Specifically, stmts and exprs are no longer responsible for first recursively
optimizing their children before doing their own optimization (this turned
out to be error-prone, with children sometimes being forgotten.) They now
are just responsible for their own optimization, when appropriate.
In general, it should just return the original node pointer, but for type checking
and optimization passes, it can return a new value for the node (that will be
assigned where the old one was in the tree.)
Along the way, fixed some bugs in WalkAST() where the postorder callback wouldn't
end up being called for a few expr types (sizeof, dereference, address of,
reference).
For starters, use it for the check to see if code is safe to run with the
mask all off.
This also fixes a bug where we would sometimes incorrectly say that
a whole block of code was unsafe to run with an all off mask because we came
to a NULL AST node during traversal.
Be better about tracking the full extent of expressions in the parser;
this leads to more intelligible error messages when we indicate where
exactly the error happened.
The stuff in decl.h/decl.cpp is messy, largely due to its close mapping
to C-style variable declarations. This checkin has updated code throughout
all of the declaration statement, variable, and function code that operates
on symbols and types directly. Thus, Decl* related stuff is now localized
to decl.h/decl.cpp and the parser.
Issue #13.
Added AST and Function classes.
Now, we parse the whole file and build up the AST for all of the
functions in the Module before we emit IR for the functions (vs. before,
when we generated IR along the way as we parsed the source file.)
