Fix coverage ICEs (unreachable-cov-only, spanview wrong body)

compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs

@@ -61,7 +61,7 @@ pub fn finalize<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>) {
 
     // Encode coverage mappings and generate function records
     let mut function_data = Vec::new();
-    for (instance, function_coverage) in function_coverage_map {
+    for (instance, mut function_coverage) in function_coverage_map {
         debug!("Generate function coverage for {}, {:?}", cx.codegen_unit.name(), instance);
         let mangled_function_name = tcx.symbol_name(instance).to_string();
         let source_hash = function_coverage.source_hash();

compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs

@@ -244,15 +244,9 @@ fn add_unused_function_coverage(
 ) {
     let tcx = cx.tcx;
 
-    let mut function_coverage = FunctionCoverage::unused(tcx, instance);
-    for (index, &code_region) in tcx.covered_code_regions(def_id).iter().enumerate() {
-        if index == 0 {
-            // Insert at least one real counter so the LLVM CoverageMappingReader will find expected
-            // definitions.
-            function_coverage.add_counter(UNUSED_FUNCTION_COUNTER_ID, code_region.clone());
-        } else {
-            function_coverage.add_unreachable_region(code_region.clone());
-        }
+    let mut function_coverage = FunctionCoverage::unused(instance);
+    for &code_region in tcx.covered_code_regions(def_id).iter() {
+        function_coverage.add_unreachable_region(code_region.clone());
     }
 
     if let Some(coverage_context) = cx.coverage_context() {

compiler/rustc_codegen_ssa/src/coverageinfo/map.rs

@@ -28,6 +28,7 @@ pub struct Expression {
 /// only whitespace or comments). According to LLVM Code Coverage Mapping documentation, "A count
 /// for a gap area is only used as the line execution count if there are no other regions on a
 /// line."
+#[derive(Debug)]
 pub struct FunctionCoverage<'tcx> {
     instance: Instance<'tcx>,
     source_hash: u64,
@@ -40,30 +41,34 @@ pub struct FunctionCoverage<'tcx> {
 impl<'tcx> FunctionCoverage<'tcx> {
     /// Creates a new set of coverage data for a used (called) function.
     pub fn new(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) -> Self {
-        Self::create(tcx, instance, true)
-    }
-
-    /// Creates a new set of coverage data for an unused (never called) function.
-    pub fn unused(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) -> Self {
-        Self::create(tcx, instance, false)
-    }
-
-    fn create(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>, is_used: bool) -> Self {
         let coverageinfo = tcx.coverageinfo(instance.def_id());
         debug!(
-            "FunctionCoverage::new(instance={:?}) has coverageinfo={:?}. is_used={}",
-            instance, coverageinfo, is_used
+            "FunctionCoverage::new(instance={:?}) has coverageinfo={:?}",
+            instance, coverageinfo
         );
         Self {
             instance,
             source_hash: 0, // will be set with the first `add_counter()`
-            is_used,
+            is_used: true,
             counters: IndexVec::from_elem_n(None, coverageinfo.num_counters as usize),
             expressions: IndexVec::from_elem_n(None, coverageinfo.num_expressions as usize),
             unreachable_regions: Vec::new(),
         }
     }
 
+    /// Creates a new set of coverage data for an unused (never called) function.
+    pub fn unused(instance: Instance<'tcx>) -> Self {
+        debug!("FunctionCoverage::unused(instance={:?})", instance);
+        Self {
+            instance,
+            source_hash: 0, // will be set with the first `add_counter()`
+            is_used: false,
+            counters: IndexVec::from_elem_n(None, CounterValueReference::START.as_usize()),
+            expressions: IndexVec::new(),
+            unreachable_regions: Vec::new(),
+        }
+    }
+
     /// Returns true for a used (called) function, and false for an unused function.
     pub fn is_used(&self) -> bool {
         self.is_used
@@ -142,13 +147,33 @@ impl<'tcx> FunctionCoverage<'tcx> {
     /// associated `Regions` (from which the LLVM-specific `CoverageMapGenerator` will create
     /// `CounterMappingRegion`s.
     pub fn get_expressions_and_counter_regions<'a>(
-        &'a self,
+        &'a mut self,
     ) -> (Vec<CounterExpression>, impl Iterator<Item = (Counter, &'a CodeRegion)>) {
-        assert!(
-            self.source_hash != 0 || !self.is_used,
-            "No counters provided the source_hash for used function: {:?}",
-            self.instance
-        );
+        if self.source_hash == 0 {
+            // Either this `FunctionCoverage` is _not_ used (created via
+            // `unused()`, or the function had all statements removed, including
+            // all `Counter`s.
+            //
+            // Dead blocks (removed during MIR transform, typically because
+            // const evaluation can determine that the block will never be
+            // called) are removed before codegen, but any coverage statements
+            // are replaced by `Coverage::unreachable` statements at the top of
+            // the MIR CFG.
+            debug!("No counters provided the source_hash for used function:\n{:?}", self);
+            assert_eq!(
+                self.expressions.len(),
+                0,
+                "Expressions (from MIR) without counters: {:?}",
+                self.instance
+            );
+            // If there are `Unreachable` code regions, but no `Counter`s, we
+            // need to add at least one Counter, because LLVM seems to require
+            // it.
+            if let Some(unreachable_code_region) = self.unreachable_regions.pop() {
+                // Replace any one of the `Unreachable`s with a counter.
+                self.counters.push(Some(unreachable_code_region));
+            }
+        }
 
         let counter_regions = self.counter_regions();
         let (counter_expressions, expression_regions) = self.expressions_with_regions();

compiler/rustc_mir/src/transform/coverage/debug.rs

@@ -120,6 +120,7 @@ use rustc_index::vec::Idx;
 use rustc_middle::mir::coverage::*;
 use rustc_middle::mir::{self, BasicBlock, TerminatorKind};
 use rustc_middle::ty::TyCtxt;
+use rustc_span::Span;
 
 use std::iter;
 use std::lazy::SyncOnceCell;
@@ -636,6 +637,7 @@ pub(super) fn dump_coverage_spanview(
     mir_body: &mir::Body<'tcx>,
     basic_coverage_blocks: &CoverageGraph,
     pass_name: &str,
+    body_span: Span,
     coverage_spans: &Vec<CoverageSpan>,
 ) {
     let mir_source = mir_body.source;
@@ -647,7 +649,7 @@ pub(super) fn dump_coverage_spanview(
     let crate_name = tcx.crate_name(def_id.krate);
     let item_name = tcx.def_path(def_id).to_filename_friendly_no_crate();
     let title = format!("{}.{} - Coverage Spans", crate_name, item_name);
-    spanview::write_document(tcx, def_id, span_viewables, &title, &mut file)
+    spanview::write_document(tcx, body_span, span_viewables, &title, &mut file)
         .expect("Unexpected IO error dumping coverage spans as HTML");
 }
 

compiler/rustc_mir/src/transform/coverage/mod.rs

@@ -95,7 +95,7 @@ impl<'tcx> MirPass<'tcx> for InstrumentCoverage {
 
         trace!("InstrumentCoverage starting for {:?}", mir_source.def_id());
         Instrumentor::new(&self.name(), tcx, mir_body).inject_counters();
-        trace!("InstrumentCoverage starting for {:?}", mir_source.def_id());
+        trace!("InstrumentCoverage done for {:?}", mir_source.def_id());
     }
 }
 
@@ -116,25 +116,7 @@ impl<'a, 'tcx> Instrumentor<'a, 'tcx> {
         let def_id = mir_body.source.def_id();
         let (some_fn_sig, hir_body) = fn_sig_and_body(tcx, def_id);
 
-        let mut body_span = hir_body.value.span;
-
-        if tcx.is_closure(def_id) {
-            // If the MIR function is a closure, and if the closure body span
-            // starts from a macro, but it's content is not in that macro, try
-            // to find a non-macro callsite, and instrument the spans there
-            // instead.
-            loop {
-                let expn_data = body_span.ctxt().outer_expn_data();
-                if expn_data.is_root() {
-                    break;
-                }
-                if let ExpnKind::Macro(..) = expn_data.kind {
-                    body_span = expn_data.call_site;
-                } else {
-                    break;
-                }
-            }
-        }
+        let body_span = get_body_span(tcx, hir_body, mir_body);
 
         let source_file = source_map.lookup_source_file(body_span.lo());
         let fn_sig_span = match some_fn_sig.filter(|fn_sig| {
@@ -144,6 +126,15 @@ impl<'a, 'tcx> Instrumentor<'a, 'tcx> {
             Some(fn_sig) => fn_sig.span.with_hi(body_span.lo()),
             None => body_span.shrink_to_lo(),
         };
+
+        debug!(
+            "instrumenting {}: {:?}, fn sig span: {:?}, body span: {:?}",
+            if tcx.is_closure(def_id) { "closure" } else { "function" },
+            def_id,
+            fn_sig_span,
+            body_span
+        );
+
         let function_source_hash = hash_mir_source(tcx, hir_body);
         let basic_coverage_blocks = CoverageGraph::from_mir(mir_body);
         Self {
@@ -160,19 +151,11 @@ impl<'a, 'tcx> Instrumentor<'a, 'tcx> {
 
     fn inject_counters(&'a mut self) {
         let tcx = self.tcx;
-        let source_map = tcx.sess.source_map();
         let mir_source = self.mir_body.source;
         let def_id = mir_source.def_id();
         let fn_sig_span = self.fn_sig_span;
         let body_span = self.body_span;
 
-        debug!(
-            "instrumenting {:?}, fn sig span: {}, body span: {}",
-            def_id,
-            source_map.span_to_string(fn_sig_span),
-            source_map.span_to_string(body_span)
-        );
-
         let mut graphviz_data = debug::GraphvizData::new();
         let mut debug_used_expressions = debug::UsedExpressions::new();
 
@@ -204,6 +187,7 @@ impl<'a, 'tcx> Instrumentor<'a, 'tcx> {
                 self.mir_body,
                 &self.basic_coverage_blocks,
                 self.pass_name,
+                body_span,
                 &coverage_spans,
             );
         }
@@ -560,6 +544,35 @@ fn fn_sig_and_body<'tcx>(
     (hir::map::fn_sig(hir_node), tcx.hir().body(fn_body_id))
 }
 
+fn get_body_span<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    hir_body: &rustc_hir::Body<'tcx>,
+    mir_body: &mut mir::Body<'tcx>,
+) -> Span {
+    let mut body_span = hir_body.value.span;
+    let def_id = mir_body.source.def_id();
+
+    if tcx.is_closure(def_id) {
+        // If the MIR function is a closure, and if the closure body span
+        // starts from a macro, but it's content is not in that macro, try
+        // to find a non-macro callsite, and instrument the spans there
+        // instead.
+        loop {
+            let expn_data = body_span.ctxt().outer_expn_data();
+            if expn_data.is_root() {
+                break;
+            }
+            if let ExpnKind::Macro(..) = expn_data.kind {
+                body_span = expn_data.call_site;
+            } else {
+                break;
+            }
+        }
+    }
+
+    body_span
+}
+
 fn hash_mir_source<'tcx>(tcx: TyCtxt<'tcx>, hir_body: &'tcx rustc_hir::Body<'tcx>) -> u64 {
     let mut hcx = tcx.create_no_span_stable_hashing_context();
     hash(&mut hcx, &hir_body.value).to_smaller_hash()

compiler/rustc_mir/src/transform/coverage/spans.rs

@@ -527,17 +527,25 @@ impl<'a, 'tcx> CoverageSpans<'a, 'tcx> {
                     .iter()
                     .enumerate()
                     .filter_map(move |(index, statement)| {
-                        filtered_statement_span(statement, self.body_span).map(
-                            |(span, expn_span)| {
-                                CoverageSpan::for_statement(
-                                    statement, span, expn_span, bcb, bb, index,
-                                )
-                            },
-                        )
+                        filtered_statement_span(statement).map(|span| {
+                            CoverageSpan::for_statement(
+                                statement,
+                                function_source_span(span, self.body_span),
+                                span,
+                                bcb,
+                                bb,
+                                index,
+                            )
+                        })
                     })
-                    .chain(filtered_terminator_span(data.terminator(), self.body_span).map(
-                        |(span, expn_span)| CoverageSpan::for_terminator(span, expn_span, bcb, bb),
-                    ))
+                    .chain(filtered_terminator_span(data.terminator()).map(|span| {
+                        CoverageSpan::for_terminator(
+                            function_source_span(span, self.body_span),
+                            span,
+                            bcb,
+                            bb,
+                        )
+                    }))
             })
             .collect()
     }
@@ -792,13 +800,9 @@ impl<'a, 'tcx> CoverageSpans<'a, 'tcx> {
     }
 }
 
-/// See `function_source_span()` for a description of the two returned spans.
-/// If the MIR `Statement` is not contributive to computing coverage spans,
-/// returns `None`.
-pub(super) fn filtered_statement_span(
-    statement: &'a Statement<'tcx>,
-    body_span: Span,
-) -> Option<(Span, Span)> {
+/// If the MIR `Statement` has a span contributive to computing coverage spans,
+/// return it; otherwise return `None`.
+pub(super) fn filtered_statement_span(statement: &'a Statement<'tcx>) -> Option<Span> {
     match statement.kind {
         // These statements have spans that are often outside the scope of the executed source code
         // for their parent `BasicBlock`.
@@ -835,18 +839,14 @@ pub(super) fn filtered_statement_span(
         | StatementKind::LlvmInlineAsm(_)
         | StatementKind::Retag(_, _)
         | StatementKind::AscribeUserType(_, _) => {
-            Some(function_source_span(statement.source_info.span, body_span))
+            Some(statement.source_info.span)
         }
     }
 }
 
-/// See `function_source_span()` for a description of the two returned spans.
-/// If the MIR `Terminator` is not contributive to computing coverage spans,
-/// returns `None`.
-pub(super) fn filtered_terminator_span(
-    terminator: &'a Terminator<'tcx>,
-    body_span: Span,
-) -> Option<(Span, Span)> {
+/// If the MIR `Terminator` has a span contributive to computing coverage spans,
+/// return it; otherwise return `None`.
+pub(super) fn filtered_terminator_span(terminator: &'a Terminator<'tcx>) -> Option<Span> {
     match terminator.kind {
         // These terminators have spans that don't positively contribute to computing a reasonable
         // span of actually executed source code. (For example, SwitchInt terminators extracted from
@@ -870,7 +870,7 @@ pub(super) fn filtered_terminator_span(
                     span = span.with_lo(constant.span.lo());
                 }
             }
-            Some(function_source_span(span, body_span))
+            Some(span)
         }
 
         // Retain spans from all other terminators
@@ -881,28 +881,20 @@ pub(super) fn filtered_terminator_span(
         | TerminatorKind::GeneratorDrop
         | TerminatorKind::FalseUnwind { .. }
         | TerminatorKind::InlineAsm { .. } => {
-            Some(function_source_span(terminator.source_info.span, body_span))
+            Some(terminator.source_info.span)
         }
     }
 }
 
-/// Returns two spans from the given span (the span associated with a
-/// `Statement` or `Terminator`):
-///
-///   1. An extrapolated span (pre-expansion[^1]) corresponding to a range within
-///      the function's body source. This span is guaranteed to be contained
-///      within, or equal to, the `body_span`. If the extrapolated span is not
-///      contained within the `body_span`, the `body_span` is returned.
-///   2. The actual `span` value from the `Statement`, before expansion.
-///
-/// Only the first span is used when computing coverage code regions. The second
-/// span is useful if additional expansion data is needed (such as to look up
-/// the macro name for a composed span within that macro).)
+/// Returns an extrapolated span (pre-expansion[^1]) corresponding to a range
+/// within the function's body source. This span is guaranteed to be contained
+/// within, or equal to, the `body_span`. If the extrapolated span is not
+/// contained within the `body_span`, the `body_span` is returned.
 ///
-/// [^1]Expansions result from Rust syntax including macros, syntactic
-/// sugar, etc.).
+/// [^1]Expansions result from Rust syntax including macros, syntactic sugar,
+/// etc.).
 #[inline]
-fn function_source_span(span: Span, body_span: Span) -> (Span, Span) {
+pub(super) fn function_source_span(span: Span, body_span: Span) -> Span {
     let original_span = original_sp(span, body_span).with_ctxt(body_span.ctxt());
-    (if body_span.contains(original_span) { original_span } else { body_span }, span)
+    if body_span.contains(original_span) { original_span } else { body_span }
 }