[CodeGen] Disable aggressive structor optimizations at -O0, take 2
The first version of the patch (r332228) was flawed because it was
putting structors into C5/D5 comdats very eagerly. This is correct only
if we can ensure the comdat contains all required versions of the
structor (which wasn't the case). This version uses a more nuanced
approach:
- for local structor symbols we use an alias because we don't have to
worry about comdats or other compilation units.
- linkonce symbols are emitted separately, as we cannot guarantee we
will have all symbols we need to form a comdat (they are emitted
lazily, only when referenced).
- available_externally symbols are also emitted separately, as the code
seemed to be worried about emitting an alias in this case.
- other linkage types are not affected by the optimization level. They
either get put into a comdat (weak) or get aliased (external).
Reviewers: rjmccall, aprantl
Subscribers: cfe-commits
Differential Revision: https://reviews.llvm.org/D46685
llvm-svn: 332839
diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp b/clang/lib/CodeGen/ItaniumCXXABI.cpp
index c77644b..0374e4c 100644
--- a/clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -3628,12 +3628,22 @@
}
llvm::GlobalValue::LinkageTypes Linkage = CGM.getFunctionLinkage(AliasDecl);
- if (llvm::GlobalValue::isDiscardableIfUnused(Linkage))
- return StructorCodegen::RAUW;
+ // All discardable structors can be RAUWed, but we don't want to do that in
+ // unoptimized code, as that makes complete structor symbol disappear
+ // completely, which degrades debugging experience.
+ // Symbols with private linkage can be safely aliased, so we special case them
+ // here.
+ if (llvm::GlobalValue::isLocalLinkage(Linkage))
+ return CGM.getCodeGenOpts().OptimizationLevel > 0 ? StructorCodegen::RAUW
+ : StructorCodegen::Alias;
+ // Linkonce structors cannot be aliased nor placed in a comdat, so these need
+ // to be emitted separately.
// FIXME: Should we allow available_externally aliases?
- if (!llvm::GlobalAlias::isValidLinkage(Linkage))
- return StructorCodegen::RAUW;
+ if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) ||
+ !llvm::GlobalAlias::isValidLinkage(Linkage))
+ return CGM.getCodeGenOpts().OptimizationLevel > 0 ? StructorCodegen::RAUW
+ : StructorCodegen::Emit;
if (llvm::GlobalValue::isWeakForLinker(Linkage)) {
// Only ELF and wasm support COMDATs with arbitrary names (C5/D5).