[llvm-dev] Per-function subtargets

[Eric Christopher via llvm-dev]

The intent is that there should be no module level attribute that
affects anything beyond ABI level decisions. The module level
attributes should control things where you cannot link two modules
together and still have an ABI conforming program. Everything else
should be on the function and such the subtarget.

Make sense?

-eric

On Wed, Mar 13, 2019 at 1:51 PM via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>
> I've been trying to understand the current state of subtargets and
> subtarget features in LLVM. It seems like the presence of "target-cpu"
> and "target-features" attributes on IR functions are currently intended
> to take precedence over the module-level (TargetMachine) versions. See
> X86TargetMachine::getSubtargetImpl for an example of this. However, this
> feels like it is half-way between two solutions (either all-module-wide,
> or all-function-specific), and some previous discussions like
> https://groups.google.com/forum/#!topic/llvm-dev/2hp9aARHEJA ([LLVMdev]
> Embedding cpu and feature strings into IR and enabling switching
> subtarget on a per function basis) seem to reinforce that feeling.
>
> Is the intent still to eventually remove the module-level subtarget
> options entirely? Or will the two continue to coexist? Is it up to the
> target to decide how to "merge" the two, or is the "all or nothing"
> approach the right one?
>
> --
> Scott
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