Rework MIR inlining debuginfo so function parameters show up in debuggers.

compiler/rustc_codegen_llvm/src/debuginfo/create_scope_map.rs

@@ -88,7 +88,7 @@ fn make_mir_scope<'ll, 'tcx>(
     let loc = cx.lookup_debug_loc(scope_data.span.lo());
     let file_metadata = file_metadata(cx, &loc.file);
 
-    let parent_dbg_scope = match scope_data.inlined {
+    let dbg_scope = match scope_data.inlined {
         Some((callee, _)) => {
             // FIXME(eddyb) this would be `self.monomorphize(&callee)`
             // if this is moved to `rustc_codegen_ssa::mir::debuginfo`.
@@ -102,17 +102,15 @@ fn make_mir_scope<'ll, 'tcx>(
                 cx.dbg_scope_fn(callee, callee_fn_abi, None)
             })
         }
-        None => parent_scope.dbg_scope,
-    };
-
-    let dbg_scope = unsafe {
-        llvm::LLVMRustDIBuilderCreateLexicalBlock(
-            DIB(cx),
-            parent_dbg_scope,
-            file_metadata,
-            loc.line,
-            loc.col,
-        )
+        None => unsafe {
+            llvm::LLVMRustDIBuilderCreateLexicalBlock(
+                DIB(cx),
+                parent_scope.dbg_scope,
+                file_metadata,
+                loc.line,
+                loc.col,
+            )
+        },
     };
 
     let inlined_at = scope_data.inlined.map(|(_, callsite_span)| {

compiler/rustc_codegen_ssa/src/mir/debuginfo.rs

@@ -1,3 +1,4 @@
+use std::collections::hash_map::Entry;
 use std::ops::Range;
 
 use rustc_data_structures::fx::FxHashMap;
@@ -447,6 +448,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         }
 
         let mut per_local = IndexVec::from_elem(vec![], &self.mir.local_decls);
+        let mut params_seen: FxHashMap<_, Bx::DIVariable> = Default::default();
         for var in &self.mir.var_debug_info {
             let dbg_scope_and_span = if full_debug_info {
                 self.adjusted_span_and_dbg_scope(var.source_info)
@@ -491,7 +493,18 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     VariableKind::LocalVariable
                 };
 
-                self.cx.create_dbg_var(var.name, var_ty, dbg_scope, var_kind, span)
+                if let VariableKind::ArgumentVariable(arg_index) = var_kind {
+                    match params_seen.entry((dbg_scope, arg_index)) {
+                        Entry::Occupied(o) => o.get().clone(),
+                        Entry::Vacant(v) => v
+                            .insert(
+                                self.cx.create_dbg_var(var.name, var_ty, dbg_scope, var_kind, span),
+                            )
+                            .clone(),
+                    }
+                } else {
+                    self.cx.create_dbg_var(var.name, var_ty, dbg_scope, var_kind, span)
+                }
             });
 
             let fragment = if let Some(ref fragment) = var.composite {

compiler/rustc_codegen_ssa/src/mir/mod.rs

@@ -106,7 +106,7 @@ pub struct FunctionCx<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> {
     locals: locals::Locals<'tcx, Bx::Value>,
 
     /// All `VarDebugInfo` from the MIR body, partitioned by `Local`.
-    /// This is `None` if no var`#[non_exhaustive]`iable debuginfo/names are needed.
+    /// This is `None` if no variable debuginfo/names are needed.
     per_local_var_debug_info:
         Option<IndexVec<mir::Local, Vec<PerLocalVarDebugInfo<'tcx, Bx::DIVariable>>>>,
 

compiler/rustc_codegen_ssa/src/traits/backend.rs

@@ -1,4 +1,5 @@
 use std::any::Any;
+use std::hash::Hash;
 
 use rustc_ast::expand::allocator::AllocatorKind;
 use rustc_data_structures::fx::FxIndexMap;
@@ -30,7 +31,7 @@ pub trait BackendTypes {
 
     // FIXME(eddyb) find a common convention for all of the debuginfo-related
     // names (choose between `Dbg`, `Debug`, `DebugInfo`, `DI` etc.).
-    type DIScope: Copy;
+    type DIScope: Copy + Hash + PartialEq + Eq;
     type DILocation: Copy;
     type DIVariable: Copy;
 }

tests/codegen/debuginfo-inline-callsite-location.rs

@@ -9,13 +9,12 @@
 // CHECK:       tail call void @{{[A-Za-z0-9_]+4core6option13unwrap_failed}}
 // CHECK-SAME:  !dbg ![[#second_dbg:]]
 
-// CHECK-DAG:   ![[#func_dbg:]] = distinct !DISubprogram(name: "unwrap<i32>"
-// CHECK-DAG:   ![[#first_scope:]] = distinct !DILexicalBlock(scope: ![[#func_dbg]],
-// CHECK:       ![[#second_scope:]] = distinct !DILexicalBlock(scope: ![[#func_dbg]],
+// CHECK-DAG:   ![[#func_scope:]] = distinct !DISubprogram(name: "unwrap<i32>"
+// CHECK-DAG:   ![[#]] = !DILocalVariable(name: "self",{{( arg: 1,)?}} scope: ![[#func_scope]]
 // CHECK:       ![[#first_dbg]] = !DILocation(line: [[#]]
-// CHECK-SAME:  scope: ![[#first_scope]], inlinedAt: ![[#]])
+// CHECK-SAME:  scope: ![[#func_scope]], inlinedAt: ![[#]])
 // CHECK:       ![[#second_dbg]] = !DILocation(line: [[#]]
-// CHECK-SAME:  scope: ![[#second_scope]], inlinedAt: ![[#]])
+// CHECK-SAME:  scope: ![[#func_scope]], inlinedAt: ![[#]])
 
 #![crate_type = "lib"]
 

tests/codegen/inline-function-args-debug-info.rs

@@ -15,6 +15,7 @@ pub fn outer_function(x: usize, y: usize) -> usize {
 fn inner_function(aaaa: usize, bbbb: usize) -> usize {
     // CHECK: !DILocalVariable(name: "aaaa", arg: 1
     // CHECK-SAME: line: 15
+    // CHECK-NOT: !DILexicalBlock(
     // CHECK: !DILocalVariable(name: "bbbb", arg: 2
     // CHECK-SAME: line: 15
     aaaa + bbbb