[PATCH] D14615: [C++] Add the "norecurse" attribute to main() if in C++ mode

[James Molloy via cfe-commits]

jmolloy created this revision.
jmolloy added a reviewer: aaron.ballman.
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jmolloy set the repository for this revision to rL LLVM.

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.

Repository:
  rL LLVM

http://reviews.llvm.org/D14615

Files:
  lib/CodeGen/CodeGenFunction.cpp
  test/CodeGenCXX/main-norecurse.cpp
  test/CodeGenObjC/objc-literal-tests.m

Index: test/CodeGenObjC/objc-literal-tests.m
===================================================================
--- test/CodeGenObjC/objc-literal-tests.m
+++ test/CodeGenObjC/objc-literal-tests.m
@@ -94,4 +94,4 @@
   bar(^(void) { return YES; });
 }
 
-// CHECK: attributes [[NUW]] = { nounwind{{.*}} }
+// CHECK: attributes [[NUW]] = { {{(norecurse )?}}nounwind{{.*}} }
Index: test/CodeGenCXX/main-norecurse.cpp
===================================================================
--- /dev/null
+++ test/CodeGenCXX/main-norecurse.cpp
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -emit-llvm %s -o -
+
+// CHECK: define i{{.*}} @main({{.*}}) [[A:#.*]]
+int main(int argc, char **argv) {
+    return 1;
+}
+
+// CHECK: attribute [[A]] = attributes { norecurse{{.*}} }
Index: lib/CodeGen/CodeGenFunction.cpp
===================================================================
--- lib/CodeGen/CodeGenFunction.cpp
+++ lib/CodeGen/CodeGenFunction.cpp
@@ -716,6 +716,14 @@
     }
   }
 
+  // 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


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