[clang] [clang] Always pass fp128 arguments indirectly on Windows (PR #115052)

[Trevor Gross via cfe-commits]

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@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -triple x86_64-windows-gnu -emit-llvm -o - %s \
+// RUN:    | FileCheck %s --check-prefix=GNU64
+// __float128 is unsupported on MSVC
+
+__float128 fp128_ret(void) { return 0; }
+// GNU64: define dso_local void @fp128_ret(ptr dead_on_unwind noalias writable sret(fp128) align 16 %agg.result)
+
+__float128 fp128_args(__float128 a, __float128 b) { return a * b; }
+// GNU64: define dso_local void @fp128_args(ptr dead_on_unwind noalias writable sret(fp128) align 16 %agg.result, ptr noundef %0, ptr noundef %1)
+
+void fp128_vararg(int a, ...) {
+  // GNU64-LABEL: define dso_local void @fp128_vararg
+  __builtin_va_list ap;
+  __builtin_va_start(ap, a);
+  __float128 i = __builtin_va_arg(ap, __float128);
+  // GNU64: load ptr, ptr
+  // GNU64: load fp128, ptr
+  __builtin_va_end(ap);
+}
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tgross35 wrote:

This isn't sufficient to identify the varargs crash, I don't think that is possible without an asm or execution test. Should I add one somewhere?

https://github.com/llvm/llvm-project/pull/115052