LLVM: always add argument attributes to calls

These are needed for correctness. There's no reason to only add them for
function pointers.

closes #16290

src/codegen/llvm.zig

@@ -5324,8 +5324,8 @@ pub const FuncGen = struct {
             },
         };
 
-        if (callee_ty.zigTypeTag(mod) == .Pointer) {
-            // Add argument attributes for function pointer calls.
+        {
+            // Add argument attributes.
             it = iterateParamTypes(o, fn_info);
             it.llvm_index += @intFromBool(sret);
             it.llvm_index += @intFromBool(err_return_tracing);

test/c_abi/cfuncs.c

@@ -1034,3 +1034,20 @@ struct ByRef __attribute__((sysv_abi)) c_explict_sys_v(struct ByRef in) {
     return in;
 }
 #endif
+
+
+struct byval_tail_callsite_attr_Point {
+    double x;
+    double y;
+} Point;
+struct byval_tail_callsite_attr_Size {
+    double width;
+    double height;
+} Size;
+struct byval_tail_callsite_attr_Rect {
+    struct byval_tail_callsite_attr_Point origin;
+    struct byval_tail_callsite_attr_Size size;
+};
+double c_byval_tail_callsite_attr(struct byval_tail_callsite_attr_Rect in) {
+    return in.size.width;
+}

test/c_abi/main.zig

@@ -1216,3 +1216,58 @@ test "explicit Win64 calling convention" {
     const res = c_explict_sys_v(.{ .val = 1, .arr = undefined });
     try expect(res.val == 42);
 }
+
+const byval_tail_callsite_attr = struct {
+    const struct_Point = extern struct {
+        x: f64,
+        y: f64,
+    };
+    const struct_Size = extern struct {
+        width: f64,
+        height: f64,
+    };
+    const struct_Rect = extern struct {
+        origin: struct_Point,
+        size: struct_Size,
+    };
+
+    const Point = extern struct {
+        x: f64,
+        y: f64,
+    };
+
+    const Size = extern struct {
+        width: f64,
+        height: f64,
+    };
+
+    const MyRect = extern struct {
+        origin: Point,
+        size: Size,
+
+        fn run(self: MyRect) f64 {
+            return c_byval_tail_callsite_attr(cast(self));
+        }
+
+        fn cast(self: MyRect) struct_Rect {
+            return @bitCast(self);
+        }
+
+        extern fn c_byval_tail_callsite_attr(struct_Rect) f64;
+    };
+};
+
+test "byval tail callsite attribute" {
+    if (comptime builtin.cpu.arch.isMIPS()) return error.SkipZigTest;
+    if (comptime builtin.cpu.arch.isPPC()) return error.SkipZigTest;
+
+    // Originally reported at https://github.com/ziglang/zig/issues/16290
+    // the bug was that the extern function had the byval attribute, but
+    // zig did not put the byval attribute at the callsite. Some LLVM optimization
+    // passes would then pass undefined for that parameter.
+    var v: byval_tail_callsite_attr.MyRect = .{
+        .origin = .{ .x = 1, .y = 2 },
+        .size = .{ .width = 3, .height = 4 },
+    };
+    try expect(v.run() == 3.0);
+}