[all-commits] [llvm/llvm-project] dd70ae: [x86_64][windows][swift] do not use Swift async ex...

[Alex Lorenz via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: dd70aef05a86bb0c1e04c49cc1bd0457ca362ce3
      https://github.com/llvm/llvm-project/commit/dd70aef05a86bb0c1e04c49cc1bd0457ca362ce3
  Author: Alex Lorenz <arphaman at gmail.com>
  Date:   2024-02-05 (Mon, 05 Feb 2024)

  Changed paths:
    M llvm/lib/Target/X86/X86FrameLowering.cpp
    M llvm/lib/Target/X86/X86ISelLowering.cpp
    M llvm/lib/Target/X86/X86ISelLowering.h
    M llvm/lib/Target/X86/X86ISelLoweringCall.cpp
    M llvm/test/CodeGen/X86/swift-async-win64.ll

  Log Message:
  -----------
  [x86_64][windows][swift] do not use Swift async extended frame for wi… (#80468)

…ndows x86_64
targets that use windows 64 prologue

Windows x86_64 stack frame layout is currently not compatible with
Swift's async extended frame, which reserves the slot right below RBP
(RBP-8) for the async context pointer, as it doesn't account for the
fact that a stack object in a win64 frame can be allocated at the same
location. This can cause issues at runtime, for instance, Swift's TCA
test code has functions that fail because of this issue, as they spill a
value to that slack slot, which then gets overwritten by a store into
address returned by the @llvm.swift.async.context.addr() intrinsic (that
ends up being RBP - 8), leading to an incorrect value being used at a
later point when that stack slot is being read from again. This change
drops the use of async extended frame for windows x86_64 subtargets and
instead uses the x32 based approach of allocating a separate stack slot
for the stored async context pointer.

Additionally, LLDB which is the primary consumer of the extended frame
makes assumptions like checking for a saved previous frame pointer at
the current frame pointer address, which is also incompatible with the
windows x86_64 frame layout, as the previous frame pointer is not
guaranteed to be stored at the current frame pointer address. Therefore
the extended frame layout can be turned off to fix the current
miscompile without introducing regression into LLDB for windows x86_64
as it already doesn't work correctly. I am still investigating what
should be made for LLDB to support using an allocated stack slot to
store the async frame context instead of being located at RBP - 8 for
windows.