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.)
Within each function that launches tasks, we now can easily track which
tasks that function launched, so that the sync at the end of the function
can just sync on the tasks launched by that function (not all tasks
launched by all functions.)
Implementing this led to a rework of the task system API that ispc generates
code to call; the example task systems in examples/tasksys.cpp have been
updated to conform to this API. (The updated API is also documented in
the ispc user's guide.)
As part of this, "launch[n]" syntax was added to launch a number of tasks
in a single launch statement, rather than requiring a loop over 'n' to
launch n tasks.
This commit thus fixes issue #84 (enhancement to launch multiple tasks from
a single launch statement) as well as issue #105 (recursive task launches
were broken).
The intent is that the code in stdlib.ispc that is calling out to the built-ins
should match argument types exactly (using explicit casts as needed), just
for maximal clarity/safety.
Go back to running both sides of 'if' statements with masking and without
branching if we can determine that the code is relatively simple (as per
the simple cost model), and is safe to run even if the mask is 'all off'.
This gives a bit of a performance improvement for some of the examples
(most notably, the ray tracer), and is the code that one wants generated
in this case anyhow.
This is currently only used to decide whether it's worth doing an
"are all lanes running" check at the start of functions--for small
functions, it's not worth the overhead.
The cost is estimated relatively early in compilation (e.g. before
we know if an array access is a scatter/gather or not, before
constant folding, etc.), so there are many known shortcomings.
Fixes issue #73. Previously, if we had e.g. an int16 type that was being shifted
left by 1, then the constant integer 1 would come in as an int32, we'd convert
the int16 to an int32, and then we'd do the shift. Now, for shifts, the type
of the expression is always the same as the type of the value being shifted.
This commit adds support for swizzles like "foo.zy" (if "foo" is,
for example, a float<3> type) as rvalues. (Still need support for
swizzles as lvalues.)
