[C++] Add the "norecurse" attribute to main() if in C++ mode

[jmolloy]

Summary

The C++ spec (3.6.1.3) says "The function main shall not be used within a program". This implies that it cannot recurse, so add the norecurse attribute to help the midend out a bit.

[jmolloy]

test/CodeGenCXX/main-norecurse.cpp

2

Wow, I managed to forget in my copy-paste from another test to add "| FileCheck %s" here.

I'll update this before committing.

[aaron.ballman]

lib/CodeGen/CodeGenFunction.cpp

721

Missing a period at the end of the sentence.

test/CodeGenCXX/main-norecurse.cpp

2

Missing FileCheck?

[aaron.ballman]

After fixing the FileCheck and grammar issues, LGTM!

[jmolloy]

Hi Aaron,

Thanks, this should all be fixed now.

Cheers,

James

[aaron.ballman]

Yup. LG, thanks!

[jmolloy]

Thanks Aaron, committed in r252902.

lib/CodeGen/CodeGenFunction.cpp

if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(D)) {
         llvm::Constant *PrologueStructElems[] = { PrologueSig, FTRTTIConst };
         llvm::Constant *PrologueStructConst =
             llvm::ConstantStruct::getAnon(PrologueStructElems, /*Packed=*/true);
         Fn->setPrologueData(PrologueStructConst);
       }
     }
   }
 
+  // If we're in C++ mode and the function name is "main", it is guaranteed
+  // to be norecurse by the standard (3.6.1.3 "The function main shall not be
+  // used within a program").
+  if (getLangOpts().CPlusPlus)
+    if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(D))
+      if (FD->isMain())
+        Fn->addFnAttr(llvm::Attribute::NoRecurse);
+  
   llvm::BasicBlock *EntryBB = createBasicBlock("entry", CurFn);
 
   // Create a marker to make it easy to insert allocas into the entryblock
   // later.  Don't create this with the builder, because we don't want it
   // folded.
   llvm::Value *Undef = llvm::UndefValue::get(Int32Ty);
   AllocaInsertPt = new llvm::BitCastInst(Undef, Int32Ty, "", EntryBB);
   if (Builder.isNamePreserving())

test/CodeGenCXX/main-norecurse.cpp

+// RUN: %clang_cc1 -emit-llvm %s -o - | FileCheck %s
+
+// CHECK: define i{{.*}} @main({{.*}}) #0
+int main(int argc, char **argv) {
+    return 1;
+}
+
+// CHECK: attributes #0 = { norecurse{{.*}} }

test/CodeGenObjC/objc-literal-tests.m

 // rdar://10579122
 typedef BOOL (^foo)(void);
 extern void bar(foo a);
 
 void baz(void) {
   bar(^(void) { return YES; });
 }
 
-// CHECK: attributes [[NUW]] = { nounwind{{.*}} }
+// CHECK: attributes [[NUW]] = { {{(norecurse )?}}nounwind{{.*}} }