arm64: Save func results before struct args

In gfunc_call(), structure members are loaded into registers during
argument handling.
This operation may overwrite previous function call results stored in
registers (e.g., s0). To prevent this, we must save function call
results to the stack before processing structure arguments.

Author: kbkpbot

arm64-gen.c

@@ -1101,6 +1101,9 @@ ST_FUNC void gfunc_call(int nb_args)
             // value in floating-point registers
             if ((vtop->type.t & VT_BTYPE) == VT_STRUCT) {
                 uint32_t j, sz, n = arm64_hfa(&vtop->type, &sz);
+                // save regs because struct may overwrite previous func call result
+                save_regs(0);
+
                 vtop->type.t = VT_PTR;
                 gaddrof();
                 gv(RC_R30);

tests/tests2/137_funcall_struct_args.c

@@ -0,0 +1,23 @@
+#include <stdio.h>
+
+// arm64-gen.c: gfunc_call() Second pass when struct args may overwrite previous func call result
+struct vec {
+        float x;
+        float y;
+};
+
+void bug(float x, float y) {
+    printf("x=%f\ny=%f\n", x, y);
+}
+
+float dot(struct vec v) {
+    return 999.5;
+}
+
+void main(void) {
+        struct vec a;
+        a.x = 33.0f;
+        a.y = 77.0f;
+        bug(dot(a), dot(a));
+}
+

tests/tests2/137_funcall_struct_args.expect

@@ -0,0 +1,2 @@
+x=999.500000
+y=999.500000