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.

9 files changed, 21 insertions, 19 deletions

diff --git a/compiler/rustc_mir/src/transform/const_prop.rs b/compiler/rustc_mir/src/transform/const_prop.rs
index 1d949e020ed..49b1cf92600 100644
--- a/compiler/rustc_mir/src/transform/const_prop.rs
+++ b/compiler/rustc_mir/src/transform/const_prop.rs
@@ -22,6 +22,7 @@ use rustc_middle::ty::subst::{InternalSubsts, Subst};
 use rustc_middle::ty::{
     self, ConstInt, ConstKind, Instance, ParamEnv, ScalarInt, Ty, TyCtxt, TypeFoldable,
 };
+use rustc_session::config::MIR_OPT_LEVEL_DEFAULT;
 use rustc_session::lint;
 use rustc_span::{def_id::DefId, Span};
 use rustc_target::abi::{HasDataLayout, LayoutOf, Size, TargetDataLayout};
@@ -708,7 +709,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
             return None;
         }
 
-        if self.tcx.sess.opts.debugging_opts.mir_opt_level >= 3 {
+        if self.tcx.sess.opts.debugging_opts.mir_opt_level.unwrap_or(MIR_OPT_LEVEL_DEFAULT) >= 3 {
             self.eval_rvalue_with_identities(rvalue, place)
         } else {
             self.use_ecx(|this| this.ecx.eval_rvalue_into_place(rvalue, place))
@@ -886,7 +887,8 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
 
     /// Returns `true` if and only if this `op` should be const-propagated into.
     fn should_const_prop(&mut self, op: OpTy<'tcx>) -> bool {
-        let mir_opt_level = self.tcx.sess.opts.debugging_opts.mir_opt_level;
+        let mir_opt_level =
+            self.tcx.sess.opts.debugging_opts.mir_opt_level.unwrap_or(MIR_OPT_LEVEL_DEFAULT);
 
         if mir_opt_level == 0 {
             return false;
@@ -1056,7 +1058,7 @@ impl<'mir, 'tcx> MutVisitor<'tcx> for ConstPropagator<'mir, 'tcx> {
 
         // Only const prop copies and moves on `mir_opt_level=2` as doing so
         // currently slightly increases compile time in some cases.
-        if self.tcx.sess.opts.debugging_opts.mir_opt_level >= 2 {
+        if self.tcx.sess.opts.debugging_opts.mir_opt_level.unwrap_or(MIR_OPT_LEVEL_DEFAULT) >= 2 {
             self.propagate_operand(operand)
         }
     }
diff --git a/compiler/rustc_mir/src/transform/dest_prop.rs b/compiler/rustc_mir/src/transform/dest_prop.rs
index 46de5dba6e0..2363b6d58e1 100644
--- a/compiler/rustc_mir/src/transform/dest_prop.rs
+++ b/compiler/rustc_mir/src/transform/dest_prop.rs
@@ -115,6 +115,7 @@ use rustc_middle::mir::{
     Rvalue, Statement, StatementKind, Terminator, TerminatorKind,
 };
 use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_session::config::MIR_OPT_LEVEL_DEFAULT;
 
 // Empirical measurements have resulted in some observations:
 // - Running on a body with a single block and 500 locals takes barely any time
@@ -129,7 +130,7 @@ impl<'tcx> MirPass<'tcx> for DestinationPropagation {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         // Only run at mir-opt-level=2 or higher for now (we don't fix up debuginfo and remove
         // storage statements at the moment).
-        if tcx.sess.opts.debugging_opts.mir_opt_level <= 1 {
+        if tcx.sess.opts.debugging_opts.mir_opt_level.unwrap_or(MIR_OPT_LEVEL_DEFAULT) <= 1 {
             return;
         }
 
diff --git a/compiler/rustc_mir/src/transform/early_otherwise_branch.rs b/compiler/rustc_mir/src/transform/early_otherwise_branch.rs
index f91477911a4..023561923ee 100644
--- a/compiler/rustc_mir/src/transform/early_otherwise_branch.rs
+++ b/compiler/rustc_mir/src/transform/early_otherwise_branch.rs
@@ -1,6 +1,7 @@
 use crate::{transform::MirPass, util::patch::MirPatch};
 use rustc_middle::mir::*;
 use rustc_middle::ty::{Ty, TyCtxt};
+use rustc_session::config::MIR_OPT_LEVEL_DEFAULT;
 use std::fmt::Debug;
 
 use super::simplify::simplify_cfg;
@@ -26,7 +27,7 @@ pub struct EarlyOtherwiseBranch;
 
 impl<'tcx> MirPass<'tcx> for EarlyOtherwiseBranch {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        if tcx.sess.opts.debugging_opts.mir_opt_level < 2 {
+        if tcx.sess.opts.debugging_opts.mir_opt_level.unwrap_or(MIR_OPT_LEVEL_DEFAULT) < 2 {
             return;
         }
         trace!("running EarlyOtherwiseBranch on {:?}", body.source);
diff --git a/compiler/rustc_mir/src/transform/inline.rs b/compiler/rustc_mir/src/transform/inline.rs
index 4eeb8969bb1..1a927f9bf50 100644
--- a/compiler/rustc_mir/src/transform/inline.rs
+++ b/compiler/rustc_mir/src/transform/inline.rs
@@ -9,6 +9,7 @@ use rustc_middle::mir::visit::*;
 use rustc_middle::mir::*;
 use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::{self, ConstKind, Instance, InstanceDef, ParamEnv, Ty, TyCtxt};
+use rustc_session::config::MIR_OPT_LEVEL_DEFAULT;
 use rustc_span::{hygiene::ExpnKind, ExpnData, Span};
 use rustc_target::spec::abi::Abi;
 
@@ -37,15 +38,7 @@ struct CallSite<'tcx> {
 
 impl<'tcx> MirPass<'tcx> for Inline {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        if tcx.sess.opts.debugging_opts.mir_opt_level < 2 {
-            return;
-        }
-
-        if tcx.sess.opts.debugging_opts.instrument_coverage {
-            // The current implementation of source code coverage injects code region counters
-            // into the MIR, and assumes a 1-to-1 correspondence between MIR and source-code-
-            // based function.
-            debug!("function inlining is disabled when compiling with `instrument_coverage`");
+        if tcx.sess.opts.debugging_opts.mir_opt_level.unwrap_or(MIR_OPT_LEVEL_DEFAULT) < 2 {
             return;
         }
 
diff --git a/compiler/rustc_mir/src/transform/match_branches.rs b/compiler/rustc_mir/src/transform/match_branches.rs
index 53eeecc780f..e28e3f59a5e 100644
--- a/compiler/rustc_mir/src/transform/match_branches.rs
+++ b/compiler/rustc_mir/src/transform/match_branches.rs
@@ -1,6 +1,7 @@
 use crate::transform::MirPass;
 use rustc_middle::mir::*;
 use rustc_middle::ty::TyCtxt;
+use rustc_session::config::MIR_OPT_LEVEL_DEFAULT;
 
 pub struct MatchBranchSimplification;
 
@@ -38,7 +39,7 @@ pub struct MatchBranchSimplification;
 
 impl<'tcx> MirPass<'tcx> for MatchBranchSimplification {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        if tcx.sess.opts.debugging_opts.mir_opt_level <= 1 {
+        if tcx.sess.opts.debugging_opts.mir_opt_level.unwrap_or(MIR_OPT_LEVEL_DEFAULT) <= 1 {
             return;
         }
 
diff --git a/compiler/rustc_mir/src/transform/mod.rs b/compiler/rustc_mir/src/transform/mod.rs
index e86d11e248f..039dfe2c0d5 100644
--- a/compiler/rustc_mir/src/transform/mod.rs
+++ b/compiler/rustc_mir/src/transform/mod.rs
@@ -10,6 +10,7 @@ use rustc_middle::mir::visit::Visitor as _;
 use rustc_middle::mir::{traversal, Body, ConstQualifs, MirPhase, Promoted};
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, TyCtxt, TypeFoldable};
+use rustc_session::config::MIR_OPT_LEVEL_DEFAULT;
 use rustc_span::{Span, Symbol};
 use std::borrow::Cow;
 
@@ -373,7 +374,7 @@ fn run_post_borrowck_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tc
 }
 
 fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-    let mir_opt_level = tcx.sess.opts.debugging_opts.mir_opt_level;
+    let mir_opt_level = tcx.sess.opts.debugging_opts.mir_opt_level.unwrap_or(MIR_OPT_LEVEL_DEFAULT);
 
     // Lowering generator control-flow and variables has to happen before we do anything else
     // to them. We run some optimizations before that, because they may be harder to do on the state
diff --git a/compiler/rustc_mir/src/transform/multiple_return_terminators.rs b/compiler/rustc_mir/src/transform/multiple_return_terminators.rs
index 617086622cc..de4aee7ddbc 100644
--- a/compiler/rustc_mir/src/transform/multiple_return_terminators.rs
+++ b/compiler/rustc_mir/src/transform/multiple_return_terminators.rs
@@ -5,12 +5,13 @@ use crate::transform::{simplify, MirPass};
 use rustc_index::bit_set::BitSet;
 use rustc_middle::mir::*;
 use rustc_middle::ty::TyCtxt;
+use rustc_session::config::MIR_OPT_LEVEL_DEFAULT;
 
 pub struct MultipleReturnTerminators;
 
 impl<'tcx> MirPass<'tcx> for MultipleReturnTerminators {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        if tcx.sess.opts.debugging_opts.mir_opt_level < 3 {
+        if tcx.sess.opts.debugging_opts.mir_opt_level.unwrap_or(MIR_OPT_LEVEL_DEFAULT) < 3 {
             return;
         }
 
diff --git a/compiler/rustc_mir/src/transform/nrvo.rs b/compiler/rustc_mir/src/transform/nrvo.rs
index ce02fb261df..6e1dc03b9cb 100644
--- a/compiler/rustc_mir/src/transform/nrvo.rs
+++ b/compiler/rustc_mir/src/transform/nrvo.rs
@@ -5,6 +5,7 @@ use rustc_index::bit_set::HybridBitSet;
 use rustc_middle::mir::visit::{MutVisitor, NonUseContext, PlaceContext, Visitor};
 use rustc_middle::mir::{self, BasicBlock, Local, Location};
 use rustc_middle::ty::TyCtxt;
+use rustc_session::config::MIR_OPT_LEVEL_DEFAULT;
 
 use crate::transform::MirPass;
 
@@ -34,7 +35,7 @@ pub struct RenameReturnPlace;
 
 impl<'tcx> MirPass<'tcx> for RenameReturnPlace {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut mir::Body<'tcx>) {
-        if tcx.sess.opts.debugging_opts.mir_opt_level == 0 {
+        if tcx.sess.opts.debugging_opts.mir_opt_level.unwrap_or(MIR_OPT_LEVEL_DEFAULT) == 0 {
             return;
         }
 
diff --git a/compiler/rustc_mir/src/transform/unreachable_prop.rs b/compiler/rustc_mir/src/transform/unreachable_prop.rs
index e39c8656021..c9053ce81cd 100644
--- a/compiler/rustc_mir/src/transform/unreachable_prop.rs
+++ b/compiler/rustc_mir/src/transform/unreachable_prop.rs
@@ -7,12 +7,13 @@ use crate::transform::MirPass;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_middle::mir::*;
 use rustc_middle::ty::TyCtxt;
+use rustc_session::config::MIR_OPT_LEVEL_DEFAULT;
 
 pub struct UnreachablePropagation;
 
 impl MirPass<'_> for UnreachablePropagation {
     fn run_pass<'tcx>(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        if tcx.sess.opts.debugging_opts.mir_opt_level < 3 {
+        if tcx.sess.opts.debugging_opts.mir_opt_level.unwrap_or(MIR_OPT_LEVEL_DEFAULT) < 3 {
             // Enable only under -Zmir-opt-level=3 as in some cases (check the deeply-nested-opt
             // perf benchmark) LLVM may spend quite a lot of time optimizing the generated code.
             return;