A CIL Tutorial - Department of Computer Science - ETH Zürich

Chapter 10
Adding a New Kind of Statement
In this section, we will take a look at two dierent ways of adding a new statement to C without any
changes to the lexer or parser. In particular, we will add a statement to C that proles the cache
miss rate and used memory bandwidth in a block of code. Adding the new syntax and replacing
the new statement with calls into our runtime library will be the easy part. The more dicult task
will be the implementation of the runtime library. In particular, we must arrange for each thread
to maintain sucient state to handle arbitrary nesting of the new statement.
10.1 tut10.ml
The two dierent ways of adding syntax involve further use of the same attribute syntax that
we used for type qualiers. In the rst method, we transform a specially constructed if statement.
In the second method we transform Block statements that have been annotated with the
blockattribute ((...)) syntax supported by CIL. When using the transformed if statement,
we'll be able to use a C preprocessor macro to make it look more like a standard C statement.
First, we dene a string for the name of the new statement. Then, in hasCacheReportAttrs and
isCacheReportType, we dene functions for determining whether a type or set of attributes contains
the the name of the new statement.
let cacheReportStr = "cache report"
let hasCacheReportAttrs : attributes → bool = hasAttribute cacheReportStr
let isCacheReportType (t : typ) : bool = t | > typeAttrs | > hasCacheReportAttrs
The function isCacheReportState looks for two kinds of statements: either an if statement testing
the constant 0 cast to a type with the cache report attribute, or a Block with that attribute.
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