[LLVMdev] New Configure Option for LLVM Builds

[Justin Holewinski]

For the PTX back-end, I would like to introduce a configure-time option to determine the number of architectural registers available to LLVM register allocation during code generation.  The motivation for this is PTX is a virtual instruction set and the number of registers is configurable in the output file.  Thus, the number of registers specified via tablegen is arbitrary.  For different use-cases, it may be desirable to change this number.

That said, my question is in regards to how best to implement this considering that the PTX back-end is a part of upstream LLVM and the new option will be committed to LLVM trunk.  Creating a new option seems trivial for the CMake build scripts; just add a special target to automatically generate parts of the PTXRegisterInfo.td file.  The Autotools build scripts seem to complicate matters, however.  The makefiles for the different back-ends appear to be regular makefiles that are not processed by automake, making it difficult to introduce configure-time variables.

Is the introduction of a configure-time variable in the CMake build scripts an acceptable addition in LLVM trunk?
Is there any precedent for backend-specific configure options?  Would the autotools-based build system need to be modified to get something like this to work?

Thanks,

Justin Holewinski

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