imageworks/OpenShadingLanguage — pull request #270 by lgritz (2013-07-10 06:14:16+00:00)
Title: Important bug fixes for the recent peephole optimizations:

* If you change an instruction so that a symbol was written to in a spot
where it wasn't before, you MUST call block_unalias() to make sure to
end any notion of its being an alias for another symbol at that point
or later in the code block.
* Two code transformations that were legal only if a particular symbol
was not subsequently read neglected to consider that output parameters
or globals may be "read" after the shader is done executing and so not
having later read instructions within the shader is not a reliable
indicator.