[PATCH] D30977: [CodeGen] Emit a CoreFoundation link guard when @available is used

2017-03-23 Thread Alex Lorenz via Phabricator via cfe-commits 
This revision was automatically updated to reflect the committed changes.
Closed by commit rL298588: [CodeGen] Emit a CoreFoundation link guard when 
@available is used (authored by arphaman).

Changed prior to commit:
  https://reviews.llvm.org/D30977?vs=92028=92780#toc

Repository:
  rL LLVM

https://reviews.llvm.org/D30977

Files:
  cfe/trunk/lib/CodeGen/CGObjC.cpp
  cfe/trunk/lib/CodeGen/CodeGenModule.cpp
  cfe/trunk/lib/CodeGen/CodeGenModule.h
  cfe/trunk/test/CodeGenObjC/availability-cf-link-guard.m

Index: cfe/trunk/test/CodeGenObjC/availability-cf-link-guard.m
===
--- cfe/trunk/test/CodeGenObjC/availability-cf-link-guard.m
+++ cfe/trunk/test/CodeGenObjC/availability-cf-link-guard.m
@@ -0,0 +1,45 @@
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.11 -emit-llvm -o - %s | FileCheck --check-prefixes=CHECK,CHECK_LINK_OPT %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.11 -emit-llvm -o - -D USE_BUILTIN %s | FileCheck --check-prefixes=CHECK,CHECK_LINK_OPT %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.11 -emit-llvm -o - -D DEF_CF %s | FileCheck --check-prefixes=CHECK_CF,CHECK_LINK_OPT %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.12 -emit-llvm -o - %s | FileCheck --check-prefix=CHECK_NO_GUARD %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux -emit-llvm -o - %s | FileCheck --check-prefix=CHECK_NO_GUARD %s
+
+#ifdef DEF_CF
+struct CFBundle;
+typedef struct CFBundle *CFBundleRef;
+unsigned CFBundleGetVersionNumber(CFBundleRef bundle);
+// CHECK_CF: declare i32 @CFBundleGetVersionNumber(%struct.CFBundle*)
+// CHECK_CF: @__clang_at_available_requires_core_foundation_framework
+// CHECK_CF-NEXT: call {{.*}}@CFBundleGetVersionNumber
+#endif
+
+void use_at_available() {
+#ifdef DEF_CF
+  CFBundleGetVersionNumber(0);
+#endif
+#ifdef USE_BUILTIN
+  if (__builtin_available(macos 10.12, *))
+;
+#else
+  if (@available(macos 10.12, *))
+;
+#endif
+}
+
+// CHECK: @llvm.compiler.used{{.*}}@__clang_at_available_requires_core_foundation_framework
+
+// CHECK: declare i32 @CFBundleGetVersionNumber(i8*)
+
+// CHECK-LABEL: linkonce hidden void @__clang_at_available_requires_core_foundation_framework
+// CHECK: call i32 @CFBundleGetVersionNumber(i8* null)
+// CHECK-NEXT: unreachable
+
+// CHECK_NO_GUARD-NOT: __clang_at_available_requires_core_foundation_framework
+// CHECK_NO_GUARD-NOT: CFBundleGetVersionNumber
+
+// CHECK_LINK_OPT: !"Linker Options", ![[OPTS:[0-9]+]]
+// CHECK_LINK_OPT: ![[OPTS]] = !{![[FRAMEWORK:[0-9]+]]
+// CHECK_LINK_OPT: ![[FRAMEWORK]] = !{!"-framework", !"CoreFoundation"}
+
+// CHECK_NO_GUARD-NOT: "Linker Options"
+// CHECK_NO_GUARD-NOT: CoreFoundation
Index: cfe/trunk/lib/CodeGen/CodeGenModule.cpp
===
--- cfe/trunk/lib/CodeGen/CodeGenModule.cpp
+++ cfe/trunk/lib/CodeGen/CodeGenModule.cpp
@@ -414,6 +414,7 @@
 CoverageMapping->emit();
   if (CodeGenOpts.SanitizeCfiCrossDso)
 CodeGenFunction(*this).EmitCfiCheckFail();
+  emitAtAvailableLinkGuard();
   emitLLVMUsed();
   if (SanStats)
 SanStats->finish();
Index: cfe/trunk/lib/CodeGen/CodeGenModule.h
===
--- cfe/trunk/lib/CodeGen/CodeGenModule.h
+++ cfe/trunk/lib/CodeGen/CodeGenModule.h
@@ -1286,6 +1286,10 @@
   /// Emit any vtables which we deferred and still have a use for.
   void EmitDeferredVTables();
 
+  /// Emit a dummy function that reference a CoreFoundation symbol when
+  /// @available is used on Darwin.
+  void emitAtAvailableLinkGuard();
+
   /// Emit the llvm.used and llvm.compiler.used metadata.
   void emitLLVMUsed();
 
Index: cfe/trunk/lib/CodeGen/CGObjC.cpp
===
--- cfe/trunk/lib/CodeGen/CGObjC.cpp
+++ cfe/trunk/lib/CodeGen/CGObjC.cpp
@@ -3416,4 +3416,37 @@
   return Builder.CreateICmpNE(CallRes, llvm::Constant::getNullValue(Int32Ty));
 }
 
+void CodeGenModule::emitAtAvailableLinkGuard() {
+  if (!IsOSVersionAtLeastFn)
+return;
+  // @available requires CoreFoundation only on Darwin.
+  if (!Target.getTriple().isOSDarwin())
+return;
+  // Add -framework CoreFoundation to the linker commands. We still want to
+  // emit the core foundation reference down below because otherwise if
+  // CoreFoundation is not used in the code, the linker won't link the
+  // framework.
+  auto  = getLLVMContext();
+  llvm::Metadata *Args[2] = {llvm::MDString::get(Context, "-framework"),
+ llvm::MDString::get(Context, "CoreFoundation")};
+  LinkerOptionsMetadata.push_back(llvm::MDNode::get(Context, Args));
+  // Emit a reference to a symbol from CoreFoundation to ensure that
+  // CoreFoundation is linked into the final binary.
+  llvm::FunctionType *FTy =
+  llvm::FunctionType::get(Int32Ty, {VoidPtrTy}, false);
+  llvm::Constant *CFFunc =
+  CreateRuntimeFunction(FTy, "CFBundleGetVersionNumber");
+
+  llvm::FunctionType

[PATCH] D30977: [CodeGen] Emit a CoreFoundation link guard when @available is used

2017-03-17 Thread John McCall via Phabricator via cfe-commits 
rjmccall accepted this revision.
rjmccall added a comment.
This revision is now accepted and ready to land.

LGTM.




Comment at: lib/CodeGen/CGObjC.cpp:3428
+  // CoreFoundation is not used in the code, the linker won't link the
+  // framework.
+  auto  = getLLVMContext();

arphaman wrote:
> rjmccall wrote:
> > Can you explain why compiler-rt has to load the symbol at runtime?  Is this 
> > just some compiler-rt testing thing?  Because it seems like a shame to pay 
> > a code-size cost — even a negligible one — for something like that.
> Because compiler-rt is linked into some internal projects that use the 
> `-all_load` flag, so the linker loads `__isOSVersionAtLeast` that references 
> the CoreFoundation symbols even when it's not used in code.
Well, that is terrible.


Repository:
  rL LLVM

https://reviews.llvm.org/D30977



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[PATCH] D30977: [CodeGen] Emit a CoreFoundation link guard when @available is used

2017-03-16 Thread Alex Lorenz via Phabricator via cfe-commits 
arphaman updated this revision to Diff 92028.
arphaman marked an inline comment as done.
arphaman added a comment.

Reverse the early exit checks.


Repository:
  rL LLVM

https://reviews.llvm.org/D30977

Files:
  lib/CodeGen/CGObjC.cpp
  lib/CodeGen/CodeGenModule.cpp
  lib/CodeGen/CodeGenModule.h
  test/CodeGenObjC/availability-cf-link-guard.m

Index: test/CodeGenObjC/availability-cf-link-guard.m
===
--- /dev/null
+++ test/CodeGenObjC/availability-cf-link-guard.m
@@ -0,0 +1,45 @@
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.11 -emit-llvm -o - %s | FileCheck --check-prefixes=CHECK,CHECK_LINK_OPT %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.11 -emit-llvm -o - -D USE_BUILTIN %s | FileCheck --check-prefixes=CHECK,CHECK_LINK_OPT %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.11 -emit-llvm -o - -D DEF_CF %s | FileCheck --check-prefixes=CHECK_CF,CHECK_LINK_OPT %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.12 -emit-llvm -o - %s | FileCheck --check-prefix=CHECK_NO_GUARD %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux -emit-llvm -o - %s | FileCheck --check-prefix=CHECK_NO_GUARD %s
+
+#ifdef DEF_CF
+struct CFBundle;
+typedef struct CFBundle *CFBundleRef;
+unsigned CFBundleGetVersionNumber(CFBundleRef bundle);
+// CHECK_CF: declare i32 @CFBundleGetVersionNumber(%struct.CFBundle*)
+// CHECK_CF: @__clang_at_available_requires_core_foundation_framework
+// CHECK_CF-NEXT: call {{.*}}@CFBundleGetVersionNumber
+#endif
+
+void use_at_available() {
+#ifdef DEF_CF
+  CFBundleGetVersionNumber(0);
+#endif
+#ifdef USE_BUILTIN
+  if (__builtin_available(macos 10.12, *))
+;
+#else
+  if (@available(macos 10.12, *))
+;
+#endif
+}
+
+// CHECK: @llvm.compiler.used{{.*}}@__clang_at_available_requires_core_foundation_framework
+
+// CHECK: declare i32 @CFBundleGetVersionNumber(i8*)
+
+// CHECK-LABEL: linkonce hidden void @__clang_at_available_requires_core_foundation_framework
+// CHECK: call i32 @CFBundleGetVersionNumber(i8* null)
+// CHECK-NEXT: unreachable
+
+// CHECK_NO_GUARD-NOT: __clang_at_available_requires_core_foundation_framework
+// CHECK_NO_GUARD-NOT: CFBundleGetVersionNumber
+
+// CHECK_LINK_OPT: !"Linker Options", ![[OPTS:[0-9]+]]
+// CHECK_LINK_OPT: ![[OPTS]] = !{![[FRAMEWORK:[0-9]+]]
+// CHECK_LINK_OPT: ![[FRAMEWORK]] = !{!"-framework", !"CoreFoundation"}
+
+// CHECK_NO_GUARD-NOT: "Linker Options"
+// CHECK_NO_GUARD-NOT: CoreFoundation
Index: lib/CodeGen/CodeGenModule.h
===
--- lib/CodeGen/CodeGenModule.h
+++ lib/CodeGen/CodeGenModule.h
@@ -1288,6 +1288,10 @@
   /// Emit any vtables which we deferred and still have a use for.
   void EmitDeferredVTables();
 
+  /// Emit a dummy function that reference a CoreFoundation symbol when
+  /// @available is used on Darwin.
+  void emitAtAvailableLinkGuard();
+
   /// Emit the llvm.used and llvm.compiler.used metadata.
   void emitLLVMUsed();
 
Index: lib/CodeGen/CodeGenModule.cpp
===
--- lib/CodeGen/CodeGenModule.cpp
+++ lib/CodeGen/CodeGenModule.cpp
@@ -408,6 +408,7 @@
 CoverageMapping->emit();
   if (CodeGenOpts.SanitizeCfiCrossDso)
 CodeGenFunction(*this).EmitCfiCheckFail();
+  emitAtAvailableLinkGuard();
   emitLLVMUsed();
   if (SanStats)
 SanStats->finish();
Index: lib/CodeGen/CGObjC.cpp
===
--- lib/CodeGen/CGObjC.cpp
+++ lib/CodeGen/CGObjC.cpp
@@ -3416,4 +3416,37 @@
   return Builder.CreateICmpNE(CallRes, llvm::Constant::getNullValue(Int32Ty));
 }
 
+void CodeGenModule::emitAtAvailableLinkGuard() {
+  if (!IsOSVersionAtLeastFn)
+return;
+  // @available requires CoreFoundation only on Darwin.
+  if (!Target.getTriple().isOSDarwin())
+return;
+  // Add -framework CoreFoundation to the linker commands. We still want to
+  // emit the core foundation reference down below because otherwise if
+  // CoreFoundation is not used in the code, the linker won't link the
+  // framework.
+  auto  = getLLVMContext();
+  llvm::Metadata *Args[2] = {llvm::MDString::get(Context, "-framework"),
+ llvm::MDString::get(Context, "CoreFoundation")};
+  LinkerOptionsMetadata.push_back(llvm::MDNode::get(Context, Args));
+  // Emit a reference to a symbol from CoreFoundation to ensure that
+  // CoreFoundation is linked into the final binary.
+  llvm::FunctionType *FTy =
+  llvm::FunctionType::get(Int32Ty, {VoidPtrTy}, false);
+  llvm::Constant *CFFunc =
+  CreateRuntimeFunction(FTy, "CFBundleGetVersionNumber");
+
+  llvm::FunctionType *CheckFTy = llvm::FunctionType::get(VoidTy, {}, false);
+  llvm::Function *CFLinkCheckFunc = cast(CreateBuiltinFunction(
+  CheckFTy, "__clang_at_available_requires_core_foundation_framework"));
+  CFLinkCheckFunc->setLinkage(llvm::GlobalValue::LinkOnceAnyLinkage);
+

[PATCH] D30977: [CodeGen] Emit a CoreFoundation link guard when @available is used

2017-03-16 Thread Alex Lorenz via Phabricator via cfe-commits 
arphaman added inline comments.



Comment at: lib/CodeGen/CGObjC.cpp:3428
+  // CoreFoundation is not used in the code, the linker won't link the
+  // framework.
+  auto  = getLLVMContext();

rjmccall wrote:
> Can you explain why compiler-rt has to load the symbol at runtime?  Is this 
> just some compiler-rt testing thing?  Because it seems like a shame to pay a 
> code-size cost — even a negligible one — for something like that.
Because compiler-rt is linked into some internal projects that use the 
`-all_load` flag, so the linker loads `__isOSVersionAtLeast` that references 
the CoreFoundation symbols even when it's not used in code.


Repository:
  rL LLVM

https://reviews.llvm.org/D30977



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[PATCH] D30977: [CodeGen] Emit a CoreFoundation link guard when @available is used

2017-03-16 Thread John McCall via Phabricator via cfe-commits 
rjmccall added inline comments.



Comment at: lib/CodeGen/CGObjC.cpp:3423
+return;
+  if (!IsOSVersionAtLeastFn)
+return;

Reverse these checks, please; IsOSVersionAtLeastFn is much cheaper to check and 
will predominantly be null.



Comment at: lib/CodeGen/CGObjC.cpp:3428
+  // CoreFoundation is not used in the code, the linker won't link the
+  // framework.
+  auto  = getLLVMContext();

Can you explain why compiler-rt has to load the symbol at runtime?  Is this 
just some compiler-rt testing thing?  Because it seems like a shame to pay a 
code-size cost — even a negligible one — for something like that.


Repository:
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https://reviews.llvm.org/D30977



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[PATCH] D30977: [CodeGen] Emit a CoreFoundation link guard when @available is used

2017-03-16 Thread Alex Lorenz via Phabricator via cfe-commits 
arphaman updated this revision to Diff 91977.
arphaman marked an inline comment as done.
arphaman added a comment.

The guard function is now `hidden`. I also adopted linker options as John 
suggested.


Repository:
  rL LLVM

https://reviews.llvm.org/D30977

Files:
  lib/CodeGen/CGObjC.cpp
  lib/CodeGen/CodeGenModule.cpp
  lib/CodeGen/CodeGenModule.h
  test/CodeGenObjC/availability-cf-link-guard.m

Index: test/CodeGenObjC/availability-cf-link-guard.m
===
--- /dev/null
+++ test/CodeGenObjC/availability-cf-link-guard.m
@@ -0,0 +1,45 @@
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.11 -emit-llvm -o - %s | FileCheck --check-prefixes=CHECK,CHECK_LINK_OPT %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.11 -emit-llvm -o - -D USE_BUILTIN %s | FileCheck --check-prefixes=CHECK,CHECK_LINK_OPT %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.11 -emit-llvm -o - -D DEF_CF %s | FileCheck --check-prefixes=CHECK_CF,CHECK_LINK_OPT %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.12 -emit-llvm -o - %s | FileCheck --check-prefix=CHECK_NO_GUARD %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux -emit-llvm -o - %s | FileCheck --check-prefix=CHECK_NO_GUARD %s
+
+#ifdef DEF_CF
+struct CFBundle;
+typedef struct CFBundle *CFBundleRef;
+unsigned CFBundleGetVersionNumber(CFBundleRef bundle);
+// CHECK_CF: declare i32 @CFBundleGetVersionNumber(%struct.CFBundle*)
+// CHECK_CF: @__clang_at_available_requires_core_foundation_framework
+// CHECK_CF-NEXT: call {{.*}}@CFBundleGetVersionNumber
+#endif
+
+void use_at_available() {
+#ifdef DEF_CF
+  CFBundleGetVersionNumber(0);
+#endif
+#ifdef USE_BUILTIN
+  if (__builtin_available(macos 10.12, *))
+;
+#else
+  if (@available(macos 10.12, *))
+;
+#endif
+}
+
+// CHECK: @llvm.compiler.used{{.*}}@__clang_at_available_requires_core_foundation_framework
+
+// CHECK: declare i32 @CFBundleGetVersionNumber(i8*)
+
+// CHECK-LABEL: linkonce hidden void @__clang_at_available_requires_core_foundation_framework
+// CHECK: call i32 @CFBundleGetVersionNumber(i8* null)
+// CHECK-NEXT: unreachable
+
+// CHECK_NO_GUARD-NOT: __clang_at_available_requires_core_foundation_framework
+// CHECK_NO_GUARD-NOT: CFBundleGetVersionNumber
+
+// CHECK_LINK_OPT: !"Linker Options", ![[OPTS:[0-9]+]]
+// CHECK_LINK_OPT: ![[OPTS]] = !{![[FRAMEWORK:[0-9]+]]
+// CHECK_LINK_OPT: ![[FRAMEWORK]] = !{!"-framework", !"CoreFoundation"}
+
+// CHECK_NO_GUARD-NOT: "Linker Options"
+// CHECK_NO_GUARD-NOT: CoreFoundation
Index: lib/CodeGen/CodeGenModule.h
===
--- lib/CodeGen/CodeGenModule.h
+++ lib/CodeGen/CodeGenModule.h
@@ -1288,6 +1288,10 @@
   /// Emit any vtables which we deferred and still have a use for.
   void EmitDeferredVTables();
 
+  /// Emit a dummy function that reference a CoreFoundation symbol when
+  /// @available is used on Darwin.
+  void emitAtAvailableLinkGuard();
+
   /// Emit the llvm.used and llvm.compiler.used metadata.
   void emitLLVMUsed();
 
Index: lib/CodeGen/CodeGenModule.cpp
===
--- lib/CodeGen/CodeGenModule.cpp
+++ lib/CodeGen/CodeGenModule.cpp
@@ -408,6 +408,7 @@
 CoverageMapping->emit();
   if (CodeGenOpts.SanitizeCfiCrossDso)
 CodeGenFunction(*this).EmitCfiCheckFail();
+  emitAtAvailableLinkGuard();
   emitLLVMUsed();
   if (SanStats)
 SanStats->finish();
Index: lib/CodeGen/CGObjC.cpp
===
--- lib/CodeGen/CGObjC.cpp
+++ lib/CodeGen/CGObjC.cpp
@@ -3416,4 +3416,37 @@
   return Builder.CreateICmpNE(CallRes, llvm::Constant::getNullValue(Int32Ty));
 }
 
+void CodeGenModule::emitAtAvailableLinkGuard() {
+  // @available requires CoreFoundation only on Darwin.
+  if (!Target.getTriple().isOSDarwin())
+return;
+  if (!IsOSVersionAtLeastFn)
+return;
+  // Add -framework CoreFoundation to the linker commands. We still want to
+  // emit the core foundation reference down below because otherwise if
+  // CoreFoundation is not used in the code, the linker won't link the
+  // framework.
+  auto  = getLLVMContext();
+  llvm::Metadata *Args[2] = {llvm::MDString::get(Context, "-framework"),
+ llvm::MDString::get(Context, "CoreFoundation")};
+  LinkerOptionsMetadata.push_back(llvm::MDNode::get(Context, Args));
+  // Emit a reference to a symbol from CoreFoundation to ensure that
+  // CoreFoundation is linked into the final binary.
+  llvm::FunctionType *FTy =
+  llvm::FunctionType::get(Int32Ty, {VoidPtrTy}, false);
+  llvm::Constant *CFFunc =
+  CreateRuntimeFunction(FTy, "CFBundleGetVersionNumber");
+
+  llvm::FunctionType *CheckFTy = llvm::FunctionType::get(VoidTy, {}, false);
+  llvm::Function *CFLinkCheckFunc = cast(CreateBuiltinFunction(
+  CheckFTy, "__clang_at_available_requires_core_foundation_framework"));
+

[PATCH] D30977: [CodeGen] Emit a CoreFoundation link guard when @available is used

2017-03-15 Thread Alex Lorenz via Phabricator via cfe-commits 
arphaman added inline comments.



Comment at: lib/CodeGen/CGObjC.cpp:3435
+  CheckFTy, "__clang_at_available_requires_core_foundation_framework"));
+  CFLinkCheckFunc->setLinkage(llvm::GlobalValue::LinkOnceAnyLinkage);
+  CodeGenFunction CGF(*this);

rjmccall wrote:
> Is this a public weak symbol?  Make it hidden, please.
> 
> Did you consider just adding "-framework CoreFoundation"  to the module link 
> options?
I'm not familiar with module link options, I'll look into them.


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https://reviews.llvm.org/D30977



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[PATCH] D30977: [CodeGen] Emit a CoreFoundation link guard when @available is used

2017-03-15 Thread John McCall via Phabricator via cfe-commits 
rjmccall added inline comments.



Comment at: lib/CodeGen/CGObjC.cpp:3435
+  CheckFTy, "__clang_at_available_requires_core_foundation_framework"));
+  CFLinkCheckFunc->setLinkage(llvm::GlobalValue::LinkOnceAnyLinkage);
+  CodeGenFunction CGF(*this);

Is this a public weak symbol?  Make it hidden, please.

Did you consider just adding "-framework CoreFoundation"  to the module link 
options?


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[PATCH] D30977: [CodeGen] Emit a CoreFoundation link guard when @available is used

2017-03-15 Thread Alex Lorenz via Phabricator via cfe-commits 
arphaman created this revision.

After r297760, __isOSVersionAtLeast in compiler-rt loads the CoreFoundation 
symbols at runtime. This means that `@available` will always fail when used in 
a binary without a linked CoreFoundation.

This patch forces Clang to emit a reference to a CoreFoundation symbol when 
`@available` is used to ensure that linking will fail when CoreFoundation isn't 
linked with the build product.


Repository:
  rL LLVM

https://reviews.llvm.org/D30977

Files:
  lib/CodeGen/CGObjC.cpp
  lib/CodeGen/CodeGenModule.cpp
  lib/CodeGen/CodeGenModule.h
  test/CodeGenObjC/availability-cf-link-guard.m

Index: test/CodeGenObjC/availability-cf-link-guard.m
===
--- /dev/null
+++ test/CodeGenObjC/availability-cf-link-guard.m
@@ -0,0 +1,38 @@
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.11 -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.11 -emit-llvm -o - -D USE_BUILTIN %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.11 -emit-llvm -o - -D DEF_CF %s | FileCheck --check-prefix=CHECK_CF %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.12 -emit-llvm -o - %s | FileCheck --check-prefix=CHECK_NO_GUARD %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux -emit-llvm -o - %s | FileCheck --check-prefix=CHECK_NO_GUARD %s
+
+#ifdef DEF_CF
+struct CFBundle;
+typedef struct CFBundle *CFBundleRef;
+unsigned CFBundleGetVersionNumber(CFBundleRef bundle);
+// CHECK_CF: declare i32 @CFBundleGetVersionNumber(%struct.CFBundle*)
+// CHECK_CF: @__clang_at_available_requires_core_foundation_framework
+// CHECK_CF-NEXT: call {{.*}}@CFBundleGetVersionNumber
+#endif
+
+void use_at_available() {
+#ifdef DEF_CF
+  CFBundleGetVersionNumber(0);
+#endif
+#ifdef USE_BUILTIN
+  if (__builtin_available(macos 10.12, *))
+;
+#else
+  if (@available(macos 10.12, *))
+;
+#endif
+}
+
+// CHECK: @llvm.compiler.used{{.*}}@__clang_at_available_requires_core_foundation_framework
+
+// CHECK: declare i32 @CFBundleGetVersionNumber(i8*)
+
+// CHECK-LABEL: linkonce void @__clang_at_available_requires_core_foundation_framework
+// CHECK: call i32 @CFBundleGetVersionNumber(i8* null)
+// CHECK-NEXT: unreachable
+
+// CHECK_NO_GUARD-NOT: __clang_at_available_requires_core_foundation_framework
+// CHECK_NO_GUARD-NOT: CFBundleGetVersionNumber
Index: lib/CodeGen/CodeGenModule.h
===
--- lib/CodeGen/CodeGenModule.h
+++ lib/CodeGen/CodeGenModule.h
@@ -1288,6 +1288,10 @@
   /// Emit any vtables which we deferred and still have a use for.
   void EmitDeferredVTables();
 
+  /// Emit a dummy function that reference a CoreFoundation symbol when
+  /// @available is used on Darwin.
+  void emitAtAvailableLinkGuard();
+
   /// Emit the llvm.used and llvm.compiler.used metadata.
   void emitLLVMUsed();
 
Index: lib/CodeGen/CodeGenModule.cpp
===
--- lib/CodeGen/CodeGenModule.cpp
+++ lib/CodeGen/CodeGenModule.cpp
@@ -408,6 +408,7 @@
 CoverageMapping->emit();
   if (CodeGenOpts.SanitizeCfiCrossDso)
 CodeGenFunction(*this).EmitCfiCheckFail();
+  emitAtAvailableLinkGuard();
   emitLLVMUsed();
   if (SanStats)
 SanStats->finish();
Index: lib/CodeGen/CGObjC.cpp
===
--- lib/CodeGen/CGObjC.cpp
+++ lib/CodeGen/CGObjC.cpp
@@ -3416,4 +3416,28 @@
   return Builder.CreateICmpNE(CallRes, llvm::Constant::getNullValue(Int32Ty));
 }
 
+void CodeGenModule::emitAtAvailableLinkGuard() {
+  // @available requires CoreFoundation only on Darwin.
+  if (!Target.getTriple().isOSDarwin())
+return;
+  if (!IsOSVersionAtLeastFn)
+return;
+  // Emit a reference to a symbol from CoreFoundation to ensure that
+  // CoreFoundation is linked into the final binary.
+  llvm::FunctionType *FTy =
+  llvm::FunctionType::get(Int32Ty, {VoidPtrTy}, false);
+  llvm::Constant *CFFunc =
+  CreateRuntimeFunction(FTy, "CFBundleGetVersionNumber");
+
+  llvm::FunctionType *CheckFTy = llvm::FunctionType::get(VoidTy, {}, false);
+  llvm::Function *CFLinkCheckFunc = cast(CreateBuiltinFunction(
+  CheckFTy, "__clang_at_available_requires_core_foundation_framework"));
+  CFLinkCheckFunc->setLinkage(llvm::GlobalValue::LinkOnceAnyLinkage);
+  CodeGenFunction CGF(*this);
+  CGF.Builder.SetInsertPoint(CGF.createBasicBlock("", CFLinkCheckFunc));
+  CGF.EmitNounwindRuntimeCall(CFFunc, llvm::Constant::getNullValue(VoidPtrTy));
+  CGF.Builder.CreateUnreachable();
+  addCompilerUsedGlobal(CFLinkCheckFunc);
+}
+
 CGObjCRuntime::~CGObjCRuntime() {}
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