[CodeGen][ObjC] Build the global block structure before emitting the body of global block invoke functions

[ahatanak]

Summary

This patch fixes an infinite loop in IRGen that occurs when compiling the following code:

void FUNC2() {
  static void (^const block1)(int) = ^(int a){
    if (a--)
      block1(a);
  };

When IRGen visits the call to "block1", it knows that it always calls the block defined in Func2 enclosing the call (because "block1" is const qualified), so it tries to emit the reference to "block1" as a constant and calls CodeGenModule::GetAddrOfGlobalBlock to get the address of the block. CodeGenModule::GetAddrOfGlobalBlock checks whether the block has already been emitted (calling getAddrOfGlobalBlockIfEmitted). If the block hasn't been emitted, it starts generating the block invoke function, which causes the infinite loop.

I believe this happens because clang's constant folding got smarter (see commit log of r290661, for example) and the call "refExpr->EvaluateAsRValue" in CodeGenFunction::tryEmitAsConstant returns true now as a result.

This patch prevents the infinite loop by building the global block in GenerateBlockFunction before it emits the IR of the body of the function.

rdar://problem/34541684

[rjmccall]

LGTM with one tweak.

lib/CodeGen/CGBlocks.cpp

1124

Please /*comment*/ the meaning of these bools.

lib/CodeGen/CGBlocks.cpp

 }
 
 llvm::Value *CodeGenFunction::EmitBlockLiteral(const CGBlockInfo &blockInfo) {
   // Using the computed layout, generate the actual block function.
   bool isLambdaConv = blockInfo.getBlockDecl()->isConversionFromLambda();
   llvm::Constant *blockFn
     = CodeGenFunction(CGM, true).GenerateBlockFunction(CurGD, blockInfo,
                                                        LocalDeclMap,
-                                                       isLambdaConv);
+                                                       isLambdaConv,
+                                                       blockInfo.CanBeGlobal);
   blockFn = llvm::ConstantExpr::getBitCast(blockFn, VoidPtrTy);
 
   // If there is nothing to capture, we can emit this as a global block.
   if (blockInfo.CanBeGlobal)
-    return buildGlobalBlock(CGM, blockInfo, blockFn);
+    return CGM.getAddrOfGlobalBlockIfEmitted(blockInfo.BlockExpression);
 
   // Otherwise, we have to emit this as a local block.
 
   llvm::Constant *isa =
       (!CGM.getContext().getLangOpts().OpenCL)
           ? CGM.getNSConcreteStackBlock()
           : CGM.getNullPointer(VoidPtrPtrTy,
                                CGM.getContext().getPointerType(
CodeGenModule::GetAddrOfGlobalBlock(const BlockExpr *BE,
 
   // Using that metadata, generate the actual block function.
   llvm::Constant *blockFn;
   {
     CodeGenFunction::DeclMapTy LocalDeclMap;
     blockFn = CodeGenFunction(*this).GenerateBlockFunction(GlobalDecl(),
                                                            blockInfo,
                                                            LocalDeclMap,
-                                                           false);
+                                                           false, true);
   }
-  blockFn = llvm::ConstantExpr::getBitCast(blockFn, VoidPtrTy);
 
-  return buildGlobalBlock(*this, blockInfo, blockFn);
+  return getAddrOfGlobalBlockIfEmitted(BE);
 }
 
 static llvm::Constant *buildGlobalBlock(CodeGenModule &CGM,
                                         const CGBlockInfo &blockInfo,
                                         llvm::Constant *blockFn) {
   assert(blockInfo.CanBeGlobal);
   // Callers should detect this case on their own: calling this function
   // generally requires computing layout information, which is a waste of time
Address CodeGenFunction::LoadBlockStruct() {
   assert(BlockPointer && "no block pointer set!");
   return Address(BlockPointer, BlockInfo->BlockAlign);
 }
 
 llvm::Function *
 CodeGenFunction::GenerateBlockFunction(GlobalDecl GD,
                                        const CGBlockInfo &blockInfo,
                                        const DeclMapTy &ldm,
-                                       bool IsLambdaConversionToBlock) {
+                                       bool IsLambdaConversionToBlock,
+                                       bool BuildGlobalBlock) {
   const BlockDecl *blockDecl = blockInfo.getBlockDecl();
 
   CurGD = GD;
 
   CurEHLocation = blockInfo.getBlockExpr()->getLocEnd();
   
   BlockInfo = &blockInfo;
 
CodeGenFunction::GenerateBlockFunction(GlobalDecl GD,
 
   llvm::FunctionType *fnLLVMType = CGM.getTypes().GetFunctionType(fnInfo);
 
   StringRef name = CGM.getBlockMangledName(GD, blockDecl);
   llvm::Function *fn = llvm::Function::Create(
       fnLLVMType, llvm::GlobalValue::InternalLinkage, name, &CGM.getModule());
   CGM.SetInternalFunctionAttributes(blockDecl, fn, fnInfo);
 
+  if (BuildGlobalBlock)
+    buildGlobalBlock(CGM, blockInfo,
+                     llvm::ConstantExpr::getBitCast(fn, VoidPtrTy));
+
   // Begin generating the function.
   StartFunction(blockDecl, fnType->getReturnType(), fn, fnInfo, args,
                 blockDecl->getLocation(),
                 blockInfo.getBlockExpr()->getBody()->getLocStart());
 
   // Okay.  Undo some of what StartFunction did.
 
   // At -O0 we generate an explicit alloca for the BlockPointer, so the RA

lib/CodeGen/CodeGenFunction.h

public:
   //===--------------------------------------------------------------------===//
 
   llvm::Value *EmitBlockLiteral(const BlockExpr *);
   static void destroyBlockInfos(CGBlockInfo *info);
 
   llvm::Function *GenerateBlockFunction(GlobalDecl GD,
                                         const CGBlockInfo &Info,
                                         const DeclMapTy &ldm,
-                                        bool IsLambdaConversionToBlock);
+                                        bool IsLambdaConversionToBlock,
+                                        bool BuildGlobalBlock);
 
   llvm::Constant *GenerateCopyHelperFunction(const CGBlockInfo &blockInfo);
   llvm::Constant *GenerateDestroyHelperFunction(const CGBlockInfo &blockInfo);
   llvm::Constant *GenerateObjCAtomicSetterCopyHelperFunction(
                                              const ObjCPropertyImplDecl *PID);
   llvm::Constant *GenerateObjCAtomicGetterCopyHelperFunction(
                                              const ObjCPropertyImplDecl *PID);
   llvm::Value *EmitBlockCopyAndAutorelease(llvm::Value *Block, QualType Ty);

test/CodeGen/mangle-blocks.c

 // RUN: %clang_cc1 -triple i386-apple-ios -fblocks -emit-llvm -o - %s | FileCheck %s
 
 void __assert_rtn(const char *, const char *, int, const char *)
     __attribute__ (( noreturn ));
 
 void (^mangle(void))(void) {
   return ^{
     void (^block)(void) = ^{
       __assert_rtn(__func__, __FILE__, __LINE__, "mangle");
     };
   };
 }
 
 // CHECK: @__func__.__mangle_block_invoke_2 = private unnamed_addr constant [22 x i8] c"mangle_block_invoke_2\00", align 1
-// CHECK: @.str = private unnamed_addr constant {{.*}}, align 1
-// CHECK: @.str.1 = private unnamed_addr constant [7 x i8] c"mangle\00", align 1
+// CHECK: @.str{{.*}} = private unnamed_addr constant {{.*}}, align 1
+// CHECK: @.str[[STR1:.*]] = private unnamed_addr constant [7 x i8] c"mangle\00", align 1
 
 // CHECK: define internal void @__mangle_block_invoke(i8* %.block_descriptor)
 
 // CHECK: define internal void @__mangle_block_invoke_2(i8* %.block_descriptor){{.*}}{
-// CHECK:   call void @__assert_rtn(i8* getelementptr inbounds ([22 x i8], [22 x i8]* @__func__.__mangle_block_invoke_2, i32 0, i32 0), i8* getelementptr inbounds {{.*}}, i32 9, i8* getelementptr inbounds ([7 x i8], [7 x i8]* @.str.1, i32 0, i32 0))
+// CHECK:   call void @__assert_rtn(i8* getelementptr inbounds ([22 x i8], [22 x i8]* @__func__.__mangle_block_invoke_2, i32 0, i32 0), i8* getelementptr inbounds {{.*}}, i32 9, i8* getelementptr inbounds ([7 x i8], [7 x i8]* @.str[[STR1]], i32 0, i32 0))
 // CHECK: }
 

test/CodeGenObjC/local-static-block.m

for(id rawAddress in addresses)
        separatedAddresses = ArrayRecurs((NSArray *)rawAddress, level+1);
      }
      return (NSArray *)0;
    };
    ArrayRecurs(address, level);
  }
 }
 
+void FUNC2() {
+  static void (^const block1)(int) = ^(int a){
+    if (a--)
+      block1(a);
+  };
+}
+
+// CHECK-LABEL-LP64: define void @FUNC2(
+// CHECK: define internal void @_block_invoke{{.*}}(
+// CHECK: call void %{{.*}}(i8* bitcast ({ i8**, i32, i32, i8*, %struct.__block_descriptor* }* @__block_literal_global{{.*}} to i8*), i32 %{{.*}})
+
 void FUNC1()
 {
  static  NSArray *(^ArrayRecurs)(NSArray *addresses, unsigned long level) = ^(NSArray *addresses, unsigned long level) {
 
   for(id rawAddress in addresses)
   {
    NSArray *separatedAddresses = ((NSArray*)0);
    separatedAddresses = ArrayRecurs((NSArray *)rawAddress, level+1);

test/CodeGenObjC/mangle-blocks.m

return ^() {
     void (^b)(void) = ^() {
       __assert_rtn(__func__, __FILE__, __LINE__, "mangle");
     };
   };
 }
 @end
 
 // CHECK: @"__func__.__14-[Test mangle]_block_invoke_2" = private unnamed_addr constant [30 x i8] c"-[Test mangle]_block_invoke_2\00", align 1
-// CHECK: @.str = private unnamed_addr constant {{.*}}, align 1
-// CHECK: @.str.1 = private unnamed_addr constant [7 x i8] c"mangle\00", align 1
+// CHECK: @.str{{.*}} = private unnamed_addr constant {{.*}}, align 1
+// CHECK: @.str[[STR1:.*]] = private unnamed_addr constant [7 x i8] c"mangle\00", align 1
 
 // CHECK: define internal void @"__14-[Test mangle]_block_invoke"(i8* %.block_descriptor)
 
 // CHECK: define internal void @"__14-[Test mangle]_block_invoke_2"(i8* %.block_descriptor){{.*}}{
-// CHECK: call void @__assert_rtn(i8* getelementptr inbounds ([30 x i8], [30 x i8]* @"__func__.__14-[Test mangle]_block_invoke_2", i32 0, i32 0), i8* getelementptr inbounds {{.*}}, i32 14, i8* getelementptr inbounds ([7 x i8], [7 x i8]* @.str.1, i32 0, i32 0))
+// CHECK: call void @__assert_rtn(i8* getelementptr inbounds ([30 x i8], [30 x i8]* @"__func__.__14-[Test mangle]_block_invoke_2", i32 0, i32 0), i8* getelementptr inbounds {{.*}}, i32 14, i8* getelementptr inbounds ([7 x i8], [7 x i8]* @.str[[STR1]], i32 0, i32 0))
 // CHECK: }