Index: llvm/include/llvm/IR/CallSite.h
===================================================================
--- llvm/include/llvm/IR/CallSite.h
+++ llvm/include/llvm/IR/CallSite.h
@@ -121,9 +121,13 @@
     return true;
   }
 
-  /// Set the callee to the specified value.
+  /// Set the callee to the specified value.  Unlike the function of the same
+  /// name on CallBase, does not modify the type!
   void setCalledFunction(Value *V) {
     assert(getInstruction() && "Not a call or invoke instruction!");
+    assert(cast<PointerType>(V->getType())->getElementType() ==
+               cast<CallBase>(getInstruction())->getFunctionType() &&
+           "New callee type does not match FunctionType on call");
     *getCallee() = V;
   }
 
Index: llvm/include/llvm/IR/InstrTypes.h
===================================================================
--- llvm/include/llvm/IR/InstrTypes.h
+++ llvm/include/llvm/IR/InstrTypes.h
@@ -27,6 +27,7 @@
 #include "llvm/IR/CallingConv.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Function.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/OperandTraits.h"
@@ -1206,10 +1207,8 @@
   void setCalledOperand(Value *V) { Op<CalledOperandOpEndIdx>() = V; }
 
   /// Sets the function called, including updating the function type.
-  void setCalledFunction(Value *Fn) {
-    setCalledFunction(
-        cast<FunctionType>(cast<PointerType>(Fn->getType())->getElementType()),
-        Fn);
+  void setCalledFunction(Function *Fn) {
+    setCalledFunction(Fn->getFunctionType(), Fn);
   }
 
   /// Sets the function called, including updating to the specified function
@@ -1218,6 +1217,9 @@
     this->FTy = FTy;
     assert(FTy == cast<FunctionType>(
                       cast<PointerType>(Fn->getType())->getElementType()));
+    // This function doesn't mutate the return type, only the function
+    // type. Seems broken, but I'm just gonna stick an assert in for now.
+    assert(getType() == FTy->getReturnType());
     setCalledOperand(Fn);
   }
 
Index: llvm/lib/Target/AMDGPU/AMDGPULibCalls.cpp
===================================================================
--- llvm/lib/Target/AMDGPU/AMDGPULibCalls.cpp
+++ llvm/lib/Target/AMDGPU/AMDGPULibCalls.cpp
@@ -552,7 +552,7 @@
     return sincosUseNative(aCI, FInfo);
 
   FInfo.setPrefix(AMDGPULibFunc::NATIVE);
-  Constant *F = getFunction(aCI->getModule(), FInfo);
+  Function *F = getFunction(aCI->getModule(), FInfo);
   if (!F)
     return false;
 
@@ -792,7 +792,7 @@
 
   AMDGPULibFunc nf = FInfo;
   nf.setPrefix(AMDGPULibFunc::NATIVE);
-  if (Constant *FPExpr = getFunction(M, nf)) {
+  if (Function *FPExpr = getFunction(M, nf)) {
     LLVM_DEBUG(dbgs() << "AMDIC: " << *CI << " ---> ");
 
     CI->setCalledFunction(FPExpr);
Index: llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -4200,7 +4200,8 @@
       // We cannot remove an invoke, because it would change the CFG, just
       // change the callee to a null pointer.
       cast<InvokeInst>(OldCall)->setCalledFunction(
-                                    Constant::getNullValue(CalleeF->getType()));
+          CalleeF->getFunctionType(),
+          Constant::getNullValue(CalleeF->getType()));
       return nullptr;
     }
   }
Index: llvm/lib/Transforms/ObjCARC/ObjCARCContract.cpp
===================================================================
--- llvm/lib/Transforms/ObjCARC/ObjCARCContract.cpp
+++ llvm/lib/Transforms/ObjCARC/ObjCARCContract.cpp
@@ -139,7 +139,7 @@
 
   // We do not have to worry about tail calls/does not throw since
   // retain/retainRV have the same properties.
-  Constant *Decl = EP.get(ARCRuntimeEntryPointKind::RetainRV);
+  Function *Decl = EP.get(ARCRuntimeEntryPointKind::RetainRV);
   cast<CallInst>(Retain)->setCalledFunction(Decl);
 
   LLVM_DEBUG(dbgs() << "New: " << *Retain << "\n");
@@ -188,7 +188,7 @@
                        "        Retain: "
                     << *Retain << "\n");
 
-  Constant *Decl = EP.get(Class == ARCInstKind::AutoreleaseRV
+  Function *Decl = EP.get(Class == ARCInstKind::AutoreleaseRV
                               ? ARCRuntimeEntryPointKind::RetainAutoreleaseRV
                               : ARCRuntimeEntryPointKind::RetainAutorelease);
   Retain->setCalledFunction(Decl);
Index: llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
===================================================================
--- llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
+++ llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
@@ -641,7 +641,7 @@
                        "Old = "
                     << *RetainRV << "\n");
 
-  Constant *NewDecl = EP.get(ARCRuntimeEntryPointKind::Retain);
+  Function *NewDecl = EP.get(ARCRuntimeEntryPointKind::Retain);
   cast<CallInst>(RetainRV)->setCalledFunction(NewDecl);
 
   LLVM_DEBUG(dbgs() << "New = " << *RetainRV << "\n");
@@ -690,7 +690,7 @@
              << *AutoreleaseRV << "\n");
 
   CallInst *AutoreleaseRVCI = cast<CallInst>(AutoreleaseRV);
-  Constant *NewDecl = EP.get(ARCRuntimeEntryPointKind::Autorelease);
+  Function *NewDecl = EP.get(ARCRuntimeEntryPointKind::Autorelease);
   AutoreleaseRVCI->setCalledFunction(NewDecl);
   AutoreleaseRVCI->setTailCall(false); // Never tail call objc_autorelease.
   Class = ARCInstKind::Autorelease;
Index: llvm/lib/Transforms/Utils/CallPromotionUtils.cpp
===================================================================
--- llvm/lib/Transforms/Utils/CallPromotionUtils.cpp
+++ llvm/lib/Transforms/Utils/CallPromotionUtils.cpp
@@ -366,8 +366,9 @@
                                CastInst **RetBitCast) {
   assert(!CS.getCalledFunction() && "Only indirect call sites can be promoted");
 
-  // Set the called function of the call site to be the given callee.
-  CS.setCalledFunction(Callee);
+  // Set the called function of the call site to be the given callee (but don't
+  // change the type).
+  cast<CallBase>(CS.getInstruction())->setCalledOperand(Callee);
 
   // Since the call site will no longer be direct, we must clear metadata that
   // is only appropriate for indirect calls. This includes !prof and !callees
Index: llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -2035,7 +2035,7 @@
     Constant *IPrintFFn =
         M->getOrInsertFunction("iprintf", FT, Callee->getAttributes());
     CallInst *New = cast<CallInst>(CI->clone());
-    New->setCalledFunction(IPrintFFn);
+    New->setCalledFunction(FT, IPrintFFn);
     B.Insert(New);
     return New;
   }
@@ -2114,7 +2114,7 @@
     Constant *SIPrintFFn =
         M->getOrInsertFunction("siprintf", FT, Callee->getAttributes());
     CallInst *New = cast<CallInst>(CI->clone());
-    New->setCalledFunction(SIPrintFFn);
+    New->setCalledFunction(FT, SIPrintFFn);
     B.Insert(New);
     return New;
   }
@@ -2271,7 +2271,7 @@
     Constant *FIPrintFFn =
         M->getOrInsertFunction("fiprintf", FT, Callee->getAttributes());
     CallInst *New = cast<CallInst>(CI->clone());
-    New->setCalledFunction(FIPrintFFn);
+    New->setCalledFunction(FT, FIPrintFFn);
     B.Insert(New);
     return New;
   }