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    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 */