Use the actual ABI-determined C calling convention for runtime

calls and declarations.

LLVM has a default CC determined by the target triple.  This is
not always the actual default CC for the ABI we've been asked to
target, and so we sometimes find ourselves annotating all user
functions with an explicit calling convention.  Since these
calling conventions usually agree for the simple set of argument
types passed to most runtime functions, using the LLVM-default CC
in principle has no effect.  However, the LLVM optimizer goes
into histrionics if it sees this kind of formal CC mismatch,
since it has no concept of CC compatibility.  Therefore, if this
module happens to define the "runtime" function, or got LTO'ed
with such a definition, we can miscompile;  so it's quite
important to get this right.

Defining runtime functions locally is quite common in embedded
applications.

llvm-svn: 176286

1 files changed, 9 insertions, 2 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 2d3b5076b50..cae2c867db2 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -107,6 +107,8 @@ CodeGenModule::CodeGenModule(ASTContext &C, const CodeGenOptions &CGO,
   Int8PtrTy = Int8Ty->getPointerTo(0);
   Int8PtrPtrTy = Int8PtrTy->getPointerTo(0);
 
+  RuntimeCC = getTargetCodeGenInfo().getABIInfo().getRuntimeCC();
+
   if (LangOpts.ObjC1)
     createObjCRuntime();
   if (LangOpts.OpenCL)
@@ -1354,8 +1356,13 @@ llvm::Constant *
 CodeGenModule::CreateRuntimeFunction(llvm::FunctionType *FTy,
                                      StringRef Name,
                                      llvm::AttributeSet ExtraAttrs) {
-  return GetOrCreateLLVMFunction(Name, FTy, GlobalDecl(), /*ForVTable=*/false,
-                                 ExtraAttrs);
+  llvm::Constant *C
+    = GetOrCreateLLVMFunction(Name, FTy, GlobalDecl(), /*ForVTable=*/false,
+                              ExtraAttrs);
+  if (llvm::Function *F = dyn_cast<llvm::Function>(C))
+    if (F->empty())
+      F->setCallingConv(getRuntimeCC());
+  return C;
 }
 
 /// isTypeConstant - Determine whether an object of this type can be emitted