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