From: Benjamin Kramer <benny.kra@googlemail.com>
Date: Sun, 3 Feb 2013 17:44:25 +0000 (+0000)
Subject: CodeGen: Mark the runtime function __dynamic_cast as readonly & nounwind.
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=21f6b39cca88f0a027c6f5cde24575165c2d5e40;p=clang

CodeGen: Mark the runtime function __dynamic_cast as readonly & nounwind.

This allows the optimizer to CSE dynamic_casts.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174289 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/CGExprCXX.cpp b/lib/CodeGen/CGExprCXX.cpp
index 8b7f2342c4..853e25ec8c 100644
--- a/lib/CodeGen/CGExprCXX.cpp
+++ b/lib/CodeGen/CGExprCXX.cpp
@@ -1689,11 +1689,16 @@ static llvm::Constant *getDynamicCastFn(CodeGenFunction &CGF) {
     CGF.ConvertType(CGF.getContext().getPointerDiffType());
 
   llvm::Type *Args[4] = { Int8PtrTy, Int8PtrTy, Int8PtrTy, PtrDiffTy };
-  
-  llvm::FunctionType *FTy =
-    llvm::FunctionType::get(Int8PtrTy, Args, false);
-  
-  return CGF.CGM.CreateRuntimeFunction(FTy, "__dynamic_cast");
+
+  llvm::FunctionType *FTy = llvm::FunctionType::get(Int8PtrTy, Args, false);
+
+  // Mark the function as nounwind readonly.
+  llvm::Attribute::AttrKind FuncAttrs[] = { llvm::Attribute::NoUnwind,
+                                            llvm::Attribute::ReadOnly };
+  llvm::AttributeSet Attrs = llvm::AttributeSet::get(
+      CGF.getLLVMContext(), llvm::AttributeSet::FunctionIndex, FuncAttrs);
+
+  return CGF.CGM.CreateRuntimeFunction(FTy, "__dynamic_cast", Attrs);
 }
 
 static llvm::Constant *getBadCastFn(CodeGenFunction &CGF) {
diff --git a/test/CodeGenCXX/dynamic-cast.cpp b/test/CodeGenCXX/dynamic-cast.cpp
index 813e36e941..77cfce1d46 100644
--- a/test/CodeGenCXX/dynamic-cast.cpp
+++ b/test/CodeGenCXX/dynamic-cast.cpp
@@ -16,3 +16,5 @@ const B& f(A *a) {
   }
   return fail;
 }
+
+// CHECK: declare i8* @__dynamic_cast(i8*, i8*, i8*, i64) nounwind readonly