Nikita Popov 2068b1ba03 [X86] Fix ABI for passing after i128 (#124134) ...

If we're passing an i128 value and we no longer have enough argument
registers (only r9 unallocated), the value gets passed via the stack.
However, r9 is still allocated as a shadow register, which means that a
following i64 argument will not use it. This doesn't match the x86-64
psABI.

Fix this by making i128 arguments as requiring consecutive registers,
and then adding a custom CC lowering that will allocate both parts of
the i128 at the same time, either to register or to stack, without
reserving a shadow register.

Fixes https://github.com/llvm/llvm-project/issues/123935.

2025-01-24 15:31:53 +01:00

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