This patch adds support for lowering function calls with the
clang.arc.attachedcall bundle. The goal is to expand such calls to the
following sequence of instructions:
callq @fn movq %rax, %rdi callq _objc_retainAutoreleasedReturnValue / _objc_unsafeClaimAutoreleasedReturnValue
This sequence of instructions triggers Objective-C runtime optimizations,
hence we want to ensure no instructions get moved in between them.
This patch achieves that by adding a new CALL_RVMARKER ISD node,
which gets turned into the CALL64_RVMARKER pseudo, which eventually gets
expanded into the sequence mentioned above.
The ObjC runtime function to call is determined by the
argument in the bundle, which is passed through as a
target constant to the pseudo.
@ahatanak is working on using this attribute in the front- & middle-end.
Together with the front- & middle-end changes, this should address
PR31925 for X86.
This is the X86 version of 46bc40e50246c1902a1ca7916c8286cb837643ee,
which added similar support for AArch64.