aeubanks updated this revision to Diff 552889.
aeubanks edited the summary of this revision.
aeubanks added a comment.
add warning
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D158223/new/
https://reviews.llvm.org/D158223
Files:
clang/include/clang/Basic/Attr.td
clang/include/clang/Basic/AttrDocs.td
clang/include/clang/Basic/DiagnosticSemaKinds.td
clang/lib/CodeGen/CodeGenModule.cpp
clang/lib/Sema/SemaDecl.cpp
clang/test/CodeGen/unnamed-addr.c
clang/test/SemaCXX/unnamed-addr.cpp
Index: clang/test/SemaCXX/unnamed-addr.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/unnamed-addr.cpp
@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+struct Foo {
+ int a;
+};
+
+struct Bar {
+ int a;
+ Bar();
+};
+
+[[clang::unnamed_addr]] const int i = 8;
+
+[[clang::unnamed_addr]] int i2 = 8; // expected-warning{{unnamed_addr should only be used on const POD (plain old data) globals}}
+
+[[clang::unnamed_addr]] const Foo j = {2};
+
+[[clang::unnamed_addr]] Foo j2 = {2}; // expected-warning{{unnamed_addr should only be used on const POD (plain old data) globals}}
+
+[[clang::unnamed_addr]] const Bar k; // expected-warning{{unnamed_addr should only be used on const POD (plain old data) globals}}
Index: clang/test/CodeGen/unnamed-addr.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/unnamed-addr.c
@@ -0,0 +1,5 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -O1 -emit-llvm -o - -disable-llvm-passes %s | FileCheck %s
+
+// CHECK: @i = unnamed_addr constant i32 8
+
+[[clang::unnamed_addr]] const int i = 8;
Index: clang/lib/Sema/SemaDecl.cpp
===================================================================
--- clang/lib/Sema/SemaDecl.cpp
+++ clang/lib/Sema/SemaDecl.cpp
@@ -14519,6 +14519,13 @@
PragmaClangRelroSection.PragmaLocation));
}
+ if (VD->hasGlobalStorage() && VD->isThisDeclarationADefinition() &&
+ VD->hasAttr<UnnamedAddrAttr>() &&
+ (!VD->getType().isPODType(getASTContext()) ||
+ !VD->getType().isConstQualified())) {
+ Diag(VD->getLocation(), diag::warn_attribute_unnamed_addr);
+ }
+
if (auto *DD = dyn_cast<DecompositionDecl>(ThisDecl)) {
for (auto *BD : DD->bindings()) {
FinalizeDeclaration(BD);
Index: clang/lib/CodeGen/CodeGenModule.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenModule.cpp
+++ clang/lib/CodeGen/CodeGenModule.cpp
@@ -5255,6 +5255,9 @@
GV->setConstant(true);
}
+ if (D->hasAttr<UnnamedAddrAttr>())
+ GV->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
+
CharUnits AlignVal = getContext().getDeclAlign(D);
// Check for alignment specifed in an 'omp allocate' directive.
if (std::optional<CharUnits> AlignValFromAllocate =
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -3587,6 +3587,9 @@
"weakref declaration of %0 must be in a global context">;
def err_attribute_weakref_without_alias : Error<
"weakref declaration of %0 must also have an alias attribute">;
+def warn_attribute_unnamed_addr : Warning<
+ "unnamed_addr should only be used on const POD (plain old data) globals">,
+ InGroup<DiagGroup<"unnamed-addr">>;
def err_alias_not_supported_on_darwin : Error <
"aliases are not supported on darwin">;
def warn_attribute_wrong_decl_type_str : Warning<
Index: clang/include/clang/Basic/AttrDocs.td
===================================================================
--- clang/include/clang/Basic/AttrDocs.td
+++ clang/include/clang/Basic/AttrDocs.td
@@ -1408,6 +1408,24 @@
}];
}
+def UnnamedAddrDocs : Documentation {
+ let Category = DocCatField;
+ let Content = [{
+The ``clang::unnamed_addr`` attribute specifies that the address of a global is
+not significant. This allows global constants with the same contents to be
+merged. This can break global pointer identity, i.e. two different globals have
+the same address.
+
+Example usage:
+
+.. code-block:: c
+
+ // i and j may have the same address.
+ [[clang::unnamed_addr]] const int i = 42;
+ [[clang::unnamed_addr]] const int j = 42;
+ }];
+}
+
def ObjCRequiresSuperDocs : Documentation {
let Category = DocCatFunction;
let Content = [{
Index: clang/include/clang/Basic/Attr.td
===================================================================
--- clang/include/clang/Basic/Attr.td
+++ clang/include/clang/Basic/Attr.td
@@ -1794,6 +1794,13 @@
let SimpleHandler = 1;
}
+def UnnamedAddr : InheritableAttr {
+ let Spellings = [Clang<"unnamed_addr">];
+ let Subjects = SubjectList<[GlobalVar], ErrorDiag>;
+ let Documentation = [UnnamedAddrDocs];
+ let SimpleHandler = 1;
+}
+
def ReturnsTwice : InheritableAttr {
let Spellings = [GCC<"returns_twice">];
let Subjects = SubjectList<[Function]>;
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