src/glsl/nir/nir_control_flow.h

   1 /*
   2  * Copyright © 2014 Intel Corporation
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the next
  12  * paragraph) shall be included in all copies or substantial portions of the
  13  * Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  21  * IN THE SOFTWARE.
  22  *
  23  * Authors:
  24  *    Connor Abbott (cwabbott0@gmail.com)
  25  *
  26  */
  27
  28 #include "nir.h"
  29
  30 #pragma once
  31
  32 #ifdef __cplusplus
  33 extern "C" {
  34 #endif
  35
  36 /** NIR Control Flow Modification
  37  *
  38  * This file contains various API's that make modifying control flow in NIR,
  39  * while maintaining the invariants checked by the validator, much easier.
  40  * There are two parts to this:
  41  *
  42  * 1. Inserting control flow (if's and loops) in various places, for creating
  43  *    IR either from scratch or as part of some lowering pass.
  44  * 2. Taking existing pieces of the IR and either moving them around or
  45  *    deleting them.
  46  */
  47
  48 /* Helper struct for representing a point to extract/insert. Helps reduce the
  49  * combinatorial explosion of possible points to extract.
  50  */
  51
  52 typedef enum {
  53    nir_cursor_before_block,
  54    nir_cursor_after_block,
  55    nir_cursor_before_instr,
  56    nir_cursor_after_instr,
  57 } nir_cursor_option;
  58
  59 typedef struct {
  60    nir_cursor_option option;
  61    union {
  62       nir_block *block;
  63       nir_instr *instr;
  64    };
  65 } nir_cursor;
  66
  67 static inline nir_cursor
  68 nir_before_block(nir_block *block)
  69 {
  70    nir_cursor cursor;
  71    cursor.option = nir_cursor_before_block;
  72    cursor.block = block;
  73    return cursor;
  74 }
  75
  76 static inline nir_cursor
  77 nir_after_block(nir_block *block)
  78 {
  79    nir_cursor cursor;
  80    cursor.option = nir_cursor_after_block;
  81    cursor.block = block;
  82    return cursor;
  83 }
  84
  85 static inline nir_cursor
  86 nir_before_instr(nir_instr *instr)
  87 {
  88    nir_cursor cursor;
  89    cursor.option = nir_cursor_before_instr;
  90    cursor.instr = instr;
  91    return cursor;
  92 }
  93
  94 static inline nir_cursor
  95 nir_after_instr(nir_instr *instr)
  96 {
  97    nir_cursor cursor;
  98    cursor.option = nir_cursor_after_instr;
  99    cursor.instr = instr;
 100    return cursor;
 101 }
 102
 103 static inline nir_cursor
 104 nir_before_cf_node(nir_cf_node *node)
 105 {
 106    if (node->type == nir_cf_node_block)
 107       return nir_before_block(nir_cf_node_as_block(node));
 108
 109    return nir_after_block(nir_cf_node_as_block(nir_cf_node_prev(node)));
 110 }
 111
 112 static inline nir_cursor
 113 nir_after_cf_node(nir_cf_node *node)
 114 {
 115    if (node->type == nir_cf_node_block)
 116       return nir_after_block(nir_cf_node_as_block(node));
 117
 118    return nir_before_block(nir_cf_node_as_block(nir_cf_node_next(node)));
 119 }
 120
 121 static inline nir_cursor
 122 nir_before_cf_list(struct exec_list *cf_list)
 123 {
 124    nir_cf_node *first_node = exec_node_data(nir_cf_node,
 125                                             exec_list_get_head(cf_list), node);
 126    return nir_before_cf_node(first_node);
 127 }
 128
 129 static inline nir_cursor
 130 nir_after_cf_list(struct exec_list *cf_list)
 131 {
 132    nir_cf_node *last_node = exec_node_data(nir_cf_node,
 133                                            exec_list_get_tail(cf_list), node);
 134    return nir_after_cf_node(last_node);
 135 }
 136
 137 /** Control flow insertion. */
 138
 139 /** puts a control flow node where the cursor is */
 140 void nir_cf_node_insert(nir_cursor cursor, nir_cf_node *node);
 141
 142 /** puts a control flow node immediately after another control flow node */
 143 static inline void
 144 nir_cf_node_insert_after(nir_cf_node *node, nir_cf_node *after)
 145 {
 146    nir_cf_node_insert(nir_after_cf_node(node), after);
 147 }
 148
 149 /** puts a control flow node immediately before another control flow node */
 150 static inline void
 151 nir_cf_node_insert_before(nir_cf_node *node, nir_cf_node *before)
 152 {
 153    nir_cf_node_insert(nir_before_cf_node(node), before);
 154 }
 155
 156 /** puts a control flow node at the beginning of a list from an if, loop, or function */
 157 static inline void
 158 nir_cf_node_insert_begin(struct exec_list *list, nir_cf_node *node)
 159 {
 160    nir_cf_node_insert(nir_before_cf_list(list), node);
 161 }
 162
 163 /** puts a control flow node at the end of a list from an if, loop, or function */
 164 static inline void
 165 nir_cf_node_insert_end(struct exec_list *list, nir_cf_node *node)
 166 {
 167    nir_cf_node_insert(nir_after_cf_list(list), node);
 168 }
 169
 170
 171 /** Control flow motion.
 172  *
 173  * These functions let you take a part of a control flow list (basically
 174  * equivalent to a series of statement in GLSL) and "extract" it from the IR,
 175  * so that it's a free-floating piece of IR that can be either re-inserted
 176  * somewhere else or deleted entirely. A few notes on using it:
 177  *
 178  * 1. Phi nodes are considered attached to the piece of control flow that
 179  *    their sources come from. There are three places where phi nodes can
 180  *    occur, which are the three places where a block can have multiple
 181  *    predecessors:
 182  *
 183  *    1) After an if statement, if neither branch ends in a jump.
 184  *    2) After a loop, if there are multiple break's.
 185  *    3) At the beginning of a loop.
 186  *
 187  *    For #1, the phi node is considered to be part of the if, and for #2 and
 188  *    #3 the phi node is considered to be part of the loop. This allows us to
 189  *    keep phi's intact, but it means that phi nodes cannot be separated from
 190  *    the control flow they come from. For example, extracting an if without
 191  *    extracting all the phi nodes after it is not allowed, and neither is
 192  *    extracting only some of the phi nodes at the beginning of a block. It
 193  *    also means that extracting from the beginning of a basic block actually
 194  *    means extracting from the first non-phi instruction, since there's no
 195  *    situation where extracting phi nodes without extracting what comes
 196  *    before them makes any sense.
 197  *
 198  * 2. Phi node sources are guaranteed to remain valid, meaning that they still
 199  *    correspond one-to-one with the predecessors of the basic block they're
 200  *    part of. In addition, the original sources will be preserved unless they
 201  *    correspond to a break or continue that was deleted. However, no attempt
 202  *    is made to ensure that SSA form is maintained. In particular, it is
 203  *    *not* guaranteed that definitions of SSA values will dominate all their
 204  *    uses after all is said and done. Either the caller must ensure that this
 205  *    is the case, or it must insert extra phi nodes to restore SSA.
 206  *
 207  * 3. It is invalid to move a piece of IR with a break/continue outside of the
 208  *    loop it references. Doing this will result in invalid
 209  *    successors/predecessors and phi node sources.
 210  *
 211  * 4. It is invalid to move a piece of IR from one function implementation to
 212  *    another.
 213  *
 214  * 5. Extracting a control flow list will leave lots of dangling references to
 215  *    and from other pieces of the IR. It also leaves things in a not 100%
 216  *    consistent state. This means that some things (e.g. inserting
 217  *    instructions) might not work reliably on the extracted control flow. It
 218  *    also means that extracting control flow without re-inserting it or
 219  *    deleting it is a Bad Thing (tm).
 220  */
 221
 222 typedef struct {
 223    struct exec_list list;
 224    nir_function_impl *impl; /* for cleaning up if the list is deleted */
 225 } nir_cf_list;
 226
 227 void nir_cf_extract(nir_cf_list *extracted, nir_cursor begin, nir_cursor end);
 228
 229 void nir_cf_reinsert(nir_cf_list *cf_list, nir_cursor cursor);
 230
 231 void nir_cf_delete(nir_cf_list *cf_list);
 232
 233 static inline void
 234 nir_cf_list_extract(nir_cf_list *extracted, struct exec_list *cf_list)
 235 {
 236    nir_cf_extract(extracted, nir_before_cf_list(cf_list),
 237                   nir_after_cf_list(cf_list));
 238 }
 239
 240 /** removes a control flow node, doing any cleanup necessary */
 241 static inline void
 242 nir_cf_node_remove(nir_cf_node *node)
 243 {
 244    nir_cf_list list;
 245    nir_cf_extract(&list, nir_before_cf_node(node), nir_after_cf_node(node));
 246    nir_cf_delete(&list);
 247 }
 248
 249 #ifdef __cplusplus
 250 }
 251 #endif