On 20/10/18 16:07, Simon Kissel wrote:
- Complete the LLVM branch of FPC. It looks like Jonas has stopped working on it two years ago, which is a pity.
I didn't stop working on it, but I didn't make real progress anymore either. The current state of the LLVM code generator is that everything works on Darwin/x86-64, except for a) exception handling in general: indeed needs DWARF-EH support in the RTL, and also support for the LLVM exception handling intrinsics in the code generator. I've worked on and off on this and have some local patches, but it's not complete b) hardware exceptions (null pointer, floating point): the LLVM versions I worked with back then did not support support any form of hardware exceptions. If a memory access faults, the result is undefined behaviour (even with full exception support in the LLVM IR). If a floating point instruction throw an exception, the result is undefined (although they have been working a bit on it since then). This is not something that can be changed/fixed in FPC, and is quite different from how FPC's current code generator works (I don't know how Embarcardero deals with it in their LLVM-based code generator).
Additionally, in the current FPC code generator global variables behave mostly as volatile variables. With LLVM, that won't be the case (unless we mark all of their accesses as volatile, but that would obviously inhibit LLVM optimizations). This may break some multithreaded code that currently works, and would probably require the introduction of a volatile() operatator (similar to the unaligned() one). On the other hand, I already added support for tracking the volatile state of references in the past, so that should be easy to do.
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