : public ::testing::Test {
+protected:
+   nir_opt_peephole_select_test();
+   ~nir_opt_peephole_select_test();
+
+   nir_builder bld;
+};
+
+nir_opt_peephole_select_test::nir_opt_peephole_select_test()
+{
+   glsl_type_singleton_init_or_ref();
+
+   static const nir_shader_compiler_options options = { };
+   bld = nir_builder_init_simple_shader(MESA_SHADER_VERTEX, &options, "peephole test");
+}
+
+nir_opt_peephole_select_test::~nir_opt_peephole_select_test()
+{
+   ralloc_free(bld.shader);
+   glsl_type_singleton_decref();
+}
+
+TEST_F(nir_opt_peephole_select_test, opt_load_ubo_no_speculate)
+{
+   /* Tests that opt_peephole_select does not optimize ubo loads:
+    *
+    * impl main {
+    *     block b0:  // preds:
+    *     32    %0 = load_const (0x00000001)
+    *     32    %1 = load_const (0x00000002)
+    *     32    %2 = load_const (0x0000000a = 10)
+    *     1     %3 = ieq %0 (0x1), %1 (0x2)
+    *                // succs: b1 b2
+    *     if %3 {
+    *         block b1:  // preds: b0
+    *         32    %4 = @load_ubo (%0 (0x1), %2 (0xa)) (access=0, align_mul=16, align_offset=0, range_base=16, range=16)
+    *                    // succs: b3
+    *     } else {
+    *         block b2:  // preds: b0
+    *         32    %5 = @load_ubo (%0 (0x1), %2 (0xa)) (access=0, align_mul=16, align_offset=0, range_base=16, range=16)
+    *                    // succs: b3
+    *     }
+    *     block b3:  // preds: b1 b2, succs: b4
+    *     block b4:
+    * }
+    */
+   nir_function *main = nir_shader_get_function_for_name(bld.shader, "main");
+
+   nir_def *one = nir_imm_int(&bld, 1);
+   nir_def *two = nir_imm_int(&bld, 2);
+   nir_def *ten = nir_imm_int(&bld, 10);
+
+   nir_def *cmp_result = nir_ieq(&bld, one, two);
+   nir_push_if(&bld, cmp_result);
+
+   nir_load_ubo(&bld, 1, 32, one, ten, (gl_access_qualifier)0, 16, 0, 16, 16);
+
+   nir_push_else(&bld, NULL);
+
+   nir_load_ubo(&bld, 1, 32, one, ten, (gl_access_qualifier)0, 16, 0, 16, 16);
+
+   nir_pop_if(&bld, NULL);
+
+   nir_index_blocks(main->impl);
+   EXPECT_EQ(main->impl->num_blocks, 4);
+
+   ASSERT_FALSE(nir_opt_peephole_select(bld.shader, 16, true, true));
+   nir_validate_shader(bld.shader, NULL);
+
+   nir_index_blocks(main->impl);
+   EXPECT_EQ(main->impl->num_blocks, 4);
+}
+
+TEST_F(nir_opt_peephole_select_test, opt_load_ubo_speculate)
+{
+   /* Tests that opt_peephole_select correctly optimizes speculative ubo loads:
+    *
+    * impl main {
+    *    block b0:  // preds:
+    *    32    %0 = load_const (0x00000001)
+    *    32    %1 = load_const (0x00000002)
+    *    32    %2 = load_const (0x0000000a = 10)
+    *    1     %3 = ieq %0 (0x1), %1 (0x2)
+    *               // succs: b1 b2
+    *    if %3 {
+    *        block b1:  // preds: b0
+    *        32    %4 = @load_ubo (%0 (0x1), %2 (0xa)) (access=4096, align_mul=16, align_offset=0, range_base=16, range=16)
+    *                   // succs: b3
+    *    } else {
+    *        block b2:  // preds: b0
+    *        32    %5 = @load_ubo (%0 (0x1), %2 (0xa)) (access=4096, align_mul=16, align_offset=0, range_base=16, range=16)
+    *                   // succs: b3
+    *    }
+    *    block b3:  // preds: b1 b2, succs: b4
+    *    block b4:
+    *}
+    */
+   nir_function *main = nir_shader_get_function_for_name(bld.shader, "main");
+
+   nir_def *one = nir_imm_int(&bld, 1);
+   nir_def *two = nir_imm_int(&bld, 2);
+   nir_def *ten = nir_imm_int(&bld, 10);
+
+   nir_def *cmp_result = nir_ieq(&bld, one, two);
+   nir_push_if(&bld, cmp_result);
+
+   nir_load_ubo(&bld, 1, 32, one, ten, (gl_access_qualifier)ACCESS_CAN_SPECULATE, 16, 0, 16, 16);
+
+   nir_push_else(&bld, NULL);
+
+   nir_load_ubo(&bld, 1, 32, one, ten, (gl_access_qualifier)ACCESS_CAN_SPECULATE, 16, 0, 16, 16);
+
+   nir_pop_if(&bld, NULL);
+
+   nir_index_blocks(main->impl);
+   EXPECT_EQ(main->impl->num_blocks, 4);
+
+   ASSERT_TRUE(nir_opt_peephole_select(bld.shader, 16, true, true));
+   nir_validate_shader(bld.shader, NULL);
+
+   nir_index_blocks(main->impl);
+   EXPECT_EQ(main->impl->num_blocks, 1);
+}