Exclude global_asm from mir_keys

compiler/rustc_mir_transform/src/lib.rs

@@ -316,6 +316,10 @@ fn mir_keys(tcx: TyCtxt<'_>, (): ()) -> FxIndexSet<LocalDefId> {
     // All body-owners have MIR associated with them.
     let mut set: FxIndexSet<_> = tcx.hir_body_owners().collect();
 
+    // Remove the fake bodies for `global_asm!`, since they're not useful
+    // to be emitted (`--emit=mir`) or encoded (in metadata).
+    set.retain(|&def_id| !matches!(tcx.def_kind(def_id), DefKind::GlobalAsm));
+
     // Coroutine-closures (e.g. async closures) have an additional by-move MIR
     // body that isn't in the HIR.
     for body_owner in tcx.hir_body_owners() {

tests/ui/asm/global-asm-isnt-really-a-mir-body.rs

@@ -0,0 +1,23 @@
+//@ revisions: emit_mir instrument cfi
+
+// Make sure we don't try to emit MIR for it.
+//@[emit_mir] compile-flags: --emit=mir
+
+// Make sure we don't try to instrument it.
+//@[instrument] compile-flags: -Cinstrument-coverage -Zno-profiler-runtime
+//@[instrument] only-linux
+
+// Make sure we don't try to CFI encode it.
+//@[cfi] compile-flags: -Zsanitizer=cfi -Ccodegen-units=1 -Clto -Clink-dead-code=true
+//@[cfi] needs-sanitizer-cfi
+//@[cfi] no-prefer-dynamic
+
+//@ build-pass
+
+use std::arch::global_asm;
+
+fn foo() {}
+
+global_asm!("/* {} */", sym foo);
+
+fn main() {}