diff options
Diffstat (limited to 'src/glsl/nir/nir_control_flow.h')
| -rw-r--r-- | src/glsl/nir/nir_control_flow.h | 75 |
1 files changed, 75 insertions, 0 deletions
diff --git a/src/glsl/nir/nir_control_flow.h b/src/glsl/nir/nir_control_flow.h index 5a3be260f63..45aff3e61be 100644 --- a/src/glsl/nir/nir_control_flow.h +++ b/src/glsl/nir/nir_control_flow.h @@ -37,6 +37,12 @@ extern "C" { * * This file contains various API's that make modifying control flow in NIR, * while maintaining the invariants checked by the validator, much easier. + * There are two parts to this: + * + * 1. Inserting control flow (if's and loops) in various places, for creating + * IR either from scratch or as part of some lowering pass. + * 2. Taking existing pieces of the IR and either moving them around or + * deleting them. */ /* Helper struct for representing a point to extract/insert. Helps reduce the @@ -164,6 +170,75 @@ nir_cf_node_insert_end(struct exec_list *list, nir_cf_node *node) /** removes a control flow node, doing any cleanup necessary */ void nir_cf_node_remove(nir_cf_node *node); +/** Control flow motion. + * + * These functions let you take a part of a control flow list (basically + * equivalent to a series of statement in GLSL) and "extract" it from the IR, + * so that it's a free-floating piece of IR that can be either re-inserted + * somewhere else or deleted entirely. A few notes on using it: + * + * 1. Phi nodes are considered attached to the piece of control flow that + * their sources come from. There are three places where phi nodes can + * occur, which are the three places where a block can have multiple + * predecessors: + * + * 1) After an if statement, if neither branch ends in a jump. + * 2) After a loop, if there are multiple break's. + * 3) At the beginning of a loop. + * + * For #1, the phi node is considered to be part of the if, and for #2 and + * #3 the phi node is considered to be part of the loop. This allows us to + * keep phi's intact, but it means that phi nodes cannot be separated from + * the control flow they come from. For example, extracting an if without + * extracting all the phi nodes after it is not allowed, and neither is + * extracting only some of the phi nodes at the beginning of a block. It + * also means that extracting from the beginning of a basic block actually + * means extracting from the first non-phi instruction, since there's no + * situation where extracting phi nodes without extracting what comes + * before them makes any sense. + * + * 2. Phi node sources are guaranteed to remain valid, meaning that they still + * correspond one-to-one with the predecessors of the basic block they're + * part of. In addition, the original sources will be preserved unless they + * correspond to a break or continue that was deleted. However, no attempt + * is made to ensure that SSA form is maintained. In particular, it is + * *not* guaranteed that definitions of SSA values will dominate all their + * uses after all is said and done. Either the caller must ensure that this + * is the case, or it must insert extra phi nodes to restore SSA. + * + * 3. It is invalid to move a piece of IR with a break/continue outside of the + * loop it references. Doing this will result in invalid + * successors/predecessors and phi node sources. + * + * 4. It is invalid to move a piece of IR from one function implementation to + * another. + * + * 5. Extracting a control flow list will leave lots of dangling references to + * and from other pieces of the IR. It also leaves things in a not 100% + * consistent state. This means that some things (e.g. inserting + * instructions) might not work reliably on the extracted control flow. It + * also means that extracting control flow without re-inserting it or + * deleting it is a Bad Thing (tm). + */ + +typedef struct { + struct exec_list list; + nir_function_impl *impl; /* for cleaning up if the list is deleted */ +} nir_cf_list; + +void nir_cf_extract(nir_cf_list *extracted, nir_cursor begin, nir_cursor end); + +void nir_cf_reinsert(nir_cf_list *cf_list, nir_cursor cursor); + +void nir_cf_delete(nir_cf_list *cf_list); + +static inline void +nir_cf_list_extract(nir_cf_list *extracted, struct exec_list *cf_list) +{ + nir_cf_extract(extracted, nir_before_cf_list(cf_list), + nir_after_cf_list(cf_list)); +} + #ifdef __cplusplus } #endif |