From 6cb9d7ae53fd5a6a0f79d56de82b425cb003947c Mon Sep 17 00:00:00 2001
From: Benjamin Oldenburg <benjamin.oldenburg@ordis.co.th>
Date: Mon, 16 Mar 2026 01:09:10 +0700
Subject: [PATCH] arm64: use union type tags in HFA classification

---
 arm64-gen.c                  | 20 +-------------------
 tests/tests2/73_arm64.c      | 15 +++++++++++++++
 tests/tests2/73_arm64.expect |  4 ++++
 3 files changed, 20 insertions(+), 19 deletions(-)

diff --git a/arm64-gen.c b/arm64-gen.c
index 9cd76943..ea5b64eb 100644
--- a/arm64-gen.c
+++ b/arm64-gen.c
@@ -778,28 +778,10 @@ static int arm64_hfa_aux(CType *type, int *fsize, int num)
         return num + 1;
     }
     else if ((type->t & VT_BTYPE) == VT_STRUCT) {
-        int is_struct = 1; /* assume struct, check if union */
         Sym *field;
         if (!type->ref)
             return -1;
-        /* A union has all fields at offset 0, a struct has increasing offsets */
-        for (field = type->ref->next; field; field = field->next)
-            if (field->c != 0) {
-                is_struct = 1;
-                break;
-            }
-        /* If all fields are at offset 0 and there's more than one field, it's a union */
-        if (type->ref->next && type->ref->next->next && !type->ref->next->c) {
-            /* Check if all fields are at offset 0 (union) */
-            int all_zero = 1;
-            for (field = type->ref->next; field; field = field->next)
-                if (field->c != 0) {
-                    all_zero = 0;
-                    break;
-                }
-            is_struct = !all_zero;
-        }
-        if (is_struct) {
+        if (!IS_UNION(type->t)) {
             int num0 = num;
             for (field = type->ref->next; field; field = field->next) {
                 if (field->c != (num - num0) * *fsize)
diff --git a/tests/tests2/73_arm64.c b/tests/tests2/73_arm64.c
index 855c4767..16be1047 100644
--- a/tests/tests2/73_arm64.c
+++ b/tests/tests2/73_arm64.c
@@ -38,6 +38,11 @@ struct hfa32 { long double a, b; } hfa32 = { 32.1, 32.2 };
 struct hfa33 { long double a, b, c; } hfa33 = { 33.1, 33.2, 33.3 };
 struct hfa34 { long double a, b, c, d; } hfa34 = { 34.1, 34.2, 34.3, 34.4 };
 
+struct empty { };
+/* Keep the top-level offsets at zero without changing the type into a union. */
+struct hfae12 { struct empty e; struct hfa12 h; } hfae12 = { { }, { 112.1, 112.2 } };
+struct hfae22 { struct empty e; struct hfa22 h; } hfae22 = { { }, { 122.1, 122.2 } };
+
 void fa_s1(struct s1 a) { printf("%.1s\n", a.x); }
 void fa_s2(struct s2 a) { printf("%.2s\n", a.x); }
 void fa_s3(struct s3 a) { printf("%.3s\n", a.x); }
@@ -82,6 +87,10 @@ void fa_hfa33(struct hfa33 a)
 { printf("%.1Lf %.1Lf %.1Lf\n", a.a, a.b, a.c); }
 void fa_hfa34(struct hfa34 a)
 { printf("%.1Lf %.1Lf %.1Lf %.1Lf\n", a.a, a.b, a.c, a.d); }
+void fa_hfae12(struct hfae12 a)
+{ printf("%.1f %.1f\n", a.h.a, a.h.b); }
+void fa_hfae22(struct hfae22 a)
+{ printf("%.1f %.1f\n", a.h.a, a.h.b); }
 
 void fa1(struct s8 a, struct s9 b, struct s10 c, struct s11 d,
          struct s12 e, struct s13 f)
@@ -140,6 +149,8 @@ void arg(void)
     fa_hfa32(hfa32);
     fa_hfa33(hfa33);
     fa_hfa34(hfa34);
+    fa_hfae12(hfae12);
+    fa_hfae22(hfae22);
     fa1(s8, s9, s10, s11, s12, s13);
     fa2(s9, s10, s11, s12, s13, s14);
     fa3(hfa14, hfa23, hfa32);
@@ -178,6 +189,8 @@ struct hfa31 fr_hfa31(void) { return hfa31; }
 struct hfa32 fr_hfa32(void) { return hfa32; }
 struct hfa33 fr_hfa33(void) { return hfa33; }
 struct hfa34 fr_hfa34(void) { return hfa34; }
+struct hfae12 fr_hfae12(void) { return hfae12; }
+struct hfae22 fr_hfae22(void) { return hfae22; }
 
 void ret(void)
 {
@@ -228,6 +241,8 @@ void ret(void)
     printf("%.1Lf %.1Lf\n", fr_hfa32().a, fr_hfa32().b);
     printf("%.1Lf %.1Lf\n", fr_hfa33().a, fr_hfa33().c);
     printf("%.1Lf %.1Lf\n", fr_hfa34().a, fr_hfa34().d);
+    printf("%.1f %.1f\n", fr_hfae12().h.a, fr_hfae12().h.b);
+    printf("%.1f %.1f\n", fr_hfae22().h.a, fr_hfae22().h.b);
 }
 
 void*
diff --git a/tests/tests2/73_arm64.expect b/tests/tests2/73_arm64.expect
index 7bdebd30..7bc07500 100644
--- a/tests/tests2/73_arm64.expect
+++ b/tests/tests2/73_arm64.expect
@@ -28,6 +28,8 @@ cdefghijklmnopqrs
 32.1 32.1
 33.1 33.2 33.3
 34.1 34.2 34.3 34.4
+112.1 112.2
+122.1 122.2
 stu ABC JKL TUV 456 ghi
 ABC JKL TUV 456 ghi tuv
 14.1 14.4 23.1 23.3 32.1 32.2
@@ -62,6 +64,8 @@ cdefghijklmnopqrs
 32.1 32.2
 33.1 33.3
 34.1 34.4
+112.1 112.2
+122.1 122.2
 stdarg:
 ABCDEFGHI ABCDEFGHI ABCDEFGHI ABCDEFGHI ABCDEFGHI ABCDEFGHI
 lmnopqr ABCDEFGHI ABCDEFGHI ABCDEFGHI ABCDEFGHI ABCDEFGHI