Done. I've added an extra parameter over what you might expect as classifyArgumentTypes doesn't seem to consider AAPCS16, whereas classifyReturnTypes does.
I've also renamed the variable to make the distinction between it and the function clearer.

I got bit a confused earlier. That does actually seem like correct behaviour (once we're no longer able to treat the struct as a homogeneous aggregate).
I've tightened up the conditional a bit as it wouldn't have previously accounted for the case where you had mfloat-abi=hard with an AAPCS (non VFP) attribute. Although in this instance, the backend does seem to be correcting/ignoring that, it's still best we don't blindly rely on such behaviour.

In D59094#1421893, @efriedma wrote:

Not sure how to write a testcase off the top of my head... have you tried homogeneous aggregates with more than two elements?

Not at all, thank you your comments.

Hi @eli.friedman, are you still happy to review this?

Removed the complicated frame pointer/ffixed combination errors in favour of an always on warning (in a new group, so it can be silenced).

Fixed an oversight where R6 could be used as the base pointer, even with ffixed-r6 specified.

Thanks for the changes! LGTM. Approved.

Added more test coverage, notably that to catch issues with using reserved registers for alignment and making up Thumb reg deficit.

More tests, and better handling of argument combination errors.

Thanks for posting this! Always good to doc updates.
Bit of _very_ opinionated bit of bike-shedding. Content otherwise LGTM!

Hi, we're currently working on similar functionality for the ARM backend, so I got pointed to take a look at this patch.
Looks good to me, I quite like the tablegen improvements, but agree with trong's comments.

Added cfe-commits.

Added llvm-commits.

Added some regression tests for invalid -ffixed-reg combinations and the declaration of (un)supported variables.

• Re-implementation using subtarget features over metadata.
• Reduction of register range to R5-R11.
• Additional checks to fix issues with spilling registers for stack alignment.

• Re-implementation using subtarget features over metadata.
• Reduction of register range to R5-R11.
• Additional checks to fix issues with spilling registers for stack alignment.
• Added clang errors for conflicting options with reserved registers.

Reworded -fstack-protector-all to bring it in line with the changes to the other two options.

Make thopre's suggested changes.

Edited Options.td directly, rather than the generated docs file.

Missing colon

Improved code formatting based on review