Merge pull request #38942 from mshockwave/dev-dbg-var-artificial

[DebugInfo] Prevent salvaged debug vars from being marked artificial

Author: mshockwave

lib/IRGen/IRGenDebugInfo.cpp

@@ -2543,6 +2543,23 @@ void IRGenDebugInfoImpl::emitDbgIntrinsic(
       !llvm::FindDbgDeclareUses(Storage).empty())
     return;
 
+  // Fragment DIExpression cannot cover the whole variable
+  // or going out-of-bound.
+  if (auto Fragment = Expr->getFragmentInfo())
+    if (auto VarSize = Var->getSizeInBits()) {
+      unsigned FragSize = Fragment->SizeInBits;
+      unsigned FragOffset = Fragment->OffsetInBits;
+      if (FragOffset + FragSize > *VarSize ||
+          FragSize == *VarSize) {
+        // Drop the fragment part
+        assert(Expr->isValid());
+        // Since this expression is valid, DW_OP_LLVM_fragment
+        // and its arguments must be the last 3 elements.
+        auto OrigElements = Expr->getElements();
+        Expr = DBuilder.createExpression(OrigElements.drop_back(3));
+      }
+    }
+
   // A dbg.declare is only meaningful if there is a single alloca for
   // the variable that is live throughout the function.
   if (auto *Alloca = dyn_cast<llvm::AllocaInst>(Storage)) {

lib/SILOptimizer/Utils/InstOptUtils.cpp

@@ -2119,8 +2119,7 @@ void swift::salvageDebugInfo(SILInstruction *I) {
               DestVal.getDefiningInstruction())) {
         if (auto VarInfo = ASI->getVarInfo())
           SILBuilder(SI, ASI->getDebugScope())
-              .createDebugValue(RegularLocation::getAutoGeneratedLocation(),
-                                SI->getSrc(), *VarInfo);
+              .createDebugValue(SI->getLoc(), SI->getSrc(), *VarInfo);
       }
   }
 }

test/DebugInfo/debug_info_expression.sil

@@ -8,6 +8,10 @@ struct MyStruct {
   var y: Builtin.Int64
 }
 
+struct SmallStruct {
+  var z : Builtin.Int64
+}
+
 sil_scope 1 { loc "file.swift":7:6 parent @test_fragment : $@convention(thin) () -> () }
 
 // Testing op_fragment w/ debug_value_addr
@@ -16,6 +20,8 @@ bb0:
   %2 = alloc_stack $MyStruct, var, name "my_struct", loc "file.swift":8:9, scope 1
   // CHECK: %[[MY_STRUCT:.+]] = alloca %{{.*}}MyStruct
   // CHECK: llvm.dbg.declare(metadata {{.*}}* %[[MY_STRUCT]], metadata ![[VAR_DECL_MD:[0-9]+]]
+  // CHECK: %[[SMALL_STRUCT:.+]] = alloca %{{.*}}SmallStruct
+  // CHECK: llvm.dbg.declare(metadata {{.*}}* %[[SMALL_STRUCT]], metadata ![[SMALL_VAR_DECL_MD:[0-9]+]]
   %3 = struct_element_addr %2 : $*MyStruct, #MyStruct.x, loc "file.swift":9:17, scope 1
   // CHECK: %[[FIELD_X:.*]] = getelementptr {{.*}} %[[MY_STRUCT]]
   // CHECK-SIL: debug_value_addr %{{[0-9]+}} : $*Builtin.Int64
@@ -25,6 +31,17 @@ bb0:
   // CHECK: llvm.dbg.value(metadata {{.*}}* %[[FIELD_X]], metadata ![[VAR_DECL_MD]]
   // CHECK-SAME:           !DIExpression(DW_OP_deref, DW_OP_LLVM_fragment, 0, 64)
   // CHECK-NOT:           ), !dbg ![[VAR_DECL_MD]]
+
+  %4 = alloc_stack $SmallStruct, var, name "small_struct", loc "file.swift":10:11, scope 1
+  %5 = struct_element_addr %4 : $*SmallStruct, #SmallStruct.z, loc "file.swift":11:13, scope 1
+  // CHECK: %[[FIELD_Z:.*]] = getelementptr {{.*}} %[[SMALL_STRUCT]]
+  // If the fragment covers the whole struct, we're not generating the
+  // DW_OP_LLVM_fragment part.
+  // CHECK: llvm.dbg.value(metadata {{.*}}* %[[FIELD_Z]], metadata ![[SMALL_VAR_DECL_MD]]
+  // CHECK-SAME:           !DIExpression(DW_OP_deref)
+  debug_value_addr %5 : $*Builtin.Int64, var, (name "small_struct", loc "file.swift":10:11, scope 1), type $SmallStruct, expr op_fragment:#SmallStruct.z, loc "file.swift":11:13, scope 1
+  dealloc_stack %4 : $*SmallStruct
+
   dealloc_stack %2 : $*MyStruct
   %r = tuple()
   return %r : $()

test/DebugInfo/sroa_mem2reg.sil

@@ -2,6 +2,8 @@
 // RUN: %target-sil-opt -enable-sil-verify-all -sil-print-debuginfo -sroa -mem2reg %s -o %t.sil
 // RUN: %FileCheck --check-prefix=CHECK-MEM2REG %s --input-file=%t.sil
 // RUN: %target-swiftc_driver -Xfrontend -disable-debugger-shadow-copies -g -emit-ir %t.sil | %FileCheck --check-prefix=CHECK-IR %s
+// RUN: %target-swiftc_driver -Xfrontend -disable-debugger-shadow-copies -g -c %t.sil -o %t.o
+// RUN: %llvm-dwarfdump --debug-info %t.o | %FileCheck --check-prefix=CHECK-DWARF %s
 sil_stage canonical
 
 import Builtin
@@ -78,3 +80,10 @@ bb0(%0 : $Int64, %1 : $Int64):
 // CHECK-IR-SAME:                            line: 7
 // CHECK-IR: ![[ARG2_MD]] = !DILocalVariable(name: "in_y", arg: 2
 // CHECK-IR-SAME:                            line: 7
+
+// CHECK-DWARF-LABEL:   DW_AT_name    ("foo")
+// CHECK-DWARF:       DW_TAG_variable
+// CHECK-DWARF:         DW_AT_name  ("my_struct")
+// Shouldn't be marked artificial
+// CHECK-DWARF-NOT:     DW_AT_artificial      (true)
+// CHECK-DWARF:       DW_TAG_{{.*}}