src/compiler/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 #ifndef NIR_CONTROL_FLOW_H
  29 #define NIR_CONTROL_FLOW_H
  30
  31 #include "nir.h"
  32
  33 #ifdef __cplusplus
  34 extern "C" {
  35 #endif
  36
  37 /** NIR Control Flow Modification
  38  *
  39  * This file contains various APIs that make modifying control flow in NIR,
  40  * while maintaining the invariants checked by the validator, much easier.
  41  * There are two parts to this:
  42  *
  43  * 1. Inserting control flow (ifs and loops) in various places, for creating
  44  *    IR either from scratch or as part of some lowering pass.
  45  * 2. Taking existing pieces of the IR and either moving them around or
  46  *    deleting them.
  47  */
  48
  49 /** Control flow insertion. */
  50
  51 /** puts a control flow node where the cursor is */
  52 void nir_cf_node_insert(nir_cursor cursor, nir_cf_node *node);
  53
  54 /** puts a control flow node immediately after another control flow node */
  55 static inline void
  56 nir_cf_node_insert_after(nir_cf_node *node, nir_cf_node *after)
  57 {
  58    nir_cf_node_insert(nir_after_cf_node(node), after);
  59 }
  60
  61 /** puts a control flow node immediately before another control flow node */
  62 static inline void
  63 nir_cf_node_insert_before(nir_cf_node *node, nir_cf_node *before)
  64 {
  65    nir_cf_node_insert(nir_before_cf_node(node), before);
  66 }
  67
  68 /** puts a control flow node at the beginning of a list from an if, loop, or function */
  69 static inline void
  70 nir_cf_node_insert_begin(struct exec_list *list, nir_cf_node *node)
  71 {
  72    nir_cf_node_insert(nir_before_cf_list(list), node);
  73 }
  74
  75 /** puts a control flow node at the end of a list from an if, loop, or function */
  76 static inline void
  77 nir_cf_node_insert_end(struct exec_list *list, nir_cf_node *node)
  78 {
  79    nir_cf_node_insert(nir_after_cf_list(list), node);
  80 }
  81
  82
  83 /** Control flow motion.
  84  *
  85  * These functions let you take a part of a control flow list (basically
  86  * equivalent to a series of statement in GLSL) and "extract" it from the IR,
  87  * so that it's a free-floating piece of IR that can be either re-inserted
  88  * somewhere else or deleted entirely. A few notes on using it:
  89  *
  90  * 1. Phi nodes are considered attached to the piece of control flow that
  91  *    their sources come from. There are three places where phi nodes can
  92  *    occur, which are the three places where a block can have multiple
  93  *    predecessors:
  94  *
  95  *    1) After an if statement, if neither branch ends in a jump.
  96  *    2) After a loop, if there are multiple breaks.
  97  *    3) At the beginning of a loop.
  98  *
  99  *    For #1, the phi node is considered to be part of the if, and for #2 and
 100  *    #3 the phi node is considered to be part of the loop. This allows us to
 101  *    keep phis intact, but it means that phi nodes cannot be separated from
 102  *    the control flow they come from. For example, extracting an if without
 103  *    extracting all the phi nodes after it is not allowed, and neither is
 104  *    extracting only some of the phi nodes at the beginning of a block. It
 105  *    also means that extracting from the beginning of a basic block actually
 106  *    means extracting from the first non-phi instruction, since there's no
 107  *    situation where extracting phi nodes without extracting what comes
 108  *    before them makes any sense.
 109  *
 110  * 2. Phi node sources are guaranteed to remain valid, meaning that they still
 111  *    correspond one-to-one with the predecessors of the basic block they're
 112  *    part of. In addition, the original sources will be preserved unless they
 113  *    correspond to a break or continue that was deleted. However, no attempt
 114  *    is made to ensure that SSA form is maintained. In particular, it is
 115  *    *not* guaranteed that definitions of SSA values will dominate all their
 116  *    uses after all is said and done. Either the caller must ensure that this
 117  *    is the case, or it must insert extra phi nodes to restore SSA.
 118  *
 119  * 3. It is invalid to move a piece of IR with a break/continue outside of the
 120  *    loop it references. Doing this will result in invalid
 121  *    successors/predecessors and phi node sources.
 122  *
 123  * 4. It is invalid to move a piece of IR from one function implementation to
 124  *    another.
 125  *
 126  * 5. Extracting a control flow list will leave lots of dangling references to
 127  *    and from other pieces of the IR. It also leaves things in a not 100%
 128  *    consistent state. This means that some things (e.g. inserting
 129  *    instructions) might not work reliably on the extracted control flow. It
 130  *    also means that extracting control flow without re-inserting it or
 131  *    deleting it is a Bad Thing (tm).
 132  */
 133
 134 typedef struct {
 135    struct exec_list list;
 136    nir_function_impl *impl; /* for cleaning up if the list is deleted */
 137 } nir_cf_list;
 138
 139 void nir_cf_extract(nir_cf_list *extracted, nir_cursor begin, nir_cursor end);
 140
 141 void nir_cf_reinsert(nir_cf_list *cf_list, nir_cursor cursor);
 142
 143 void nir_cf_delete(nir_cf_list *cf_list);
 144
 145 void nir_cf_list_clone(nir_cf_list *dst, nir_cf_list *src, nir_cf_node *parent,
 146                        struct hash_table *remap_table);
 147
 148 static inline void
 149 nir_cf_list_clone_and_reinsert(nir_cf_list *src_list, nir_cf_node *parent,
 150                                nir_cursor cursor,
 151                                struct hash_table *remap_table)
 152 {
 153    nir_cf_list list;
 154    nir_cf_list_clone(&list, src_list, parent, remap_table);
 155    nir_cf_reinsert(&list, cursor);
 156 }
 157
 158 static inline void
 159 nir_cf_list_extract(nir_cf_list *extracted, struct exec_list *cf_list)
 160 {
 161    nir_cf_extract(extracted, nir_before_cf_list(cf_list),
 162                   nir_after_cf_list(cf_list));
 163 }
 164
 165 /** removes a control flow node, doing any cleanup necessary */
 166 static inline void
 167 nir_cf_node_remove(nir_cf_node *node)
 168 {
 169    nir_cf_list list;
 170    nir_cf_extract(&list, nir_before_cf_node(node), nir_after_cf_node(node));
 171    nir_cf_delete(&list);
 172 }
 173
 174 #ifdef __cplusplus
 175 }
 176 #endif
 177
 178 #endif /* NIR_CONTROL_FLOW_H */