Merge r298177 into the 4.0 branch : [X86] Add NumRegisterParameters Module Flag.

[tstellar]

Bugzilla Link	33174
Resolution	FIXED
Resolved on	May 31, 2017 07:01
Version	4.0
OS	All
Blocks	#31409
CC	@pcc

Extended Description

Is this patch OK to merge to the 4.0 branch?

[tstellar]

assigned to @tstellar

[zygoloid]

Looks like this is an LLVM IR ABI break: if we merge this, you won't be able to LTO code from clang 4.0.0 with code from clang 4.0.1 if you use -mregparm.

On the other hand, if we don't merge this, then building with -mregparm at all will potentially miscompile. I'm inclined to say that's more important than maintaining LLVM IR compatibility between patch releases here. Mechanically, the patch looks OK to merge, assuming you're OK with its implications.

I believe you also need to merge r298179 for this patch to have any effect.

[pcc]

Seems fine to me.

Regarding LTO'ing code from 4.0.0 with code from 4.0.1: that should still work. Linking a module with a module flag against another module without that module flag will give you a module with the module flag from the first module. That means that the backend will use the -mregparm flag from the 4.0.1 module, which is probably the best that we can do.

[tstellar]

Merged: r304238

[tstellar]

Accidentally updated the wrong bug, r304238 is the merge commit from a different bug.

[tstellar]

Merged: r304294