The Unladen Swallow project (faster Python, including an LLVM based JIT) found that LLVM wasn't really designed as a universal JIT compiler, or at least not one that was useful for languages such as Python. That was one of the reasons why they eventually stopped work on the project (although a lot of the non-LLVM work they did was still very good an useful and so the project as a whole was not wasted).
The Pypy developers (another Python with JIT project) looked very, very, carefully at every available JIT out there, and finally ended up writing their own. It was the only way that they could get something that would do what they needed. The results of doing that was performance that was far superior to what the Unladen Swallow project got when using LLVM.
It sounds very simple when you look at it from a distance. "We need a JIT, here's a JIT, let's use it." Then you find out that just because something is called a "JIT" doesn't mean that it will be of any use to what you are trying to do. The subject area is very complex and there will probably never be a universal solution.
What I could see the GCC JIT mode being useful for is things like generating certain critical portions of a program under programmer direction. That is, it would make a nice library that you call to generate very optimized code for specific functions or modules. A good example is how GCC is currently called in the background by a number of Python libraries which dynamically generate C code and compile it for faster execution. Being able to do this more directly via a JIT process could be very convenient. This is perhaps the sort of application that the author has in mind.
The Pypy developers (another Python with JIT project) looked very, very, carefully at every available JIT out there, and finally ended up writing their own. It was the only way that they could get something that would do what they needed. The results of doing that was performance that was far superior to what the Unladen Swallow project got when using LLVM.
It sounds very simple when you look at it from a distance. "We need a JIT, here's a JIT, let's use it." Then you find out that just because something is called a "JIT" doesn't mean that it will be of any use to what you are trying to do. The subject area is very complex and there will probably never be a universal solution.
What I could see the GCC JIT mode being useful for is things like generating certain critical portions of a program under programmer direction. That is, it would make a nice library that you call to generate very optimized code for specific functions or modules. A good example is how GCC is currently called in the background by a number of Python libraries which dynamically generate C code and compile it for faster execution. Being able to do this more directly via a JIT process could be very convenient. This is perhaps the sort of application that the author has in mind.