+Compiler Implementation
+
+
+The source code for Mesa's shading language compiler is in the
+src/mesa/shader/slang/ directory.
+
+
+
+The compiler follows a fairly standard design and basically works as follows:
+
+
+- The input string is tokenized (see grammar.c) and parsed
+(see slang_compiler_*.c) to produce an Abstract Syntax Tree (AST).
+The nodes in this tree are slang_operation structures
+(see slang_compile_operation.h).
+The nodes are decorated with symbol table, scoping and datatype information.
+
- The AST is converted into an Intermediate representation (IR) tree
+(see the slang_codegen.c file).
+The IR nodes represent basic GPU instructions, like add, dot product,
+move, etc.
+The IR tree is mostly a binary tree, but a few nodes have three or four
+children.
+In principle, the IR tree could be executed by doing an in-order traversal.
+
- The IR tree is traversed in-order to emit code (see slang_emit.c).
+This is also when registers are allocated to store variables and temps.
+
- In the future, a pattern-matching code generator-generator may be
+used for code generation.
+Programs such as L-BURG (Bottom-Up Rewrite Generator) and Twig look for
+patterns in IR trees, compute weights for subtrees and use the weights
+to select the best instructions to represent the sub-tree.
+
- The emitted GPU instructions (see prog_instruction.h) are stored in a
+gl_program object (see mtypes.h).
+
- When a fragment shader and vertex shader are linked (see slang_link.c)
+the varying vars are matched up, uniforms are merged, and vertex
+attributes are resolved (rewriting instructions as needed).
+
+
+
+The final vertex and fragment programs may be interpreted in software
+(see prog_execute.c) or translated into a specific hardware architecture
+(see drivers/dri/i915/i915_fragprog.c for example).
+
+
+
+