Simplify test and make it more reliable

The new `rmake`-content asserts the exact assembly sequence for the loop
preventing false-negatives if some instructions would change and thus
the label offset might need to change.

tests/run-make/avr-rjmp-offset/avr-rjmp-offsets.rs

@@ -1,7 +1,7 @@
 //! This test case is a `#![no_core]`-version of the MVCE presented in #129301.
 //!
-//! The function [`delay()`] is minimized and does not actually contain a loop
-//! in order to remove the need for additional lang items.
+//! The function [`delay()`] is removed, as it is not necessary to trigger the
+//! wrong behavior and would require some additional lang items.
 #![feature(no_core, lang_items, intrinsics, rustc_attrs, asm_experimental_arch)]
 #![no_core]
 #![no_main]
@@ -22,18 +22,10 @@ pub fn main() -> ! {
     // sions did place it after the first loop instruction, causing unsoundness)
     loop {
         unsafe { ptr::write_volatile(port_b, 1) };
-        delay(500_0000);
         unsafe { ptr::write_volatile(port_b, 2) };
-        delay(500_0000);
     }
 }
 
-#[inline(never)]
-#[no_mangle]
-fn delay(_: u32) {
-    unsafe { asm!("nop") };
-}
-
 // FIXME: replace with proper minicore once available (#130693)
 mod minicore {
     #[lang = "sized"]

tests/run-make/avr-rjmp-offset/rmake.rs

@@ -19,9 +19,31 @@ fn main() {
         .output("compiled")
         .run();
 
-    llvm_objdump()
-        .disassemble()
-        .input("compiled")
-        .run()
-        .assert_stdout_contains_regex(r"rjmp.*\.-14");
+    let disassembly = llvm_objdump().disassemble().input("compiled").run().stdout_utf8();
+
+    // search for the following instruction sequence:
+    // ```disassembly
+    // 00000080 <main>:
+    // 80: 81 e0         ldi     r24, 0x1
+    // 82: 92 e0         ldi     r25, 0x2
+    // 84: 85 b9         out     0x5, r24
+    // 86: 95 b9         out     0x5, r25
+    // 88: fd cf         rjmp    .-6
+    // ```
+    // This matches on all instructions, since the size of the instructions be-
+    // fore the relative jump has an impact on the label offset. Old versions
+    // of the Rust compiler did produce a label `rjmp .-4` (misses the first
+    // instruction in the loop).
+    disassembly
+        .trim()
+        .lines()
+        .skip_while(|&line| !line.contains("<main>"))
+        .skip(1)
+        .zip(["ldi\t", "ldi\t", "out\t", "out\t", "rjmp\t.-4"])
+        .for_each(|(line, expected_instruction)| {
+            assert!(
+                line.contains(expected_instruction),
+                "expected instruction `{expected_instruction}`, got `{line}`"
+            );
+        });
 }