Hi echristo, dblaikie,
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.
Why? 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.
Eric, do you know whether the local variable trick is necessary for GDB
compatibility?
REPOSITORY
rL LLVM
http://reviews.llvm.org/D9329
Files:
lib/CodeGen/CGDebugInfo.cpp
test/CodeGenCXX/debug-info-anon-union-vars.cpp
Index: lib/CodeGen/CGDebugInfo.cpp
===================================================================
--- lib/CodeGen/CGDebugInfo.cpp
+++ lib/CodeGen/CGDebugInfo.cpp
@@ -2835,31 +2835,6 @@
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.
Index: test/CodeGenCXX/debug-info-anon-union-vars.cpp
===================================================================
--- test/CodeGenCXX/debug-info-anon-union-vars.cpp
+++ test/CodeGenCXX/debug-info-anon-union-vars.cpp
@@ -21,8 +21,26 @@
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]],
EMAIL PREFERENCES
http://reviews.llvm.org/settings/panel/emailpreferences/
Index: lib/CodeGen/CGDebugInfo.cpp
===================================================================
--- lib/CodeGen/CGDebugInfo.cpp
+++ lib/CodeGen/CGDebugInfo.cpp
@@ -2835,31 +2835,6 @@
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.
Index: test/CodeGenCXX/debug-info-anon-union-vars.cpp
===================================================================
--- test/CodeGenCXX/debug-info-anon-union-vars.cpp
+++ test/CodeGenCXX/debug-info-anon-union-vars.cpp
@@ -21,8 +21,26 @@
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]],
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