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Diffstat (limited to 'src/glsl/README')
| -rw-r--r-- | src/glsl/README | 46 |
1 files changed, 42 insertions, 4 deletions
diff --git a/src/glsl/README b/src/glsl/README index 2e501d6206..dd80a53d47 100644 --- a/src/glsl/README +++ b/src/glsl/README @@ -156,10 +156,10 @@ for the 965 fragment shader backend when that is developed. Q: How should I expand instructions that take multiple backend instructions? Sometimes you'll have to do the expansion in your code generation -- -see, for example, ir_to_mesa.cpp's handling of ir_binop_mul for -matrices. However, in many cases you'll want to do a pass over the IR -to convert non-native instructions to a series of native instructions. -For example, for the Mesa backend we have ir_div_to_mul_rcp.cpp because +see, for example, ir_to_mesa.cpp's handling of ir_unop_sqrt. However, +in many cases you'll want to do a pass over the IR to convert +non-native instructions to a series of native instructions. For +example, for the Mesa backend we have ir_div_to_mul_rcp.cpp because Mesa IR (and many hardware backends) only have a reciprocal instruction, not a divide. Implementing non-native instructions this way gives the chance for constant folding to occur, so (a / 2.0) @@ -189,3 +189,41 @@ You may also need to update the backends if they will see the new expr type: You can then use the new expression from builtins (if all backends would rather see it), or scan the IR and convert to use your new expression type (see ir_mod_to_fract, for example). + +Q: How is memory management handled in the compiler? + +The hierarchical memory allocator "talloc" developed for the Samba +project is used, so that things like optimization passes don't have to +worry about their garbage collection so much. It has a few nice +features, including low performance overhead and good debugging +support that's trivially available. + +Generally, each stage of the compile creates a talloc context and +allocates its memory out of that or children of it. At the end of the +stage, the pieces still live are stolen to a new context and the old +one freed, or the whole context is kept for use by the next stage. + +For IR transformations, a temporary context is used, then at the end +of all transformations, reparent_ir reparents all live nodes under the +shader's IR list, and the old context full of dead nodes is freed. +When developing a single IR transformation pass, this means that you +want to allocate instruction nodes out of the temporary context, so if +it becomes dead it doesn't live on as the child of a live node. At +the moment, optimization passes aren't passed that temporary context, +so they find it by calling talloc_parent() on a nearby IR node. The +talloc_parent() call is expensive, so many passes will cache the +result of the first talloc_parent(). Cleaning up all the optimization +passes to take a context argument and not call talloc_parent() is left +as an exercise. + +Q: What is the file naming convention in this directory? + +Initially, there really wasn't one. We have since adopted one: + + - Files that implement code lowering passes should be named lower_* + (e.g., lower_noise.cpp). + - Files that implement optimization passes should be named opt_*. + - Files that implement a class that is used throught the code should + take the name of that class (e.g., ir_hierarchical_visitor.cpp). + - Files that contain code not fitting in one of the previous + categories should have a sensible name (e.g., glsl_parser.ypp). |