diff options
Diffstat (limited to 'clang/lib')
| -rw-r--r-- | clang/lib/CodeGen/CGDebugInfo.cpp | 38 |
1 files changed, 26 insertions, 12 deletions
diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp index c7637ef47d1..dbf6ae5dc8a 100644 --- a/clang/lib/CodeGen/CGDebugInfo.cpp +++ b/clang/lib/CodeGen/CGDebugInfo.cpp @@ -829,31 +829,45 @@ static bool hasCXXMangling(const TagDecl *TD, llvm::DICompileUnit *TheCU) { } } -// Determines if the tag declaration will require a type identifier. +// Determines if the debug info for this tag declaration needs a type +// identifier. The purpose of the unique identifier is to deduplicate type +// information for identical types across TUs. Because of the C++ one definition +// rule (ODR), it is valid to assume that the type is defined the same way in +// every TU and its debug info is equivalent. +// +// C does not have the ODR, and it is common for codebases to contain multiple +// different definitions of a struct with the same name in different TUs. +// Therefore, if the type doesn't have a C++ mangling, don't give it an +// identifer. Type information in C is smaller and simpler than C++ type +// information, so the increase in debug info size is negligible. +// +// If the type is not externally visible, it should be unique to the current TU, +// and should not need an identifier to participate in type deduplication. +// However, when emitting CodeView, the format internally uses these +// unique type name identifers for references between debug info. For example, +// the method of a class in an anonymous namespace uses the identifer to refer +// to its parent class. The Microsoft C++ ABI attempts to provide unique names +// for such types, so when emitting CodeView, always use identifiers for C++ +// types. This may create problems when attempting to emit CodeView when the MS +// C++ ABI is not in use. static bool needsTypeIdentifier(const TagDecl *TD, CodeGenModule &CGM, llvm::DICompileUnit *TheCU) { // We only add a type identifier for types with C++ name mangling. if (!hasCXXMangling(TD, TheCU)) return false; - // CodeView types with C++ mangling need a type identifier. - if (CGM.getCodeGenOpts().EmitCodeView) - return true; - // Externally visible types with C++ mangling need a type identifier. if (TD->isExternallyVisible()) return true; + // CodeView types with C++ mangling need a type identifier. + if (CGM.getCodeGenOpts().EmitCodeView) + return true; + return false; } -// When emitting CodeView debug information we need to produce a type -// identifier for all types which have a C++ mangling. Until a GUID is added -// to the identifier (not currently implemented) the result will not be unique -// across compilation units. -// When emitting DWARF debug information, we need to produce a type identifier -// for all externally visible types with C++ name mangling. This identifier -// should be unique across ODR-compliant compilation units. +// Returns a unique type identifier string if one exists, or an empty string. static SmallString<256> getTypeIdentifier(const TagType *Ty, CodeGenModule &CGM, llvm::DICompileUnit *TheCU) { SmallString<256> Identifier; |
