coverage: Remove code for making expression copies of BCB counters

Now that coverage statements can have multiple code regions attached to them,
this code is never used.

Author: Zalathar

compiler/rustc_mir_transform/src/coverage/counters.rs

@@ -142,17 +142,6 @@ impl CoverageCounters {
         expression
     }
 
-    pub fn make_identity_counter(&mut self, counter_operand: Operand) -> BcbCounter {
-        let some_debug_block_label = if self.debug_counters.is_enabled() {
-            self.debug_counters.some_block_label(counter_operand).cloned()
-        } else {
-            None
-        };
-        self.make_expression(counter_operand, Op::Add, Operand::Zero, || {
-            some_debug_block_label.clone()
-        })
-    }
-
     /// Counter IDs start from one and go up.
     fn next_counter(&mut self) -> CounterId {
         let next = self.next_counter_id;

compiler/rustc_mir_transform/src/coverage/debug.rs

@@ -285,12 +285,6 @@ impl DebugCounters {
         }
     }
 
-    pub fn some_block_label(&self, operand: Operand) -> Option<&String> {
-        self.some_counters.as_ref().and_then(|counters| {
-            counters.get(&operand).and_then(|debug_counter| debug_counter.some_block_label.as_ref())
-        })
-    }
-
     pub fn format_counter(&self, counter_kind: &BcbCounter) -> String {
         match *counter_kind {
             BcbCounter::Counter { .. } => {

compiler/rustc_mir_transform/src/coverage/mod.rs

@@ -14,9 +14,7 @@ use self::spans::{CoverageSpan, CoverageSpans};
 
 use crate::MirPass;
 
-use rustc_data_structures::graph::WithNumNodes;
 use rustc_data_structures::sync::Lrc;
-use rustc_index::IndexVec;
 use rustc_middle::hir;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::mir::coverage::*;
@@ -296,22 +294,15 @@ impl<'a, 'tcx> Instrumentor<'a, 'tcx> {
         let body_span = self.body_span;
         let file_name = Symbol::intern(&self.source_file.name.prefer_remapped().to_string_lossy());
 
-        let mut bcb_counters = IndexVec::from_elem_n(None, self.basic_coverage_blocks.num_nodes());
-
         // Group the coverage spans by BCB, and process each BCB's spans at once.
         all_coverage_spans.sort_by_key(|span| span.bcb);
         for bcb_spans in all_coverage_spans.group_by(|a, b| a.bcb == b.bcb) {
             let bcb = bcb_spans[0].bcb;
 
-            let counter_kind = if let Some(&counter_operand) = bcb_counters[bcb].as_ref() {
-                self.coverage_counters.make_identity_counter(counter_operand)
-            } else if let Some(counter_kind) = self.coverage_counters.take_bcb_counter(bcb) {
-                bcb_counters[bcb] = Some(counter_kind.as_operand());
-                debug_used_expressions.add_expression_operands(&counter_kind);
-                counter_kind
-            } else {
+            let counter_kind = self.coverage_counters.take_bcb_counter(bcb).unwrap_or_else(|| {
                 bug!("Every BasicCoverageBlock should have a Counter or Expression");
-            };
+            });
+            debug_used_expressions.add_expression_operands(&counter_kind);
             graphviz_data.add_bcb_coverage_spans_with_counter(bcb, bcb_spans, &counter_kind);
 
             // Convert the coverage spans into a vector of code regions to be