Well, that was more work than I expected...

Tuesday, August 9, 2011
It's been a while since I posted. Usually when I "go dark" for an extended period of time, it's either because (a) I'm feeling burned out from working on Tart and need an extended break, or (b) it's because I'm working on a massive changeset and I don't want to talk about it too much until it's submitted. This time it's (b).

I've spent the last month or so updating Tart to work with the latest LLVM trunk. The LLVM APIs have changed significantly in preparation for the 3.0 release. The biggest change is that LLVM types now have first-class names, and types with different names are now distinct types even if they are structurally identical. In addition, the Opaque type is gone - instead you use a named struct with no body. (You can fill in the body later, or not.)

The APIs have also changed - Types are no longer "const" (that is, the LLVM APIs will no longer produce or accept values of type 'const Type *'). This required a huge number of edits to my code.

Also during this period I ran into several LLVM bugs in the new type system, and worked with the LLVM folks to diagnose and fix them. This includes a trip into DWARF hell, which is never fun.

In any case, I've committed the changes so Tart is working again. Overall, I like the changes - for one thing, the generated IR is easier to read now that types have proper names. And with the ability to declare a type name with no body, I'll eventually be able to reduce the amount of work the compiler is doing, because I won't have to do a deep analysis on fields that are never dereferenced.


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