Leonard Chan c24d9d2b01 [llvm][IR] Add dso_local_equivalent Constant ... The `dso_local_equivalent` constant is a wrapper for functions that represents a value which is functionally equivalent to the global passed to this. That is, if this accepts a function, calling this constant should have the same effects as calling the function directly. This could be a direct reference to the function, the `@plt` modifier on X86/AArch64, a thunk, or anything that's equivalent to the resolved function as a call target. When lowered, the returned address must have a constant offset at link time from some other symbol defined within the same binary. The address of this value is also insignificant. The name is leveraged from `dso_local` where use of a function or variable is resolved to a symbol in the same linkage unit. In this patch: - Addition of `dso_local_equivalent` and handling it - Update Constant::needsRelocation() to strip constant inbound GEPs and take advantage of `dso_local_equivalent` for relative references This is useful for the [Relative VTables C++ ABI](https://reviews.llvm.org/D72959) which makes vtables readonly. This works by replacing the dynamic relocations for function pointers in them with static relocations that represent the offset between the vtable and virtual functions. If a function is externally defined, `dso_local_equivalent` can be used as a generic wrapper for the function to still allow for this static offset calculation to be done. See [RFC](http://lists.llvm.org/pipermail/llvm-dev/2020-August/144469.html) for more details. Differential Revision: https://reviews.llvm.org/D77248		2020-11-19 10:26:17 -08:00
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llvm	[llvm][IR] Add dso_local_equivalent Constant	2020-11-19 10:26:17 -08:00
llvm-c	C API: support scalable vectors	2020-10-28 18:19:34 -04:00