Only relevant for -Xfrontend -enable-copy-propagation in debug builds.
It's only an experimental mode for now for shrinking lifetimes while
providing lldb an easy way to report a friendly error.
Goals:
- two repetitive digits that don't look like garbage
- less than a page, so it can never be a real pointer
- reserve as many low bits as possible so it can't be a tagged pointer
- not used by any other memory smashers
0x440 is 64-byte aligned which is plenty for any conceivable object
allocator.
Poison sentinel value recognized by LLDB as a former reference to a
potentially deinitialized object. It uses no spare bits and cannot point to
readable memory.
This is not ABI per-se but does stay in-sync with LLDB. If it becomes
out-of-sync, then users won't see a friendly diagnostic when
inspecting references past their lifetime.
Define a generic 64-bit address space ABI which is capped at 56
bits. Switch ppc64 and s390x over to it.
This also allows String to have (roughly) the same representation
across 64-bit platforms.
Previously we had a single mask for all x86-64 targets which included both the top and bottom bits. This accommodated simulators, which use the top bit, while macOS uses the bottom bit, but reserved one bit more than necessary on each. This change breaks out x86-64 simulators from non-simulators and reserves only the one bit used on each.
rdar://problem/34805348 rdar://problem/29765919
* Reduce array abstraction on apple platforms dealing with literals
Part of the ongoing quest to reduce swift array literal abstraction
penalties: make the SIL optimizer able to eliminate bridging overhead
when dealing with array literals.
Introduce a new classify_bridge_object SIL instruction to handle the
logic of extracting platform specific bits from a Builtin.BridgeObject
value that indicate whether it contains a ObjC tagged pointer object,
or a normal ObjC object. This allows the SIL optimizer to eliminate
these, which allows constant folding a ton of code. On the example
added to test/SILOptimizer/static_arrays.swift, this results in 4x
less SIL code, and also leads to a lot more commonality between linux
and apple platform codegen when passing an array literal.
This also introduces a couple of SIL combines for patterns that occur
in the array literal passing case.
Move bits mask from Metadata.h to SwiftShims's HeapObject.h. This
exposes the bit masks to the stdlib, so that the stdlib doesn't have
to have its own magic numbers per-platform. This also enhances
readability for BridgeObject, whose magic numbers are mostly derived
from Swift's ABI.
