Expose CastInst::getCastOpcode in C API

[jackoalan]

Summary

Users of LLVMBuildCast currently need to implement their own logic to determine the best cast opcode. In cases where the source value and destination type is known, LLVM already has the CastInst::getCastOpcode function to determine the opcode based on type combinations.

This simply exposes the existing function to users of the C API.

[deadalnix]

It would be good to have a test case for this.

[jackoalan]

Add unit test

[jackoalan]

ping

[jackoalan]

Rebase

llvm/docs/ReleaseNotes.rst

 Changes to the OCaml bindings
 -----------------------------
 
 
 
 Changes to the C API
 --------------------
 
+* Add `LLVMGetCastOpcode` function to aid users of `LLVMBuildCast` resolve 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
 --------------------------
 
 
 Changes to the DAG infrastructure
 ---------------------------------
 

llvm/include/llvm-c/Core.h

LLVMValueRef LLVMBuildIntCast2(LLVMBuilderRef, LLVMValueRef Val,
                                const char *Name);
 LLVMValueRef LLVMBuildFPCast(LLVMBuilderRef, LLVMValueRef Val,
                              LLVMTypeRef DestTy, const char *Name);
 
 /** Deprecated: This cast is always signed. Use LLVMBuildIntCast2 instead. */
 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,
                            const char *Name);
 LLVMValueRef LLVMBuildFCmp(LLVMBuilderRef, LLVMRealPredicate Op,
                            LLVMValueRef LHS, LLVMValueRef RHS,
                            const char *Name);
 

llvm/lib/IR/Core.cpp

return wrap(unwrap(B)->CreateIntCast(unwrap(Val), unwrap(DestTy),
                                        /*isSigned*/true, Name));
 }
 
 LLVMValueRef LLVMBuildFPCast(LLVMBuilderRef B, LLVMValueRef Val,
                              LLVMTypeRef DestTy, const char *Name) {
   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,
                            LLVMValueRef LHS, LLVMValueRef RHS,
                            const char *Name) {
   return wrap(unwrap(B)->CreateICmp(static_cast<ICmpInst::Predicate>(Op),
                                     unwrap(LHS), unwrap(RHS), Name));
 }