[LLVMdev] adding support for -ffixed-<reg>
mcurtis at codeaurora.org
Wed Oct 3 08:46:02 PDT 2012
On 10/3/2012 12:29 AM, Chris Lattner wrote:
> On Oct 2, 2012, at 7:23 AM, Matthew Curtis <mcurtis at codeaurora.org
> <mailto:mcurtis at codeaurora.org>> wrote:
>> I'm adding support for -ffixed-<reg>
>> for Hexagon and was wondering if I should do it in such a way that
>> other targets get the support as well by default or if a given target
>> back-end should have to explicitly opt-in for support.
> It would be great to have this as a target-indepentent (well,
> obviously the specific register names are target specific, you know
> what I mean) compiler feature. This is one of the blocking issues
> preventing some portion of the Linux kernel from "just working" with LLVM.
> From the design perspective, I think it would make sense to represent
> this in LLVM IR with named metadata
> (http://llvm.org/docs/LangRef.html#namedmetadatastructure) like
> "!llvm.fixedregs". This could then be picked up by the code
> generator, installed as preallocated registers (Jakob would be the one
> to ask how best to do this).
> If you're not in a huge hurry, an even better way to model this is
> with Bill Wendling's work on generalized function attributes. Our
> eventual goal is to allow arbitrary target-specific function
> attributes. Modeling this list as a per-function attribute would be
> much cleaner, and allow -ffixed-<reg> to work with LTO.
We currently have a working solution that satisfies the needs of our
internal users, so we're not in a huge hurry.
Depending on the timeline for generalized function attributes, I'd like
to pursue this as the preferred solution. I will follow-up with Bill.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation
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