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| -rw-r--r-- | src/glsl/lower_jumps.cpp | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/src/glsl/lower_jumps.cpp b/src/glsl/lower_jumps.cpp index beacfaf8b03..9cd15ef7366 100644 --- a/src/glsl/lower_jumps.cpp +++ b/src/glsl/lower_jumps.cpp @@ -23,6 +23,37 @@ /** * \file lower_jumps.cpp + * + * This pass lowers jumps (break, continue, and return) to if/else structures. + * + * It can be asked to: + * 1. Pull jumps out of ifs where possible + * 2. Remove all "continue"s, replacing them with an "execute flag" + * 3. Replace all "break" with a single conditional one at the end of the loop + * 4. Replace all "return"s with a single return at the end of the function, + * for the main function and/or other functions + * + * Applying this pass gives several benefits: + * 1. All functions can be inlined. + * 2. nv40 and other pre-DX10 chips without "continue" can be supported + * 3. nv30 and other pre-DX10 chips with no control flow at all are better + * supported + * + * Continues are lowered by adding a per-loop "execute flag", initialized to + * true, that when cleared inhibits all execution until the end of the loop. + * + * Breaks are lowered to continues, plus setting a "break flag" that is checked + * at the end of the loop, and trigger the unique "break". + * + * Returns are lowered to breaks/continues, plus adding a "return flag" that + * causes loops to break again out of their enclosing loops until all the + * loops are exited: then the "execute flag" logic will ignore everything + * until the end of the function. + * + * Note that "continue" and "return" can also be implemented by adding + * a dummy loop and using break. + * However, this is bad for hardware with limited nesting depth, and + * prevents further optimization, and thus is not currently performed. */ #include "glsl_types.h" |