Tweak a few mir-opt tests instead of using -Clink-dead-code

src/bootstrap/src/core/build_steps/test.rs

@@ -1470,7 +1470,6 @@ impl Step for MirOpt {
         };
 
         if builder.config.cmd.bless() {
-            crate::utils::cc_detect::find_target(builder, self.compiler.host);
             // All that we really need to do is cover all combinations of 32/64-bit and unwind/abort,
             // but while we're at it we might as well flex our cross-compilation support. This
             // selection covers all our tier 1 operating systems and architectures using only tier

src/tools/compiletest/src/runtest.rs

@@ -2468,7 +2468,6 @@ impl<'test> TestCx<'test> {
                     "-Zlint-mir",
                     "-Zdump-mir-exclude-pass-number",
                     "--crate-type=rlib",
-                    "-Clink-dead-code",
                 ]);
                 if let Some(pass) = &self.props.mir_unit_test {
                     rustc.args(&["-Zmir-opt-level=0", &format!("-Zmir-enable-passes=+{}", pass)]);

tests/mir-opt/fn_ptr_shim.rs

@@ -5,7 +5,7 @@
 // (as only `FnDef` and `FnPtr` callees are allowed in MIR).
 
 // EMIT_MIR core.ops-function-Fn-call.AddMovesForPackedDrops.before.mir
-fn main() {
+pub fn main() {
     call(noop as fn());
 }
 

tests/mir-opt/retag.rs

@@ -28,7 +28,7 @@ impl Drop for Test {
 
 // EMIT_MIR retag.main.SimplifyCfg-elaborate-drops.after.mir
 // EMIT_MIR retag.main-{closure#0}.SimplifyCfg-elaborate-drops.after.mir
-fn main() {
+pub fn main() {
     let mut x = 0;
     {
         let v = Test(0).foo(&mut x); // just making sure we do not panic when there is a tuple struct ctor

tests/mir-opt/slice_drop_shim.rs

@@ -1,6 +1,8 @@
 // skip-filecheck
-// compile-flags: -Zmir-opt-level=0
+// compile-flags: -Zmir-opt-level=0 -Clink-dead-code
-
+// mir-opt tests are always built as rlibs so that they seamlessly cross-compile,
+// so this test only produces MIR for the drop_in_place we're looking for
+// if we use -Clink-dead-code.
 
 // EMIT_MIR core.ptr-drop_in_place.[String].AddMovesForPackedDrops.before.mir
 fn main() {

tests/mir-opt/unusual_item_types.rs

@@ -23,7 +23,7 @@ enum E {
     V = 5,
 }
 
-fn main() {
+pub fn main() {
     let f = Test::X as fn(usize) -> Test;
 // EMIT_MIR core.ptr-drop_in_place.Vec_i32_.AddMovesForPackedDrops.before.mir
     let v = Vec::<i32>::new();