coverage. Fix DropGlue instances might cause rustc panic when mcdc is enabled

Author: zhuyunxing

compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs

@@ -9,6 +9,7 @@ use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
 use rustc_llvm::RustString;
 use rustc_middle::bug;
 use rustc_middle::mir::coverage::CoverageKind;
+use rustc_middle::mir::{Statement, StatementKind};
 use rustc_middle::ty::layout::HasTyCtxt;
 use rustc_middle::ty::Instance;
 use rustc_target::abi::{Align, Size};
@@ -92,16 +93,39 @@ impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
 
 impl<'tcx> CoverageInfoBuilderMethods<'tcx> for Builder<'_, '_, 'tcx> {
     fn init_coverage(&mut self, instance: Instance<'tcx>) {
-        let Some(function_coverage_info) =
-            self.tcx.instance_mir(instance.def).function_coverage_info.as_deref()
-        else {
+        let mir_body = self.tcx.instance_mir(instance.def);
+
+        let Some(function_coverage_info) = mir_body.function_coverage_info.as_deref() else {
             return;
         };
 
         // If there are no MC/DC bitmaps to set up, return immediately.
         if function_coverage_info.mcdc_bitmap_bits == 0 {
             return;
         }
+        let is_mcdc_instrument = |statement: &Statement<'_>| {
+            let StatementKind::Coverage(coverage_kind) = &statement.kind else {
+                return false;
+            };
+            matches!(
+                coverage_kind,
+                CoverageKind::TestVectorBitmapUpdate { .. }
+                    | CoverageKind::CondBitmapUpdate { .. }
+                    | CoverageKind::CondBitmapReset { .. }
+            )
+        };
+        // Mir bodies of instances like `DropGlue` might be cloned from other instances' and removed some basic blocks.
+        // Such instances likely have same `function_coverage_info` as primary instances but have no coverage statements.
+        // No need to initialize mcdc parameters for this kind of instances.
+        if !mir_body
+            .basic_blocks
+            .iter()
+            .map(|bb| bb.statements.iter())
+            .flatten()
+            .any(is_mcdc_instrument)
+        {
+            return;
+        }
 
         let fn_name = self.get_pgo_func_name_var(instance);
         let hash = self.const_u64(function_coverage_info.function_source_hash);