From a44e9328069f4a73e528f2c4e39e45324fe08788 Mon Sep 17 00:00:00 2001
From: Christoffer Lerno <christoffer@aegik.com>
Date: Wed, 16 Apr 2025 15:58:14 +0200
Subject: [PATCH] ABI bug on x64 Linux / MacOS when passing a union containing
 a struct of 3 floats. #2087

---
 releasenotes.md                               |  1 +
 src/compiler/abi/c_abi_x64.c                  |  2 +-
 test/test_suite/abi/sysv_union_struct_vec.c3t | 47 +++++++++++++++++++
 3 files changed, 49 insertions(+), 1 deletion(-)
 create mode 100644 test/test_suite/abi/sysv_union_struct_vec.c3t

diff --git a/releasenotes.md b/releasenotes.md
index 5bd22fe11..51579469b 100644
--- a/releasenotes.md
+++ b/releasenotes.md
@@ -19,6 +19,7 @@
 - Incorrect rounding at compile time going from double to int.
 - Regression with invalid setup of the WASM temp allocator.
 - Correctly detect multiple overloads of the same type.
+- ABI bug on x64 Linux / MacOS when passing a union containing a struct of 3 floats. #2087 
 
 ### Stdlib changes
 - Hash functions for integer vectors and arrays.
diff --git a/src/compiler/abi/c_abi_x64.c b/src/compiler/abi/c_abi_x64.c
index be1b369c7..744c3d799 100644
--- a/src/compiler/abi/c_abi_x64.c
+++ b/src/compiler/abi/c_abi_x64.c
@@ -491,7 +491,7 @@ bool x64_contains_float_at_offset(Type *type, unsigned offset)
 static Type *x64_get_fp_type_at_offset(Type *type, unsigned ir_offset)
 {
 	if (!ir_offset && type_is_float(type)) return type;
-	if (type->type_kind == TYPE_STRUCT)
+	if (type->type_kind == TYPE_STRUCT || type->type_kind == TYPE_UNION)
 	{
 		Decl *element = x64_get_member_at_offset(type->decl, ir_offset);
 		return x64_get_fp_type_at_offset(element->type, ir_offset - element->offset);
diff --git a/test/test_suite/abi/sysv_union_struct_vec.c3t b/test/test_suite/abi/sysv_union_struct_vec.c3t
new file mode 100644
index 000000000..477c6a55d
--- /dev/null
+++ b/test/test_suite/abi/sysv_union_struct_vec.c3t
@@ -0,0 +1,47 @@
+// #target: macos-x64
+// Struct-in-union bug #2087
+module test;
+
+union Vec3
+{
+    struct
+    {
+        float x, y, z;
+    }
+    float[3] e;
+}
+
+fn void test(Vec3 v)
+{
+}
+fn int main()
+{
+	test((Vec3){1,2,3});
+	return 0;
+}
+
+/* #expect: test.ll
+
+define void @test.test(<2 x float> %0, float %1) #0 {
+entry:
+  %v = alloca %Vec3, align 8
+  store <2 x float> %0, ptr %v, align 8
+  %ptradd = getelementptr inbounds i8, ptr %v, i64 8
+  store float %1, ptr %ptradd, align 8
+  ret void
+}
+
+define i32 @main() #0 {
+entry:
+  %literal = alloca %Vec3, align 4
+  %coerce = alloca %Vec3, align 8
+  call void @llvm.memcpy.p0.p0.i32(ptr align 4 %literal, ptr align 4 @.__const, i32 12, i1 false)
+  call void @llvm.memcpy.p0.p0.i32(ptr align 8 %coerce, ptr align 4 %literal, i32 12, i1 false)
+  %lo = load <2 x float>, ptr %coerce, align 8
+  %ptradd = getelementptr inbounds i8, ptr %coerce, i64 8
+  %hi = load float, ptr %ptradd, align 8
+  call void @test.test(<2 x float> %lo, float %hi)
+  ret i32 0
+}
+
+