plotfi created this revision.
plotfi added reviewers: rjmccall, manmanren, MadCoder.
Herald added subscribers: cfe-commits, dang.
Herald added a project: clang.
plotfi requested review of this revision.
Hi @rjmccall @MadCoder
I'd like to preface this diff: I mostly want to discuss the prospects of
exporting generated wrappers that call objc_direct methods, or alternately
exporting the objc_direct methods themselves when an optional CodeGenOpts
command-line flag is specified. This diff implements generating wrappers when a
CodeGenOpts command-line flag is provided since C wrappers were mentioned in
the original objc_direct diff. However I do think it might be possible to
export the methods directly provided the implicit '_' underbar prefix is
prepended to satisfy C naming on Darwin, and if thats the case I can post a
diff that does that instead. Anyways, thats all I wanted to preface with.
Thanks.
Motivated by the potential benefit of using the objc_direct attribute, this
diff aims to expand support to cross dylib objc_direct method calls by
automatically generating exportable wrapper functions that call objc_direct
methods internal to a dylib.
In the original patch landed in https://reviews.llvm.org/D69991 it mentions:
"The symbol for the method has enforced hidden visibility and such direct
calls are hence unreachable cross image. An explicit C function must be
made if so desired to wrap them."
This change provides a codegen options flag to clang
`-fobjc-export-direct-method-wrappers` to generate the wrapper functions that
begin with the prefix __objc_direct_wrapper and are marked as
__attribute__((alwaysinline)). This way within a link unit the wrapper
functions should be inlined away at their call sites, but across a dylib
boundary the wrapper call is used.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D86049
Files:
clang/include/clang/Basic/CodeGenOptions.def
clang/include/clang/Driver/Options.td
clang/lib/CodeGen/CGObjC.cpp
clang/lib/CodeGen/CGObjCMac.cpp
clang/lib/Driver/ToolChains/Clang.cpp
clang/lib/Frontend/CompilerInvocation.cpp
Index: clang/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- clang/lib/Frontend/CompilerInvocation.cpp
+++ clang/lib/Frontend/CompilerInvocation.cpp
@@ -1283,6 +1283,8 @@
}
}
+ if (Args.hasArg(OPT_fobjc_export_direct_method_wrappers))
+ Opts.ObjCExportDirectMethodWrappers = 1;
if (Args.hasArg(OPT_fno_objc_convert_messages_to_runtime_calls))
Opts.ObjCConvertMessagesToRuntimeCalls = 0;
Index: clang/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -3462,6 +3462,9 @@
CmdArgs.push_back("-fno-objc-convert-messages-to-runtime-calls");
}
+ if (Args.hasArg(options::OPT_fobjc_export_direct_method_wrappers))
+ CmdArgs.push_back("-fobjc-export-direct-method-wrappers");
+
// -fobjc-infer-related-result-type is the default, except in the Objective-C
// rewriter.
if (InferCovariantReturns)
Index: clang/lib/CodeGen/CGObjCMac.cpp
===================================================================
--- clang/lib/CodeGen/CGObjCMac.cpp
+++ clang/lib/CodeGen/CGObjCMac.cpp
@@ -2143,6 +2143,36 @@
return false;
}
+/// Create or look up the declaration of an objc_direct method wrapper.
+llvm::Function *getObjCDirectWrapper(llvm::Function &F) {
+ std::string NewName = "__objc_direct_wrapper";
+ for (auto C : F.getName().str()) {
+ if (C == '\1')
+ continue;
+ NewName += C;
+ }
+
+ auto WI = llvm::find_if(*F.getParent(), [NewName](const llvm::Function &F) {
+ return F.getName() == NewName;
+ });
+
+ llvm::Function *Wrapper = nullptr;
+ if (WI == F.getParent()->end()) {
+ llvm::Module &M = *F.getParent();
+ llvm::FunctionType *FnTy = F.getFunctionType();
+ Wrapper = llvm::Function::Create(FnTy, F.getLinkage(), F.getAddressSpace(),
+ NewName);
+ Wrapper->setLinkage(llvm::GlobalValue::ExternalLinkage);
+ Wrapper->addFnAttr(llvm::Attribute::AlwaysInline);
+ Wrapper->setVisibility(llvm::Function::DefaultVisibility);
+ M.getFunctionList().insert(F.getIterator(), Wrapper);
+ } else {
+ Wrapper = &*WI;
+ }
+
+ return Wrapper;
+}
+
CodeGen::RValue
CGObjCCommonMac::EmitMessageSend(CodeGen::CodeGenFunction &CGF,
ReturnValueSlot Return,
@@ -2214,7 +2244,13 @@
llvm::FunctionCallee Fn = nullptr;
if (Method && Method->isDirectMethod()) {
- Fn = GenerateDirectMethod(Method, Method->getClassInterface());
+ if (CGM.getCodeGenOpts().ObjCExportDirectMethodWrappers) {
+ llvm::Function *FnDirect =
+ GenerateDirectMethod(Method, Method->getClassInterface());
+ Fn = getObjCDirectWrapper(*FnDirect);
+ } else {
+ Fn = GenerateDirectMethod(Method, Method->getClassInterface());
+ }
} else if (CGM.ReturnSlotInterferesWithArgs(MSI.CallInfo)) {
if (ReceiverCanBeNull) RequiresNullCheck = true;
Fn = (ObjCABI == 2) ? ObjCTypes.getSendStretFn2(IsSuper)
@@ -4006,6 +4042,9 @@
if (OMD->isDirectMethod()) {
Method = GenerateDirectMethod(OMD, CD);
+ if (CGM.getCodeGenOpts().ObjCExportDirectMethodWrappers) {
+ getObjCDirectWrapper(*Method);
+ }
} else {
SmallString<256> Name;
GetNameForMethod(OMD, CD, Name);
Index: clang/lib/CodeGen/CGObjC.cpp
===================================================================
--- clang/lib/CodeGen/CGObjC.cpp
+++ clang/lib/CodeGen/CGObjC.cpp
@@ -673,6 +673,33 @@
};
}
+/// Populates the body of a objc_direct wrapper function.
+/// This should be done in the same TU that we are populating the definition of
+/// the objc_direct method it is wrapping.
+static void populateObjCDirectWrapperContent(llvm::Function &Wrapper,
+ llvm::Function &F) {
+ assert(Wrapper.isDeclaration() &&
+ "Expected empty objc_direct wrapper function.");
+ llvm::Module &M = *F.getParent();
+ llvm::LLVMContext &Ctx = M.getContext();
+ llvm::BasicBlock *EntryBB = llvm::BasicBlock::Create(Ctx, "entry", &Wrapper);
+
+ llvm::SmallVector<llvm::Value *, 8> Args;
+ auto FArgIt = F.arg_begin();
+ for (llvm::Argument &Arg : Wrapper.args()) {
+ Args.push_back(&Arg);
+ Arg.setName((FArgIt++)->getName());
+ }
+
+ llvm::CallInst *CI = llvm::CallInst::Create(&F, Args, "", EntryBB);
+ CI->setTailCall(true);
+ CI->addAttribute(llvm::AttributeList::FunctionIndex,
+ llvm::Attribute::NoInline);
+ llvm::ReturnInst::Create(Ctx, CI->getType()->isVoidTy() ? nullptr : CI,
+ EntryBB);
+}
+llvm::Function *getObjCDirectWrapper(llvm::Function &F);
+
/// StartObjCMethod - Begin emission of an ObjCMethod. This generates
/// the LLVM function and sets the other context used by
/// CodeGenFunction.
@@ -712,6 +739,10 @@
//
// TODO: possibly have several entry points to elide the check
CGM.getObjCRuntime().GenerateDirectMethodPrologue(*this, Fn, OMD, CD);
+ if (CGM.getCodeGenOpts().ObjCExportDirectMethodWrappers) {
+ llvm::Function *Wrapper = getObjCDirectWrapper(*Fn);
+ populateObjCDirectWrapperContent(*Wrapper, *Fn);
+ }
}
// In ARC, certain methods get an extra cleanup.
Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -1622,6 +1622,8 @@
Flag<["-"], "fobjc-convert-messages-to-runtime-calls">, Group<f_Group>;
def fno_objc_convert_messages_to_runtime_calls :
Flag<["-"], "fno-objc-convert-messages-to-runtime-calls">, Group<f_Group>, Flags<[CC1Option]>;
+def fobjc_export_direct_method_wrappers :
+ Flag<["-"], "fobjc-export-direct-method-wrappers">, Group<f_Group>, Flags<[CC1Option]>;
def fobjc_arc_exceptions : Flag<["-"], "fobjc-arc-exceptions">, Group<f_Group>, Flags<[CC1Option]>,
HelpText<"Use EH-safe code when synthesizing retains and releases in -fobjc-arc">;
def fno_objc_arc_exceptions : Flag<["-"], "fno-objc-arc-exceptions">, Group<f_Group>;
Index: clang/include/clang/Basic/CodeGenOptions.def
===================================================================
--- clang/include/clang/Basic/CodeGenOptions.def
+++ clang/include/clang/Basic/CodeGenOptions.def
@@ -173,6 +173,8 @@
ENUM_CODEGENOPT(ObjCDispatchMethod, ObjCDispatchMethodKind, 2, Legacy)
/// Replace certain message sends with calls to ObjC runtime entrypoints
CODEGENOPT(ObjCConvertMessagesToRuntimeCalls , 1, 1)
+/// Generate and export wrapper functions for objc_direct methods.
+CODEGENOPT(ObjCExportDirectMethodWrappers , 1, 0)
VALUE_CODEGENOPT(OptimizationLevel, 2, 0) ///< The -O[0-3] option specified.
VALUE_CODEGENOPT(OptimizeSize, 2, 0) ///< If -Os (==1) or -Oz (==2) is specified.
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