Index: llvm/docs/ReleaseNotes.rst
===================================================================
--- llvm/docs/ReleaseNotes.rst
+++ llvm/docs/ReleaseNotes.rst
@@ -130,6 +130,9 @@
 
 * ``LLVMSetInstDebugLocation`` has been deprecated in favor of the more general
   ``LLVMAddMetadataToInst``.
+* Add ``LLVMGetCastOpcode`` function to aid users of ``LLVMBuildCast`` in
+  resolving the best cast operation given a source value and destination type.
+  This function is a direct wrapper of ``CastInst::getCastOpcode``.
 
 Changes to the Go bindings
 --------------------------
Index: llvm/include/llvm-c/Core.h
===================================================================
--- llvm/include/llvm-c/Core.h
+++ llvm/include/llvm-c/Core.h
@@ -3950,6 +3950,9 @@
 LLVMValueRef LLVMBuildIntCast(LLVMBuilderRef, LLVMValueRef Val, /*Signed cast!*/
                               LLVMTypeRef DestTy, const char *Name);
 
+LLVMOpcode LLVMGetCastOpcode(LLVMValueRef Src, LLVMBool SrcIsSigned,
+                             LLVMTypeRef DestTy, LLVMBool DestIsSigned);
+
 /* Comparisons */
 LLVMValueRef LLVMBuildICmp(LLVMBuilderRef, LLVMIntPredicate Op,
                            LLVMValueRef LHS, LLVMValueRef RHS,
Index: llvm/lib/IR/Core.cpp
===================================================================
--- llvm/lib/IR/Core.cpp
+++ llvm/lib/IR/Core.cpp
@@ -3891,6 +3891,12 @@
   return wrap(unwrap(B)->CreateFPCast(unwrap(Val), unwrap(DestTy), Name));
 }
 
+LLVMOpcode LLVMGetCastOpcode(LLVMValueRef Src, LLVMBool SrcIsSigned,
+                             LLVMTypeRef DestTy, LLVMBool DestIsSigned) {
+  return map_to_llvmopcode(CastInst::getCastOpcode(
+      unwrap(Src), SrcIsSigned, unwrap(DestTy), DestIsSigned));
+}
+
 /*--.. Comparisons .........................................................--*/
 
 LLVMValueRef LLVMBuildICmp(LLVMBuilderRef B, LLVMIntPredicate Op,
Index: llvm/unittests/IR/InstructionsTest.cpp
===================================================================
--- llvm/unittests/IR/InstructionsTest.cpp
+++ llvm/unittests/IR/InstructionsTest.cpp
@@ -6,10 +6,11 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "llvm/AsmParser/Parser.h"
 #include "llvm/IR/Instructions.h"
+#include "llvm-c/Core.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Analysis/ValueTracking.h"
+#include "llvm/AsmParser/Parser.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
@@ -388,6 +389,67 @@
   delete BB;
 }
 
+TEST(InstructionsTest, CastCAPI) {
+  LLVMContext C;
+
+  Type *Int8Ty = Type::getInt8Ty(C);
+  Type *Int32Ty = Type::getInt32Ty(C);
+  Type *Int64Ty = Type::getInt64Ty(C);
+
+  Type *FloatTy = Type::getFloatTy(C);
+  Type *DoubleTy = Type::getDoubleTy(C);
+
+  Type *Int8PtrTy = PointerType::get(Int8Ty, 0);
+  Type *Int32PtrTy = PointerType::get(Int32Ty, 0);
+
+  const Constant *C8 = Constant::getNullValue(Int8Ty);
+  const Constant *C64 = Constant::getNullValue(Int64Ty);
+
+  EXPECT_EQ(LLVMBitCast,
+            LLVMGetCastOpcode(wrap(C64), true, wrap(Int64Ty), true));
+  EXPECT_EQ(LLVMTrunc, LLVMGetCastOpcode(wrap(C64), true, wrap(Int8Ty), true));
+  EXPECT_EQ(LLVMSExt, LLVMGetCastOpcode(wrap(C8), true, wrap(Int64Ty), true));
+  EXPECT_EQ(LLVMZExt, LLVMGetCastOpcode(wrap(C8), false, wrap(Int64Ty), true));
+
+  const Constant *CF32 = Constant::getNullValue(FloatTy);
+  const Constant *CF64 = Constant::getNullValue(DoubleTy);
+
+  EXPECT_EQ(LLVMFPToUI,
+            LLVMGetCastOpcode(wrap(CF32), true, wrap(Int8Ty), false));
+  EXPECT_EQ(LLVMFPToSI,
+            LLVMGetCastOpcode(wrap(CF32), true, wrap(Int8Ty), true));
+  EXPECT_EQ(LLVMUIToFP,
+            LLVMGetCastOpcode(wrap(C8), false, wrap(FloatTy), true));
+  EXPECT_EQ(LLVMSIToFP, LLVMGetCastOpcode(wrap(C8), true, wrap(FloatTy), true));
+  EXPECT_EQ(LLVMFPTrunc,
+            LLVMGetCastOpcode(wrap(CF64), true, wrap(FloatTy), true));
+  EXPECT_EQ(LLVMFPExt,
+            LLVMGetCastOpcode(wrap(CF32), true, wrap(DoubleTy), true));
+
+  const Constant *CPtr8 = Constant::getNullValue(Int8PtrTy);
+
+  EXPECT_EQ(LLVMPtrToInt,
+            LLVMGetCastOpcode(wrap(CPtr8), true, wrap(Int8Ty), true));
+  EXPECT_EQ(LLVMIntToPtr,
+            LLVMGetCastOpcode(wrap(C8), true, wrap(Int8PtrTy), true));
+
+  Type *V8x8Ty = FixedVectorType::get(Int8Ty, 8);
+  Type *V8x64Ty = FixedVectorType::get(Int64Ty, 8);
+  const Constant *CV8 = Constant::getNullValue(V8x8Ty);
+  const Constant *CV64 = Constant::getNullValue(V8x64Ty);
+
+  EXPECT_EQ(LLVMTrunc, LLVMGetCastOpcode(wrap(CV64), true, wrap(V8x8Ty), true));
+  EXPECT_EQ(LLVMSExt, LLVMGetCastOpcode(wrap(CV8), true, wrap(V8x64Ty), true));
+
+  Type *Int32PtrAS1Ty = PointerType::get(Int32Ty, 1);
+  Type *V2Int32PtrAS1Ty = FixedVectorType::get(Int32PtrAS1Ty, 2);
+  Type *V2Int32PtrTy = FixedVectorType::get(Int32PtrTy, 2);
+  const Constant *CV2ptr32 = Constant::getNullValue(V2Int32PtrTy);
+
+  EXPECT_EQ(LLVMAddrSpaceCast, LLVMGetCastOpcode(wrap(CV2ptr32), true,
+                                                 wrap(V2Int32PtrAS1Ty), true));
+}
+
 TEST(InstructionsTest, VectorGep) {
   LLVMContext C;