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
nir_cf_node_insert_after(nir_cf_node * node,nir_cf_node * after)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
nir_cf_node_insert_before(nir_cf_node * node,nir_cf_node * before)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
nir_cf_node_insert_begin(struct exec_list * list,nir_cf_node * node)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
nir_cf_node_insert_end(struct exec_list * list,nir_cf_node * node)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
nir_cf_list_clone_and_reinsert(nir_cf_list * src_list,nir_cf_node * parent,nir_cursor cursor,struct hash_table * remap_table)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
nir_cf_list_extract(nir_cf_list * extracted,struct exec_list * cf_list)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
nir_cf_node_remove(nir_cf_node * node)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 /** inserts undef phi sources from predcessor into phis of the block */
175 void nir_insert_phi_undef(nir_block *block, nir_block *pred);
176 
177 #ifdef __cplusplus
178 }
179 #endif
180 
181 #endif /* NIR_CONTROL_FLOW_H */
182