r236125 - Debug Info: Represent local anonymous unions as anonymous unions

[Adrian Prantl]

Author: adrian
Date: Wed Apr 29 11:52:31 2015
New Revision: 236125

URL: http://llvm.org/viewvc/llvm-project?rev=236125&view=rev
Log:
Debug Info: Represent local anonymous unions as anonymous unions
and as artificial local variables in the debug info.

This is a follow-up to r236059. We can't get rid of the local variables
entirely because the gdb buildbot depends on them, but we can mark them
as artificial while still emitting the correct debug info. As I learned
from review comments other compilers also follow this model.

A paired commit in LLVM temporarily relaxes the debug info verifier to
not check the integrity of DW_OP_bit_pieces of artificial variables.

rdar://problem/20730771

Modified:
    cfe/trunk/lib/CodeGen/CGDebugInfo.cpp
    cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp

Modified: cfe/trunk/lib/CodeGen/CGDebugInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGDebugInfo.cpp?rev=236125&r1=236124&r2=236125&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CGDebugInfo.cpp (original)
+++ cfe/trunk/lib/CodeGen/CGDebugInfo.cpp Wed Apr 29 11:52:31 2015
@@ -2839,6 +2839,13 @@ void CGDebugInfo::EmitDeclare(const VarD
     // all union fields.
     const RecordDecl *RD = cast<RecordDecl>(RT->getDecl());
     if (RD->isUnion() && RD->isAnonymousStructOrUnion()) {
+      // GDB has trouble finding local variables in anonymous unions, so we emit
+      // artifical local variables for each of the members.
+      //
+      // FIXME: Remove this code as soon as GDB supports this.
+      // The debug info verifier in LLVM operates based on the assumption that a
+      // variable has the same size as its storage and we had to disable the check
+      // for artificial variables.
       for (const auto *Field : RD->fields()) {
         llvm::DIType *FieldTy = getOrCreateType(Field->getType(), Unit);
         StringRef FieldName = Field->getName();
@@ -2850,14 +2857,14 @@ void CGDebugInfo::EmitDeclare(const VarD
         // Use VarDecl's Tag, Scope and Line number.
         auto *D = DBuilder.createLocalVariable(
             Tag, Scope, FieldName, Unit, Line, FieldTy,
-            CGM.getLangOpts().Optimize, Flags, ArgNo);
+            CGM.getLangOpts().Optimize, Flags | llvm::DINode::FlagArtificial,
+            ArgNo);
 
         // Insert an llvm.dbg.declare into the current block.
         DBuilder.insertDeclare(Storage, D, DBuilder.createExpression(Expr),
                                llvm::DebugLoc::get(Line, Column, Scope),
                                Builder.GetInsertBlock());
       }
-      return;
     }
   }
 

Modified: cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp?rev=236125&r1=236124&r2=236125&view=diff
==============================================================================
--- cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp (original)
+++ cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp Wed Apr 29 11:52:31 2015
@@ -21,8 +21,26 @@ int test_it() {
   return (c == 1);
 }
 
+void foo() {
+  union {
+    int i;
+    char c;
+  };
+  i = 8;
+}
+
 // CHECK: [[FILE:.*]] = !DIFile(filename: "{{.*}}debug-info-anon-union-vars.cpp",
 // CHECK: !DIGlobalVariable(name: "c",{{.*}} file: [[FILE]], line: 6,{{.*}} isLocal: true, isDefinition: true
 // CHECK: !DIGlobalVariable(name: "d",{{.*}} file: [[FILE]], line: 6,{{.*}} isLocal: true, isDefinition: true
 // CHECK: !DIGlobalVariable(name: "a",{{.*}} file: [[FILE]], line: 6,{{.*}} isLocal: true, isDefinition: true
 // CHECK: !DIGlobalVariable(name: "b",{{.*}} file: [[FILE]], line: 6,{{.*}} isLocal: true, isDefinition: true
+// CHECK: !DILocalVariable(tag: DW_TAG_auto_variable, name: "i", {{.*}}, flags: DIFlagArtificial
+// CHECK: !DILocalVariable(tag: DW_TAG_auto_variable, name: "c", {{.*}}, flags: DIFlagArtificial
+// CHECK: !DILocalVariable(
+// CHECK-NOT: name:
+// CHECK: type: ![[UNION:[0-9]+]]
+// CHECK: ![[UNION]] = !DICompositeType(tag: DW_TAG_union_type,
+// CHECK-NOT: name:
+// CHECK: elements
+// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "i", scope: ![[UNION]],
+// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "c", scope: ![[UNION]],