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Debug Info: Represent local anonymous unions as anonymous unions 

in the debug info. This patch deletes a hack that emits the members
of local anonymous unions as local variables.

Besides being morally wrong, the existing representation using local
variables breaks internal assumptions about the local variables' storage
size.

Compiling

```
   void fn1() {
     union {
       int i;
       char c;
     };
     i = c;
   }

```

with -g -O3 -verify will cause the verifier to fail after SROA splits
the 32-bit storage for the "local variable" c into two pieces because the
second piece is clearly outside the 8-bit range that is expected for a
variable of type char. Given the choice I'd rather fix the debug
representation than weaken the verifier.

Debuggers generally already know how to deal with anonymous unions when
they are members of C++ record types, but they may have problems finding
the local anonymous struct members in the expression evaluator.

rdar://problem/20730771

llvm-svn: 236059
This commit is contained in:
Adrian Prantl 2015-04-28 23:01:24 +00:00
parent 89feff3b76
commit 0a4ddc180b
2 changed files with 18 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
clang/lib/CodeGen/CGDebugInfo.cpp
View File

@ -2835,31 +2835,6 @@ void CGDebugInfo::EmitDeclare(const VarDecl *VD, llvm::dwarf::Tag Tag,
return;
} else if (isa<VariableArrayType>(VD->getType()))
Expr.push_back(llvm::dwarf::DW_OP_deref);
} else if (const RecordType *RT = dyn_cast<RecordType>(VD->getType())) {
// If VD is an anonymous union then Storage represents value for
// all union fields.
const RecordDecl *RD = cast<RecordDecl>(RT->getDecl());
if (RD->isUnion() && RD->isAnonymousStructOrUnion()) {
for (const auto *Field : RD->fields()) {
llvm::MDType *FieldTy = getOrCreateType(Field->getType(), Unit);
StringRef FieldName = Field->getName();
// Ignore unnamed fields. Do not ignore unnamed records.
if (FieldName.empty() && !isa<RecordType>(Field->getType()))
continue;
// Use VarDecl's Tag, Scope and Line number.
auto *D = DBuilder.createLocalVariable(
Tag, Scope, FieldName, Unit, Line, FieldTy,
CGM.getLangOpts().Optimize, Flags, 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;
}
}
// Create the descriptor for the variable.

18
clang/test/CodeGenCXX/debug-info-anon-union-vars.cpp
View File

@ -21,8 +21,26 @@ int test_it() {
return (c == 1);
}
// This is not necessary (and actually harmful because it breaks IR assumptions)
// for local variables.
void foo() {
union {
int i;
char c;
};
i = 8;
}
// CHECK: [[FILE:.*]] = !MDFile(filename: "{{.*}}debug-info-anon-union-vars.cpp",
// CHECK: !MDGlobalVariable(name: "c",{{.*}} file: [[FILE]], line: 6,{{.*}} isLocal: true, isDefinition: true
// CHECK: !MDGlobalVariable(name: "d",{{.*}} file: [[FILE]], line: 6,{{.*}} isLocal: true, isDefinition: true
// CHECK: !MDGlobalVariable(name: "a",{{.*}} file: [[FILE]], line: 6,{{.*}} isLocal: true, isDefinition: true
// CHECK: !MDGlobalVariable(name: "b",{{.*}} file: [[FILE]], line: 6,{{.*}} isLocal: true, isDefinition: true
// CHECK: !MDLocalVariable(
// CHECK-NOT: name:
// CHECK: type: ![[UNION:[0-9]+]]
// CHECK: ![[UNION]] = !MDCompositeType(tag: DW_TAG_union_type,
// CHECK-NOT: name:
// CHECK: elements
// CHECK: !MDDerivedType(tag: DW_TAG_member, name: "i", scope: ![[UNION]],
// CHECK: !MDDerivedType(tag: DW_TAG_member, name: "c", scope: ![[UNION]],