Extract mir_opt_level to a method and use Option to be able to know if the value is provided or not

compiler/rustc_mir/src/transform/const_goto.rs

@@ -28,7 +28,7 @@ pub struct ConstGoto;
 
 impl<'tcx> MirPass<'tcx> for ConstGoto {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        if tcx.sess.opts.debugging_opts.mir_opt_level < 3 {
+        if tcx.sess.mir_opt_level() < 3 {
             return;
         }
         trace!("Running ConstGoto on {:?}", body.source);

compiler/rustc_mir/src/transform/const_prop.rs

@@ -725,7 +725,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
             return None;
         }
 
-        if self.tcx.sess.opts.debugging_opts.mir_opt_level >= 3 {
+        if self.tcx.sess.mir_opt_level() >= 3 {
             self.eval_rvalue_with_identities(rvalue, place)
         } else {
             self.use_ecx(|this| this.ecx.eval_rvalue_into_place(rvalue, place))
@@ -903,7 +903,7 @@ 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.mir_opt_level();
 
         if mir_opt_level == 0 {
             return false;
@@ -1073,7 +1073,7 @@ 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.mir_opt_level() >= 2 {
             self.propagate_operand(operand)
         }
     }

compiler/rustc_mir/src/transform/deduplicate_blocks.rs

@@ -16,7 +16,7 @@ pub struct DeduplicateBlocks;
 
 impl<'tcx> MirPass<'tcx> for DeduplicateBlocks {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        if tcx.sess.opts.debugging_opts.mir_opt_level < 3 {
+        if tcx.sess.mir_opt_level() < 3 {
             return;
         }
         debug!("Running DeduplicateBlocks on `{:?}`", body.source);

compiler/rustc_mir/src/transform/dest_prop.rs

@@ -129,7 +129,7 @@ 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.mir_opt_level() <= 1 {
             return;
         }
 

compiler/rustc_mir/src/transform/early_otherwise_branch.rs

@@ -26,7 +26,7 @@ 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.mir_opt_level() < 2 {
             return;
         }
         trace!("running EarlyOtherwiseBranch on {:?}", body.source);

compiler/rustc_mir/src/transform/inline.rs

@@ -52,7 +52,7 @@ crate fn is_enabled(tcx: TyCtxt<'_>) -> bool {
         return enabled;
     }
 
-    tcx.sess.opts.debugging_opts.mir_opt_level >= 2
+    tcx.sess.mir_opt_level() >= 2
 }
 
 impl<'tcx> MirPass<'tcx> for Inline {

compiler/rustc_mir/src/transform/match_branches.rs

@@ -40,7 +40,7 @@ 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.mir_opt_level() <= 1 {
             return;
         }
 

compiler/rustc_mir/src/transform/mod.rs

@@ -475,7 +475,7 @@ 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.mir_opt_level();
 
     // 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

compiler/rustc_mir/src/transform/multiple_return_terminators.rs

@@ -10,7 +10,7 @@ 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.mir_opt_level() < 3 {
             return;
         }
 

compiler/rustc_mir/src/transform/nrvo.rs

@@ -34,7 +34,7 @@ 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.mir_opt_level() == 0 {
             return;
         }
 

compiler/rustc_mir/src/transform/unreachable_prop.rs

@@ -12,7 +12,7 @@ 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.mir_opt_level() < 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;

compiler/rustc_session/src/config.rs

@@ -1938,21 +1938,23 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
             Some(SymbolManglingVersion::V0) => {}
         }
 
-        if debugging_opts.mir_opt_level > 1 {
-            // Functions inlined during MIR transform can, at best, make it impossible to
-            // effectively cover inlined functions, and, at worst, break coverage map generation
-            // during LLVM codegen. For example, function counter IDs are only unique within a
-            // function. Inlining after these counters are injected can produce duplicate counters,
-            // resulting in an invalid coverage map (and ICE); so this option combination is not
-            // allowed.
-            early_warn(
-                error_format,
-                &format!(
-                    "`-Z mir-opt-level={}` (or any level > 1) enables function inlining, which \
+        if let Some(mir_opt_level) = debugging_opts.mir_opt_level {
+            if mir_opt_level > 1 {
+                // Functions inlined during MIR transform can, at best, make it impossible to
+                // effectively cover inlined functions, and, at worst, break coverage map generation
+                // during LLVM codegen. For example, function counter IDs are only unique within a
+                // function. Inlining after these counters are injected can produce duplicate counters,
+                // resulting in an invalid coverage map (and ICE); so this option combination is not
+                // allowed.
+                early_warn(
+                    error_format,
+                    &format!(
+                        "`-Z mir-opt-level={}` (or any level > 1) enables function inlining, which \
                     is incompatible with `-Z instrument-coverage`. Inlining will be disabled.",
-                    debugging_opts.mir_opt_level,
-                ),
-            );
+                        mir_opt_level,
+                    ),
+                );
+            }
         }
     }
 

compiler/rustc_session/src/options.rs

@@ -999,8 +999,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
     mir_emit_retag: bool = (false, parse_bool, [TRACKED],
         "emit Retagging MIR statements, interpreted e.g., by miri; implies -Zmir-opt-level=0 \
         (default: no)"),
-    mir_opt_level: usize = (1, parse_uint, [TRACKED],
-        "MIR optimization level (0-3; default: 1)"),
+    mir_opt_level: Option<usize> = (None, parse_opt_uint, [TRACKED],
+        "MIR optimization level (0-3; default: Some(1) in non optimized builds and Some(2) in optimized builds)"),
     mutable_noalias: bool = (false, parse_bool, [TRACKED],
         "emit noalias metadata for mutable references (default: no)"),
     new_llvm_pass_manager: bool = (false, parse_bool, [TRACKED],

compiler/rustc_session/src/session.rs

@@ -640,6 +640,9 @@ impl Session {
     pub fn binary_dep_depinfo(&self) -> bool {
         self.opts.debugging_opts.binary_dep_depinfo
     }
+    pub fn mir_opt_level(&self) -> usize {
+        self.opts.debugging_opts.mir_opt_level.unwrap_or(1)
+    }
 
     /// Gets the features enabled for the current compilation session.
     /// DO NOT USE THIS METHOD if there is a TyCtxt available, as it circumvents