Incorrect parsing of CST_CODE_CE_GEP_WITH_INRANGE_INDEX's type

[RyanGlScott]

While investigating the code for parsing ConstGEP, I noticed this suspicious-looking TODO:

llvm-pretty-bc-parser/src/Data/LLVM/BitCode/IR/Constants.hs

Lines 457 to 473 in 0946cbe

	parseCeGep :: Bool -> Maybe Word64 -> ValueTable -> Record -> Parse PValue
	parseCeGep isInbounds mInrangeIdx t r = do
	let isExplicit = odd (length (recordFields r)) -- TODO: is this right for INRANGE_INDEX?
	firstIdx = if isJust mInrangeIdx then 2 else if isExplicit then 1 else 0
	field = parseField r
	loop n = do
	ty <- getType =<< field n numeric
	elt <- field (n+1) numeric
	rest <- loop (n+2) `mplus` return []
	cxt <- getContext
	return (Typed ty (typedValue (forwardRef cxt elt t)) : rest)
	mPointeeType <-
	if isExplicit
	then Just <$> (getType =<< field 0 numeric)
	else pure Nothing
	args <- loop firstIdx
	return $! ValConstExpr (ConstGEP isInbounds mInrangeIdx mPointeeType args)

And indeed, this code isn't right for CST_CODE_CE_GEP_WITH_INRANGE_INDEX. As proof, if you take this .ll file (taken from here):

define i8** @constexpr() {
  ret i8** getelementptr inbounds ({ [4 x i8*], [4 x i8*] }, { [4 x i8*], [4 x i8*] }* null, i32 0, inrange i32 1, i32 2)
}

Convert it to a .bc file:

$ llvm-as test.ll -o test.bc

And then load it with llvm-pretty-bc-parser, you will get:

λ> parseBitCodeFromFile "test.bc"
Right (Module {modSourceName = Just "test.ll", modTriple = TargetTriple {ttArch = UnknownArch, ttSubArch = NoSubArch, ttVendor = UnknownVendor, ttOS = UnknownOS, ttEnv = UnknownEnvironment, ttObjFmt = UnknownObjectFormat}, modDataLayout = [], modTypes = [], modNamedMd = [], modUnnamedMd = [], modComdat = fromList [], modGlobals = [], modDeclares = [], modDefines = [Define {defLinkage = Nothing, defVisibility = Just DefaultVisibility, defRetType = PtrTo (PtrTo (PrimType (Integer 8))), defName = Symbol "constexpr", defArgs = [], defVarArgs = False, defAttrs = [], defSection = Nothing, defGC = Nothing, defBody = [BasicBlock {bbLabel = Just (Anon 0), bbStmts = [Effect (Ret (Typed {typedType = PtrTo (PtrTo (PrimType (Integer 8))), typedValue = ValConstExpr (ConstGEP True (Just 1) Nothing [Typed {typedType = PtrTo (Struct [Array 4 (PtrTo (PrimType (Integer 8))),Array 4 (PtrTo (PrimType (Integer 8)))]), typedValue = ValNull},Typed {typedType = PrimType (Integer 32), typedValue = ValInteger 0},Typed {typedType = PrimType (Integer 32), typedValue = ValInteger 1},Typed {typedType = PrimType (Integer 32), typedValue = ValInteger 2}])})) []]}], defMetadata = fromList [], defComdat = Nothing}], modInlineAsm = [], modAliases = []})

The incorrect part is the Nothing in ConstGEP True (Just 1) Nothing ..., indicating that there is no explicit type to use as a basis for calculations. This is incorrect because CST_CODE_CE_GEP_WITH_INRANGE_INDEX always includes an explicit type, as indicated here. The correct thing to do would be to mirror how LLVM's own bicode reader works here.