coverage: Defer part of counter-creation until codegen

compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/covfun.rs

@@ -54,7 +54,7 @@ pub(crate) fn prepare_covfun_record<'tcx>(
     let fn_cov_info = tcx.instance_mir(instance.def).function_coverage_info.as_deref()?;
     let ids_info = tcx.coverage_ids_info(instance.def)?;
 
-    let expressions = prepare_expressions(fn_cov_info, ids_info, is_used);
+    let expressions = prepare_expressions(ids_info, is_used);
 
     let mut covfun = CovfunRecord {
         mangled_function_name: tcx.symbol_name(instance).name,
@@ -76,11 +76,7 @@ pub(crate) fn prepare_covfun_record<'tcx>(
 }
 
 /// Convert the function's coverage-counter expressions into a form suitable for FFI.
-fn prepare_expressions(
-    fn_cov_info: &FunctionCoverageInfo,
-    ids_info: &CoverageIdsInfo,
-    is_used: bool,
-) -> Vec<ffi::CounterExpression> {
+fn prepare_expressions(ids_info: &CoverageIdsInfo, is_used: bool) -> Vec<ffi::CounterExpression> {
     // If any counters or expressions were removed by MIR opts, replace their
     // terms with zero.
     let counter_for_term = |term| {
@@ -95,7 +91,7 @@ fn prepare_expressions(
     // producing the final coverage map, so there's no need to do the same
     // thing on the Rust side unless we're confident we can do much better.
     // (See `CounterExpressionsMinimizer` in `CoverageMappingWriter.cpp`.)
-    fn_cov_info
+    ids_info
         .expressions
         .iter()
         .map(move |&Expression { lhs, op, rhs }| ffi::CounterExpression {
@@ -142,8 +138,7 @@ fn fill_region_tables<'tcx>(
         // If the mapping refers to counters/expressions that were removed by
         // MIR opts, replace those occurrences with zero.
         let counter_for_bcb = |bcb: BasicCoverageBlock| -> ffi::Counter {
-            let term =
-                fn_cov_info.term_for_bcb[bcb].expect("every BCB in a mapping was given a term");
+            let term = ids_info.term_for_bcb[bcb].expect("every BCB in a mapping was given a term");
             let term = if is_zero_term(term) { CovTerm::Zero } else { term };
             ffi::Counter::from_term(term)
         };