[LLVMdev] [RFC] Removing static initializers for command line options

[Owen Anderson]

> On Aug 19, 2014, at 10:24 PM, Chandler Carruth <chandlerc at google.com> wrote:
> 
> For example, we don't require all constants to be per-pass, and instead have per-file constants. Rafael is suggesting that one use case for cl::opt global variables is, in essence, a constant that is somewhat easier for a developer of LLVM (*not* a user) to change during debugging and active development. I don't think the desire for convenience and only supporting the default value in production contexts are completely invalid.

I think this statement ignores important debugging use cases, and over-simplifies the model of how LLVM-based frameworks are often developed.  As an example, say I develop an LLVM backend for a custom co-processor, and the compiler for it runs inside the software stack of the driver for my co-processor.  Per what you and Rafael are saying, the driver should not be able to programmatically set command line options to LLVM.  But this ignores the reality that, when developing my backend, I may still need to be able to twiddle debugging options when debugging a live driver stack.

Fundamentally, you argument is rooted in a world where LLVM debugging is always done on the llc or clang binaries, where the LLVM developer can easily modify the command line arguments themselves.  That’s not true of many use cases where LLVM as a shared library is relevant.

—Owen
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