coverage: Don't store function_source_hash in BcbCounter::Counter

This shows one small benefit of separating `BcbCounter` from `CoverageKind`.
The function source hash will be the same for all counters within a function,
so instead of passing it through `CoverageCounters` and storing it in every
counter, we can just supply it during the final conversion to `CoverageKind`.

Author: Zalathar

compiler/rustc_mir_transform/src/coverage/counters.rs

@@ -20,7 +20,7 @@ use std::fmt::{self, Debug};
 /// BCB node or BCB edge.
 #[derive(Clone)]
 pub(super) enum BcbCounter {
-    Counter { function_source_hash: u64, id: CounterId },
+    Counter { id: CounterId },
     Expression { id: ExpressionId, lhs: Operand, op: Op, rhs: Operand },
 }
 
@@ -59,7 +59,6 @@ impl Debug for BcbCounter {
 /// Generates and stores coverage counter and coverage expression information
 /// associated with nodes/edges in the BCB graph.
 pub(super) struct CoverageCounters {
-    function_source_hash: u64,
     next_counter_id: CounterId,
     next_expression_id: ExpressionId,
 
@@ -81,11 +80,10 @@ pub(super) struct CoverageCounters {
 }
 
 impl CoverageCounters {
-    pub(super) fn new(function_source_hash: u64, basic_coverage_blocks: &CoverageGraph) -> Self {
+    pub(super) fn new(basic_coverage_blocks: &CoverageGraph) -> Self {
         let num_bcbs = basic_coverage_blocks.num_nodes();
 
         Self {
-            function_source_hash,
             next_counter_id: CounterId::START,
             next_expression_id: ExpressionId::START,
 
@@ -119,10 +117,7 @@ impl CoverageCounters {
     where
         F: Fn() -> Option<String>,
     {
-        let counter = BcbCounter::Counter {
-            function_source_hash: self.function_source_hash,
-            id: self.next_counter(),
-        };
+        let counter = BcbCounter::Counter { id: self.next_counter() };
         if self.debug_counters.is_enabled() {
             self.debug_counters.add_counter(&counter, (debug_block_label_fn)());
         }

compiler/rustc_mir_transform/src/coverage/mod.rs

@@ -106,6 +106,7 @@ struct Instrumentor<'a, 'tcx> {
     source_file: Lrc<SourceFile>,
     fn_sig_span: Span,
     body_span: Span,
+    function_source_hash: u64,
     basic_coverage_blocks: CoverageGraph,
     coverage_counters: CoverageCounters,
 }
@@ -137,7 +138,7 @@ impl<'a, 'tcx> Instrumentor<'a, 'tcx> {
 
         let function_source_hash = hash_mir_source(tcx, hir_body);
         let basic_coverage_blocks = CoverageGraph::from_mir(mir_body);
-        let coverage_counters = CoverageCounters::new(function_source_hash, &basic_coverage_blocks);
+        let coverage_counters = CoverageCounters::new(&basic_coverage_blocks);
 
         Self {
             pass_name,
@@ -146,6 +147,7 @@ impl<'a, 'tcx> Instrumentor<'a, 'tcx> {
             source_file,
             fn_sig_span,
             body_span,
+            function_source_hash,
             basic_coverage_blocks,
             coverage_counters,
         }
@@ -435,8 +437,8 @@ impl<'a, 'tcx> Instrumentor<'a, 'tcx> {
 
     fn make_mir_coverage_kind(&self, counter_kind: &BcbCounter) -> CoverageKind {
         match *counter_kind {
-            BcbCounter::Counter { function_source_hash, id } => {
-                CoverageKind::Counter { function_source_hash, id }
+            BcbCounter::Counter { id } => {
+                CoverageKind::Counter { function_source_hash: self.function_source_hash, id }
             }
             BcbCounter::Expression { id, lhs, op, rhs } => {
                 CoverageKind::Expression { id, lhs, op, rhs }

compiler/rustc_mir_transform/src/coverage/tests.rs

@@ -674,7 +674,7 @@ fn test_make_bcb_counters() {
                 ));
             }
         }
-        let mut coverage_counters = counters::CoverageCounters::new(0, &basic_coverage_blocks);
+        let mut coverage_counters = counters::CoverageCounters::new(&basic_coverage_blocks);
         coverage_counters
             .make_bcb_counters(&mut basic_coverage_blocks, &coverage_spans)
             .expect("should be Ok");