nir: Add a nir_instr_remove that recursively removes dead code.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11628>

src/compiler/nir/meson.build

@@ -392,6 +392,19 @@ if with_tests
     suite : ['compiler', 'nir'],
   )
 
+  test(
+    'nir_core',
+    executable(
+      'nir_core_test',
+      files('tests/core_tests.cpp'),
+      cpp_args : [cpp_msvc_compat_args],
+      gnu_symbol_visibility : 'hidden',
+      include_directories : [inc_include, inc_src, inc_mapi, inc_mesa, inc_gallium, inc_gallium_aux],
+      dependencies : [dep_thread, idep_gtest, idep_nir, idep_mesautil],
+    ),
+    suite : ['compiler', 'nir'],
+  )
+
   test(
     'nir_vars',
     executable(

src/compiler/nir/nir.c

@@ -28,6 +28,7 @@
 #include "nir.h"
 #include "nir_builder.h"
 #include "nir_control_flow_private.h"
+#include "nir_worklist.h"
 #include "util/half_float.h"
 #include <limits.h>
 #include <assert.h>
@@ -1069,6 +1070,75 @@ void nir_instr_remove_v(nir_instr *instr)
    }
 }
 
+static bool nir_instr_remove_and_dce_live_cb(nir_ssa_def *def, void *state)
+{
+   bool *live = state;
+
+   if (!nir_ssa_def_is_unused(def)) {
+      *live = true;
+      return false;
+   } else {
+      return true;
+   }
+}
+
+static bool nir_instr_remove_and_dce_is_live(nir_instr *instr)
+{
+   /* Note: don't have to worry about jumps because they don't have dests to
+    * become unused.
+    */
+   if (instr->type == nir_instr_type_intrinsic) {
+      nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
+      const nir_intrinsic_info *info = &nir_intrinsic_infos[intr->intrinsic];
+      if (!(info->flags & NIR_INTRINSIC_CAN_ELIMINATE))
+         return true;
+   }
+
+   bool live = false;
+   nir_foreach_ssa_def(instr, nir_instr_remove_and_dce_live_cb, &live);
+   return live;
+}
+
+/**
+ * Removes an instruction and any SSA defs that it used that are now dead, returning a nir_cursor
+ * where the instruction previously was.
+ */
+nir_cursor
+nir_instr_remove_and_dce(nir_instr *instr)
+{
+   nir_instr_worklist *worklist = nir_instr_worklist_create();
+
+   nir_instr_worklist_add_ssa_srcs(worklist, instr);
+   nir_cursor c = nir_instr_remove(instr);
+
+   nir_instr *dce_instr;
+   while ((dce_instr = nir_instr_worklist_pop_head(worklist))) {
+      /* Instrs can be in the worklist multiple times, so check
+       * that we haven't already removed this one.
+       */
+      if (exec_node_is_tail_sentinel(&dce_instr->node))
+         continue;
+
+      if (!nir_instr_remove_and_dce_is_live(dce_instr)) {
+         nir_instr_worklist_add_ssa_srcs(worklist, dce_instr);
+
+         /* If we're removing the instr where our cursor is, then we have to
+          * point the cursor elsewhere.
+          */
+         if ((c.option == nir_cursor_before_instr ||
+              c.option == nir_cursor_after_instr) &&
+             c.instr == dce_instr)
+            c = nir_instr_remove(dce_instr);
+         else
+            nir_instr_remove(dce_instr);
+      }
+   }
+
+   nir_instr_worklist_destroy(worklist);
+
+   return c;
+}
+
 /*@}*/
 
 void

src/compiler/nir/nir.h

@@ -3951,6 +3951,8 @@ nir_instr_remove(nir_instr *instr)
    return cursor;
 }
 
+nir_cursor nir_instr_remove_and_dce(nir_instr *instr);
+
 /** @} */
 
 nir_ssa_def *nir_instr_ssa_def(nir_instr *instr);

src/compiler/nir/nir_worklist.c

@@ -136,3 +136,20 @@ nir_block_worklist_pop_tail(nir_block_worklist *w)
    BITSET_CLEAR(w->blocks_present, w->blocks[tail]->index);
    return w->blocks[tail];
 }
+
+static bool
+nir_instr_worklist_add_srcs_cb(nir_src *src, void *state)
+{
+   nir_instr_worklist *wl = state;
+
+   if (src->is_ssa)
+      nir_instr_worklist_push_tail(wl, src->ssa->parent_instr);
+
+   return true;
+}
+
+void
+nir_instr_worklist_add_ssa_srcs(nir_instr_worklist *wl, nir_instr *instr)
+{
+   nir_foreach_src(instr, nir_instr_worklist_add_srcs_cb, wl);
+}

src/compiler/nir/nir_worklist.h

@@ -154,6 +154,9 @@ nir_instr_worklist_pop_head(nir_instr_worklist *wl)
    return *vec_instr;
 }
 
+void
+nir_instr_worklist_add_ssa_srcs(nir_instr_worklist *wl, nir_instr *instr);
+
 #define nir_foreach_instr_in_worklist(instr, wl) \
    for (nir_instr *instr; (instr = nir_instr_worklist_pop_head(wl));)
 

src/compiler/nir/tests/core_tests.cpp

@@ -0,0 +1,126 @@
+/*
+ * Copyright © 2018 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.
+ */
+
+#include <gtest/gtest.h>
+
+#include "nir.h"
+#include "nir_builder.h"
+
+namespace {
+
+class nir_core_test : public ::testing::Test {
+protected:
+   nir_core_test();
+   ~nir_core_test();
+
+   bool shader_contains_def(nir_ssa_def *def);
+
+   nir_builder *b, _b;
+};
+
+nir_core_test::nir_core_test()
+{
+   glsl_type_singleton_init_or_ref();
+
+   static const nir_shader_compiler_options options = { };
+   _b = nir_builder_init_simple_shader(MESA_SHADER_COMPUTE, &options, "builder test");
+   b = &_b;
+}
+
+nir_core_test::~nir_core_test()
+{
+   if (HasFailure()) {
+      printf("\nShader from the failed test:\n\n");
+      nir_print_shader(b->shader, stdout);
+   }
+
+   ralloc_free(b->shader);
+
+   glsl_type_singleton_decref();
+}
+
+struct contains_def_state {
+   nir_ssa_def *def;
+   bool found;
+};
+
+static bool
+contains_def_cb(nir_ssa_def *def, void *_state)
+{
+   struct contains_def_state *state = (struct contains_def_state *)_state;
+   if (def == state->def)
+      state->found = true;
+
+   return true;
+}
+
+bool
+nir_core_test::shader_contains_def(nir_ssa_def *def)
+{
+   nir_foreach_block(block, b->impl) {
+      nir_foreach_instr(instr, block) {
+         struct contains_def_state state = {
+            .def = def,
+            .found = false,
+         };
+         nir_foreach_ssa_def(instr, contains_def_cb, &state);
+         if (state.found)
+            return true;
+      }
+   }
+   return false;
+}
+
+TEST_F(nir_core_test, nir_instr_remove_and_dce_test)
+{
+   nir_ssa_def *zero = nir_imm_int(b, 0);
+   nir_ssa_def *one = nir_imm_int(b, 1);
+   nir_ssa_def *add01 = nir_iadd(b, zero, one);
+   nir_ssa_def *add11 = nir_iadd(b, one, one);
+
+   nir_cursor c = nir_instr_remove_and_dce(add01->parent_instr);
+   ASSERT_FALSE(shader_contains_def(add01));
+   ASSERT_TRUE(shader_contains_def(add11));
+   ASSERT_FALSE(shader_contains_def(zero));
+   ASSERT_TRUE(shader_contains_def(one));
+
+   ASSERT_TRUE(nir_cursors_equal(c, nir_before_instr(add11->parent_instr)));
+
+   nir_validate_shader(b->shader, "after remove_and_dce");
+}
+
+TEST_F(nir_core_test, nir_instr_remove_and_dce_all_test)
+{
+   nir_ssa_def *one = nir_imm_int(b, 1);
+   nir_ssa_def *add = nir_iadd(b, one, one);
+
+   nir_cursor c = nir_instr_remove_and_dce(add->parent_instr);
+   ASSERT_FALSE(shader_contains_def(add));
+   ASSERT_FALSE(shader_contains_def(one));
+
+   ASSERT_TRUE(nir_cursors_equal(c, nir_before_block(nir_start_block(b->impl))));
+
+   nir_validate_shader(b->shader, "after remove_and_dce");
+}
+
+}