compiler: rename getZeroValue to llvm.ConstNull

It does the same thing but should be more complete, and it probably is
faster as well (just one CGo call instead of several).

interp/utils.go

@@ -16,50 +16,6 @@ func getUses(value llvm.Value) []llvm.Value {
 	return uses
 }
 
-// Return a zero LLVM value for any LLVM type. Setting this value as an
-// initializer has the same effect as setting 'zeroinitializer' on a value.
-// Sadly, I haven't found a way to do it directly with the Go API but this works
-// just fine.
-func getZeroValue(typ llvm.Type) llvm.Value {
-	switch typ.TypeKind() {
-	case llvm.ArrayTypeKind:
-		subTyp := typ.ElementType()
-		subVal := getZeroValue(subTyp)
-		vals := make([]llvm.Value, typ.ArrayLength())
-		for i := range vals {
-			vals[i] = subVal
-		}
-		return llvm.ConstArray(subTyp, vals)
-	case llvm.FloatTypeKind, llvm.DoubleTypeKind:
-		return llvm.ConstFloat(typ, 0.0)
-	case llvm.IntegerTypeKind:
-		return llvm.ConstInt(typ, 0, false)
-	case llvm.PointerTypeKind:
-		return llvm.ConstPointerNull(typ)
-	case llvm.StructTypeKind:
-		types := typ.StructElementTypes()
-		vals := make([]llvm.Value, len(types))
-		for i, subTyp := range types {
-			val := getZeroValue(subTyp)
-			vals[i] = val
-		}
-		if typ.StructName() != "" {
-			return llvm.ConstNamedStruct(typ, vals)
-		} else {
-			return typ.Context().ConstStruct(vals, false)
-		}
-	case llvm.VectorTypeKind:
-		zero := getZeroValue(typ.ElementType())
-		vals := make([]llvm.Value, typ.VectorSize())
-		for i := range vals {
-			vals[i] = zero
-		}
-		return llvm.ConstVector(vals, false)
-	default:
-		panic("interp: unknown LLVM type: " + typ.String())
-	}
-}
-
 // getStringBytes loads the byte slice of a Go string represented as a
 // {ptr, len} pair.
 func getStringBytes(strPtr Value, strLen llvm.Value) []byte {