Improve warnings on incompatible options involving -Zinstrument-coverage

Adds checks for:

* `no_core` attribute
* explicitly-enabled `legacy` symbol mangling
* mir_opt_level > 1 (which enables inlining)

I removed code from the `Inline` MIR pass that forcibly disabled
inlining if `-Zinstrument-coverage` was set. The default `mir_opt_level`
does not enable inlining anyway. But if the level is explicitly set and
is greater than 1, I issue a warning.

The new warnings show up in tests, which is much better for diagnosing
potential option conflicts in these cases.

2 files changed, 15 insertions, 3 deletions

diff --git a/compiler/rustc_metadata/src/creader.rs b/compiler/rustc_metadata/src/creader.rs
index 33cbf0fb234..019ca5174a2 100644
--- a/compiler/rustc_metadata/src/creader.rs
+++ b/compiler/rustc_metadata/src/creader.rs
@@ -706,7 +706,7 @@ impl<'a> CrateLoader<'a> {
         self.inject_dependency_if(cnum, "a panic runtime", &|data| data.needs_panic_runtime());
     }
 
-    fn inject_profiler_runtime(&mut self) {
+    fn inject_profiler_runtime(&mut self, krate: &ast::Crate) {
         if (self.sess.opts.debugging_opts.instrument_coverage
             || self.sess.opts.debugging_opts.profile
             || self.sess.opts.cg.profile_generate.enabled())
@@ -714,6 +714,13 @@ impl<'a> CrateLoader<'a> {
         {
             info!("loading profiler");
 
+            if self.sess.contains_name(&krate.attrs, sym::no_core) {
+                self.sess.err(
+                    "`profiler_builtins` crate (required by compiler options) \
+                               is not compatible with crate attribute `#![no_core]`",
+                );
+            }
+
             let name = sym::profiler_builtins;
             let cnum = self.resolve_crate(name, DUMMY_SP, CrateDepKind::Implicit, None);
             let data = self.cstore.get_crate_data(cnum);
@@ -879,7 +886,7 @@ impl<'a> CrateLoader<'a> {
     }
 
     pub fn postprocess(&mut self, krate: &ast::Crate) {
-        self.inject_profiler_runtime();
+        self.inject_profiler_runtime(krate);
         self.inject_allocator_crate(krate);
         self.inject_panic_runtime(krate);
 
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index 46dd0df65e0..b0c75c1de9d 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -663,7 +663,12 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             no_builtins: tcx.sess.contains_name(&attrs, sym::no_builtins),
             panic_runtime: tcx.sess.contains_name(&attrs, sym::panic_runtime),
             profiler_runtime: tcx.sess.contains_name(&attrs, sym::profiler_runtime),
-            symbol_mangling_version: tcx.sess.opts.debugging_opts.symbol_mangling_version,
+            symbol_mangling_version: tcx
+                .sess
+                .opts
+                .debugging_opts
+                .symbol_mangling_version
+                .unwrap_or(SymbolManglingVersion::default()),
 
             crate_deps,
             dylib_dependency_formats,