[clang] [llvm] [X86][Windows] Return `fp128` on the stack (PR #204887)

[Trevor Gross via cfe-commits]

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@@ -299,6 +284,11 @@ Makes programs 10x faster by doing Special New Thing.
   two-register push in Windows x64 V3 unwind info. The directive takes two
   register operands: ``.seh_push2regs %r12, %r13``.
 
+* The `fp128` type is now passed via sret instead of XMM0 for some calling
+  conventions to match GCC. The C, Win64 and vectorcall calling conventions
+  now use sret, other calling conventions do not need to be compatible with
+  GCC and still return via XMM0.
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tgross35 wrote:

"passed via sret" should probably be "returned via sret"

https://github.com/llvm/llvm-project/pull/204887