[all-commits] [llvm/llvm-project] 16bd5c: Reland [AArch64] Copy x4/x5 vararg payload into th...

[Alex Bradbury via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 16bd5ce1184bb5683ea96290478e5912cf2975b9
      https://github.com/llvm/llvm-project/commit/16bd5ce1184bb5683ea96290478e5912cf2975b9
  Author: Alex Bradbury <asb at igalia.com>
  Date:   2026-07-13 (Mon, 13 Jul 2026)

  Changed paths:
    M llvm/lib/Target/AArch64/AArch64Arm64ECCallLowering.cpp
    M llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
    M llvm/test/CodeGen/AArch64/arm64ec-exit-thunks.ll
    M llvm/test/CodeGen/AArch64/arm64ec-hybrid-patchable.ll

  Log Message:
  -----------
  Reland [AArch64] Copy x4/x5 vararg payload into the x64 stack in Arm64EC exit thunks (#208453)

Reland llvm/llvm-project#190933, which was reverted by
llvm/llvm-project#198540 due to an EXPENSIVE_CHECKS build failure.

The fix relative to the reverted patch is to do the memcpy before the
final CALLSEQ_START for the dispatch call, avoiding nested call-frame
pseudos if memcpy lowers to a call.

Original commit message:
Currently the x4/x5 in a variadic Arm64EC exit thunks are treated by
LLVM like any other outgoing arguments. x4/x5 contain a pointer to the
first stack parameter and the size of the parameters passed on the
stack, and the generated exit thunk must memcpy these to the x86-64
stack. Current MSVC does this correctly.

Rather than introducing a new entry to the CallingConv enum, we mark the
call as vararg in AArch64ArmECCallLowering so that the lowering logic in
AArch64ISelLowering.cpp can recognise this case, perform the necessary
memcpy, and drop the x4/x5 arguments.

LLVM should additionally ensure that x0-x3 are mirrored to f0-f3 in
order to match the Windows x86-64 vararg ABI, but that change is left
for a follow-up patch.



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