Don't insert receiver NULL checks on GNUStep

crates/objc2/src/runtime/message_receiver.rs

@@ -154,6 +154,15 @@ mod msg_send_primitive {
         args: A,
     ) -> R {
         let msg_send_fn = R::MSG_SEND;
+        // Note: Modern Objective-C compilers have a workaround to ensure that
+        // messages to `nil` with a struct return produces `mem::zeroed()`,
+        // see:
+        // <https://www.sealiesoftware.com/blog/archive/2012/2/29/objc_explain_return_value_of_message_to_nil.html>
+        //
+        // We _could_ technically do something similar, but since we're
+        // disallowing messages to `nil` with `debug_assertions` enabled
+        // anyhow, and since Rust has a much stronger type-system that
+        // disallows NULL/nil in most cases, we won't bother supporting it.
         unsafe { A::__invoke(msg_send_fn, receiver, sel, args) }
     }
 
@@ -206,16 +215,12 @@ mod msg_send_primitive {
         sel: Sel,
         args: A,
     ) -> R {
-        // If `receiver` is NULL, objc_msg_lookup will return a standard C-method
-        // taking two arguments, the receiver and the selector. Transmuting and
-        // calling such a function with multiple parameters is UB, so instead we
-        // return NULL directly.
-        if receiver.is_null() {
-            // SAFETY: Caller guarantees that messages to NULL-receivers only
-            // return pointers, and a mem::zeroed pointer is just a NULL-pointer.
-            return unsafe { mem::zeroed() };
-        }
-
+        // If `receiver` is NULL, objc_msg_lookup will return a standard
+        // C-method taking two arguments, the receiver and the selector.
+        //
+        // Transmuting and calling such a function with multiple parameters is
+        // safe as long as the return value is a primitive (and e.g. not a big
+        // struct or array).
         let msg_send_fn = unsafe { ffi::objc_msg_lookup(receiver.cast(), sel.as_ptr()) };
         let msg_send_fn = unwrap_msg_send_fn(msg_send_fn);
         unsafe { A::__invoke(msg_send_fn, receiver, sel, args) }
@@ -228,11 +233,6 @@ mod msg_send_primitive {
         sel: Sel,
         args: A,
     ) -> R {
-        if receiver.is_null() {
-            // SAFETY: Same as in `send`.
-            return unsafe { mem::zeroed() };
-        }
-
         let superclass: *const AnyClass = superclass;
         let sup = ffi::objc_super {
             receiver: receiver.cast(),

crates/test-assembly/crates/test_msg_send_error/expected/gnustep-x86.s

@@ -223,15 +223,13 @@ error_init:
 	push	esi
 	sub	esp, 16
 	mov	esi, dword ptr [esp + 32]
+	mov	edi, dword ptr [esp + 36]
 	call	.L5$pb
 .L5$pb:
 	pop	ebx
 	mov	dword ptr [esp + 12], 0
 .Ltmp5:
 	add	ebx, offset _GLOBAL_OFFSET_TABLE_+(.Ltmp5-.L5$pb)
-	test	esi, esi
-	je	.LBB5_1
-	mov	edi, dword ptr [esp + 36]
 	sub	esp, 8
 	push	edi
 	push	esi
@@ -244,26 +242,22 @@ error_init:
 	call	eax
 	add	esp, 16
 	test	eax, eax
-	je	.LBB5_4
+	je	.LBB5_2
 	mov	edx, eax
 	xor	eax, eax
-.LBB5_6:
+.LBB5_3:
 	add	esp, 16
 	pop	esi
 	pop	edi
 	pop	ebx
 	ret
-.LBB5_1:
-	xor	ecx, ecx
-	jmp	.LBB5_5
-.LBB5_4:
+.LBB5_2:
 	mov	ecx, dword ptr [esp + 12]
-.LBB5_5:
 	lea	edx, [ebx + .Lanon.[ID].6@GOTOFF]
 	call	SYM(objc2[CRATE_ID]::__macro_helpers::msg_send_id::encountered_error::<objc2[CRATE_ID]::runtime::AnyObject>, 0)
 	mov	edx, eax
 	mov	eax, 1
-	jmp	.LBB5_6
+	jmp	.LBB5_3
 .Lfunc_end5:
 	.size	error_init, .Lfunc_end5-error_init
 

crates/test-assembly/crates/test_msg_send_error/expected/gnustep-x86_64.s

@@ -156,30 +156,24 @@ error_init:
 	push	r14
 	push	rbx
 	push	rax
-	mov	qword ptr [rsp], 0
-	test	rdi, rdi
-	je	.LBB5_1
 	mov	rbx, rsi
 	mov	r14, rdi
+	mov	qword ptr [rsp], 0
 	call	qword ptr [rip + objc_msg_lookup@GOTPCREL]
 	mov	rdx, rsp
 	mov	rdi, r14
 	mov	rsi, rbx
 	call	rax
 	test	rax, rax
-	je	.LBB5_4
+	je	.LBB5_2
 	mov	rdx, rax
 	xor	eax, eax
 	add	rsp, 8
 	pop	rbx
 	pop	r14
 	ret
-.LBB5_1:
-	xor	edi, edi
-	jmp	.LBB5_5
-.LBB5_4:
+.LBB5_2:
 	mov	rdi, qword ptr [rsp]
-.LBB5_5:
 	lea	rsi, [rip + .Lanon.[ID].6]
 	call	SYM(objc2[CRATE_ID]::__macro_helpers::msg_send_id::encountered_error::<objc2[CRATE_ID]::runtime::AnyObject>, 0)
 	mov	rdx, rax

crates/test-assembly/crates/test_msg_send_id/expected/gnustep-x86.s

@@ -155,14 +155,12 @@ handle_init:
 	push	edi
 	push	esi
 	mov	esi, dword ptr [esp + 16]
+	mov	edi, dword ptr [esp + 20]
 	call	.L4$pb
 .L4$pb:
 	pop	ebx
 .Ltmp4:
 	add	ebx, offset _GLOBAL_OFFSET_TABLE_+(.Ltmp4-.L4$pb)
-	test	esi, esi
-	je	.LBB4_2
-	mov	edi, dword ptr [esp + 20]
 	sub	esp, 8
 	push	edi
 	push	esi
@@ -176,12 +174,6 @@ handle_init:
 	pop	edi
 	pop	ebx
 	ret
-.LBB4_2:
-	xor	eax, eax
-	pop	esi
-	pop	edi
-	pop	ebx
-	ret
 .Lfunc_end4:
 	.size	handle_init, .Lfunc_end4-handle_init
 
@@ -193,15 +185,13 @@ handle_init_fallible:
 	push	ebx
 	push	edi
 	push	esi
-	mov	esi, dword ptr [esp + 16]
 	mov	edi, dword ptr [esp + 20]
+	mov	esi, dword ptr [esp + 16]
 	call	.L5$pb
 .L5$pb:
 	pop	ebx
 .Ltmp5:
 	add	ebx, offset _GLOBAL_OFFSET_TABLE_+(.Ltmp5-.L5$pb)
-	test	esi, esi
-	je	.LBB5_2
 	sub	esp, 8
 	push	edi
 	push	esi
@@ -212,12 +202,12 @@ handle_init_fallible:
 	call	eax
 	add	esp, 16
 	test	eax, eax
-	je	.LBB5_2
+	je	.LBB5_1
 	pop	esi
 	pop	edi
 	pop	ebx
 	ret
-.LBB5_2:
+.LBB5_1:
 	sub	esp, 4
 	lea	eax, [ebx + .Lanon.[ID].3@GOTOFF]
 	push	eax
@@ -234,28 +224,28 @@ handle_init_fallible:
 	.p2align	4, 0x90
 	.type	handle_alloc_init,@function
 handle_alloc_init:
+	push	ebp
 	push	ebx
 	push	edi
 	push	esi
-	mov	esi, dword ptr [esp + 16]
-	mov	edi, dword ptr [esp + 20]
+	sub	esp, 12
+	mov	edi, dword ptr [esp + 40]
+	mov	esi, dword ptr [esp + 32]
+	mov	ebp, dword ptr [esp + 36]
 	call	.L6$pb
 .L6$pb:
 	pop	ebx
 .Ltmp6:
 	add	ebx, offset _GLOBAL_OFFSET_TABLE_+(.Ltmp6-.L6$pb)
 	sub	esp, 8
-	push	edi
+	push	ebp
 	push	esi
 	call	objc_msg_lookup@PLT
 	add	esp, 8
-	push	edi
+	push	ebp
 	push	esi
 	call	eax
 	add	esp, 16
-	test	eax, eax
-	je	.LBB6_2
-	mov	edi, dword ptr [esp + 24]
 	mov	esi, eax
 	sub	esp, 8
 	push	edi
@@ -265,16 +255,11 @@ handle_alloc_init:
 	push	edi
 	push	esi
 	call	eax
-	add	esp, 16
-	pop	esi
-	pop	edi
-	pop	ebx
-	ret
-.LBB6_2:
-	xor	eax, eax
+	add	esp, 28
 	pop	esi
 	pop	edi
 	pop	ebx
+	pop	ebp
 	ret
 .Lfunc_end6:
 	.size	handle_alloc_init, .Lfunc_end6-handle_alloc_init

crates/test-assembly/crates/test_msg_send_id/expected/gnustep-x86_64.s

@@ -103,8 +103,6 @@ handle_alloc_fallible:
 	.p2align	4, 0x90
 	.type	handle_init,@function
 handle_init:
-	test	rdi, rdi
-	je	.LBB4_1
 	push	r14
 	push	rbx
 	push	rax
@@ -117,9 +115,6 @@ handle_init:
 	pop	rbx
 	pop	r14
 	jmp	rax
-.LBB4_1:
-	xor	eax, eax
-	ret
 .Lfunc_end4:
 	.size	handle_init, .Lfunc_end4-handle_init
 
@@ -133,21 +128,17 @@ handle_init_fallible:
 	push	rax
 	mov	rbx, rsi
 	mov	r14, rdi
-	test	rdi, rdi
-	je	.LBB5_2
-	mov	rdi, r14
-	mov	rsi, rbx
 	call	qword ptr [rip + objc_msg_lookup@GOTPCREL]
 	mov	rdi, r14
 	mov	rsi, rbx
 	call	rax
 	test	rax, rax
-	je	.LBB5_2
+	je	.LBB5_1
 	add	rsp, 8
 	pop	rbx
 	pop	r14
 	ret
-.LBB5_2:
+.LBB5_1:
 	lea	rdx, [rip + .Lanon.[ID].3]
 	mov	rdi, r14
 	mov	rsi, rbx
@@ -163,32 +154,29 @@ handle_init_fallible:
 handle_alloc_init:
 	push	r15
 	push	r14
+	push	r12
 	push	rbx
+	push	rax
 	mov	rbx, rdx
 	mov	r14, rsi
 	mov	r15, rdi
-	call	qword ptr [rip + objc_msg_lookup@GOTPCREL]
+	mov	r12, qword ptr [rip + objc_msg_lookup@GOTPCREL]
+	call	r12
 	mov	rdi, r15
 	mov	rsi, r14
 	call	rax
-	test	rax, rax
-	je	.LBB6_1
 	mov	r14, rax
 	mov	rdi, rax
 	mov	rsi, rbx
-	call	qword ptr [rip + objc_msg_lookup@GOTPCREL]
+	call	r12
 	mov	rdi, r14
 	mov	rsi, rbx
+	add	rsp, 8
 	pop	rbx
+	pop	r12
 	pop	r14
 	pop	r15
 	jmp	rax
-.LBB6_1:
-	xor	eax, eax
-	pop	rbx
-	pop	r14
-	pop	r15
-	ret
 .Lfunc_end6:
 	.size	handle_alloc_init, .Lfunc_end6-handle_alloc_init