https://github.com/rnk updated https://github.com/llvm/llvm-project/pull/107154
>From cfb2cea5a4d4e0c1712e038692c4c5acee6b1f27 Mon Sep 17 00:00:00 2001
From: Reid Kleckner <r...@google.com>
Date: Tue, 3 Sep 2024 21:16:40 +0000
Subject: [PATCH 1/2] [MS] Put dllexported inline global initializers in a
comdat
Follow-up to c19f4f8069722f6804086d4438a0254104242c46 to handle corner
case of exported inline variables.
Should fix #56485
---
clang/lib/CodeGen/CGDeclCXX.cpp | 2 +-
clang/test/CodeGenCXX/microsoft-abi-template-static-init.cpp | 5 ++---
2 files changed, 3 insertions(+), 4 deletions(-)
diff --git a/clang/lib/CodeGen/CGDeclCXX.cpp b/clang/lib/CodeGen/CGDeclCXX.cpp
index 2f56355cff90ec..c9e0fb0d8afaba 100644
--- a/clang/lib/CodeGen/CGDeclCXX.cpp
+++ b/clang/lib/CodeGen/CGDeclCXX.cpp
@@ -586,7 +586,7 @@ CodeGenModule::EmitCXXGlobalVarDeclInitFunc(const VarDecl
*D,
PrioritizedCXXGlobalInits.size());
PrioritizedCXXGlobalInits.push_back(std::make_pair(Key, Fn));
} else if (isTemplateInstantiation(D->getTemplateSpecializationKind()) ||
- getContext().GetGVALinkageForVariable(D) == GVA_DiscardableODR ||
+ !isUniqueGVALinkage(getContext().GetGVALinkageForVariable(D)) ||
D->hasAttr<SelectAnyAttr>()) {
// C++ [basic.start.init]p2:
// Definitions of explicitly specialized class template static data
diff --git a/clang/test/CodeGenCXX/microsoft-abi-template-static-init.cpp
b/clang/test/CodeGenCXX/microsoft-abi-template-static-init.cpp
index 60b48abca2f89a..871551240debfd 100644
--- a/clang/test/CodeGenCXX/microsoft-abi-template-static-init.cpp
+++ b/clang/test/CodeGenCXX/microsoft-abi-template-static-init.cpp
@@ -49,8 +49,6 @@ struct X {
static T ioo;
static T init();
};
-// template specialized static data don't need in llvm.used,
-// the static init routine get call from _GLOBAL__sub_I_ routines.
template <> int X<int>::ioo = X<int>::init();
template struct X<int>;
class a {
@@ -87,5 +85,6 @@ struct S1
int foo();
inline int zoo = foo();
inline static int boo = foo();
+inline __declspec(dllexport) A exported_inline{};
-// CHECK: @llvm.used = appending global [8 x ptr] [ptr
@"?x@selectany_init@@3HA", ptr @"?x1@selectany_init@@3HA", ptr
@"?x@?$A@H@explicit_template_instantiation@@2HA", ptr @"?ioo@?$X_@H@@2HA", ptr
@"?aoo@S1@@2UA@@A", ptr @"?zoo@@3HA", ptr @"?s@?$ExportedTemplate@H@@2US@@A",
ptr @"?x@?$A@H@implicit_template_instantiation@@2HA"], section "llvm.metadata"
+// CHECK: @llvm.used = appending global [10 x ptr] [ptr
@"?x@selectany_init@@3HA", ptr @"?x1@selectany_init@@3HA", ptr
@"?x@?$A@H@explicit_template_instantiation@@2HA", ptr @"?ioo@?$X_@H@@2HA", ptr
@"?ioo@?$X@H@@2HA", ptr @"?aoo@S1@@2UA@@A", ptr @"?zoo@@3HA", ptr
@"?exported_inline@@3UA@@A", ptr @"?s@?$ExportedTemplate@H@@2US@@A", ptr
@"?x@?$A@H@implicit_template_instantiation@@2HA"], section "llvm.metadata"
>From 3cb368a8c01f99a7b12ece55e5b2145650d4f89d Mon Sep 17 00:00:00 2001
From: Reid Kleckner <r...@google.com>
Date: Tue, 3 Sep 2024 23:38:51 +0000
Subject: [PATCH 2/2] Update comment block on why vague linkage global
initialization is different
---
clang/lib/CodeGen/CGDeclCXX.cpp | 41 ++++++++++++++++++++++++---------
1 file changed, 30 insertions(+), 11 deletions(-)
diff --git a/clang/lib/CodeGen/CGDeclCXX.cpp b/clang/lib/CodeGen/CGDeclCXX.cpp
index c9e0fb0d8afaba..1ae8a2674df20d 100644
--- a/clang/lib/CodeGen/CGDeclCXX.cpp
+++ b/clang/lib/CodeGen/CGDeclCXX.cpp
@@ -588,29 +588,48 @@ CodeGenModule::EmitCXXGlobalVarDeclInitFunc(const VarDecl
*D,
} else if (isTemplateInstantiation(D->getTemplateSpecializationKind()) ||
!isUniqueGVALinkage(getContext().GetGVALinkageForVariable(D)) ||
D->hasAttr<SelectAnyAttr>()) {
+ // For vague linkage globals, put the initializer into its own global_ctors
+ // entry with the global as a comdat key. This ensures at most one
+ // initializer per DSO runs during DSO dynamic initialization.
+ //
+ // For ELF platforms, this is an important code size and startup time
+ // optimization. For dynamic, non-hidden symbols, the weak guard variable
+ // remains to ensure that other DSOs do not re-initialize the global.
+ //
+ // For PE-COFF platforms, there is no guard variable, and COMDAT
associativity
+ // is the only way to ensure vauge linkage globals are initialized exactly
+ // once.
+ //
+ // MachO is the only remaining platform with no comdats that doesn't
+ // benefit from this optimization. The rest are mainly modeled on ELF
+ // behavior.
+ //
+ // C++ requires that inline global variables are initialized in source
+ // order, but this requirement does not exist for templated entities.
+ // llvm.global_ctors does not guarantee initialization order, so in
+ // general, Clang does not fully conform to the ordering requirement.
+ // However, in practice, LLVM emits global_ctors in the provided order, and
+ // users typically don't rely on ordering between inline globals in
+ // different headers which are then transitively included in varying order.
+ // Clang's current behavior is a practical tradeoff, since dropping the
+ // comdat would lead to unacceptable impact on code size and startup time.
+ //
+ // FIXME: Find a solution to guarantee source-order initialization of
+ // inline variables.
+ //
// C++ [basic.start.init]p2:
// Definitions of explicitly specialized class template static data
// members have ordered initialization. Other class template static data
// members (i.e., implicitly or explicitly instantiated specializations)
// have unordered initialization.
//
- // As a consequence, we can put them into their own llvm.global_ctors
entry.
- //
- // If the global is externally visible, put the initializer into a COMDAT
- // group with the global being initialized. On most platforms, this is a
- // minor startup time optimization. In the MS C++ ABI, there are no guard
- // variables, so this COMDAT key is required for correctness.
- //
- // SelectAny globals will be comdat-folded. Put the initializer into a
- // COMDAT group associated with the global, so the initializers get folded
- // too.
- I = DelayedCXXInitPosition.find(D);
// CXXGlobalInits.size() is the lex order number for the next deferred
// VarDecl. Use it when the current VarDecl is non-deferred. Although this
// lex order number is shared between current VarDecl and some following
// VarDecls, their order of insertion into `llvm.global_ctors` is the same
// as the lexing order and the following stable sort would preserve such
// order.
+ I = DelayedCXXInitPosition.find(D);
unsigned LexOrder =
I == DelayedCXXInitPosition.end() ? CXXGlobalInits.size() : I->second;
AddGlobalCtor(Fn, 65535, LexOrder, COMDATKey);
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