Commit 07e62084 authored by Brian's avatar Brian

info about how the compiler works

parent 0e1bd230
......@@ -23,9 +23,10 @@ Contents
</p>
<ul>
<li><a href="#unsup">Unsupported Features</a>
<li><a href="#impl">Implementation Notes</a>
<li><a href="#notes">Implementation Notes</a>
<li><a href="#hints">Programming Hints</a>
<li><a href="#standalone">Stand-alone Compiler</a>
<li><a href="#implementation">Compiler Implementation</a>
</ul>
......@@ -50,7 +51,7 @@ All other major features of the shading language should function.
</p>
<a name="impl">
<a name="notes">
<h2>Implementation Notes</h2>
<ul>
......@@ -188,5 +189,53 @@ Over time, the correctness of the GPU programs, with respect to the ARB
and NV languagues, should improve.
</p>
<a name="implementation">
<h2>Compiler Implementation</h2>
<p>
The source code for Mesa's shading language compiler is in the
<code>src/mesa/shader/slang/</code> directory.
</p>
<p>
The compiler follows a fairly standard design and basically works as follows:
</p>
<ul>
<li>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.
<li>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.
<li>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.
<li>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.
<li>The emitted GPU instructions (see prog_instruction.h) are stored in a
gl_program object (see mtypes.h).
<li>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).
</ul>
<p>
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).
</p>
</BODY>
</HTML>
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment