+ int compare(const BasicBlock *BBL, const BasicBlock *BBR);
+
+ /// Constants comparison.
+ /// Its analog to lexicographical comparison between hypothetical numbers
+ /// of next format:
+ /// <bitcastability-trait><raw-bit-contents>
+ ///
+ /// 1. Bitcastability.
+ /// Check whether L's type could be losslessly bitcasted to R's type.
+ /// On this stage method, in case when lossless bitcast is not possible
+ /// method returns -1 or 1, thus also defining which type is greater in
+ /// context of bitcastability.
+ /// Stage 0: If types are equal in terms of cmpTypes, then we can go straight
+ /// to the contents comparison.
+ /// If types differ, remember types comparison result and check
+ /// whether we still can bitcast types.
+ /// Stage 1: Types that satisfies isFirstClassType conditions are always
+ /// greater then others.
+ /// Stage 2: Vector is greater then non-vector.
+ /// If both types are vectors, then vector with greater bitwidth is
+ /// greater.
+ /// If both types are vectors with the same bitwidth, then types
+ /// are bitcastable, and we can skip other stages, and go to contents
+ /// comparison.
+ /// Stage 3: Pointer types are greater than non-pointers. If both types are
+ /// pointers of the same address space - go to contents comparison.
+ /// Different address spaces: pointer with greater address space is
+ /// greater.
+ /// Stage 4: Types are neither vectors, nor pointers. And they differ.
+ /// We don't know how to bitcast them. So, we better don't do it,
+ /// and return types comparison result (so it determines the
+ /// relationship among constants we don't know how to bitcast).
+ ///
+ /// Just for clearance, let's see how the set of constants could look
+ /// on single dimension axis:
+ ///
+ /// [NFCT], [FCT, "others"], [FCT, pointers], [FCT, vectors]
+ /// Where: NFCT - Not a FirstClassType
+ /// FCT - FirstClassTyp:
+ ///
+ /// 2. Compare raw contents.
+ /// It ignores types on this stage and only compares bits from L and R.
+ /// Returns 0, if L and R has equivalent contents.
+ /// -1 or 1 if values are different.
+ /// Pretty trivial:
+ /// 2.1. If contents are numbers, compare numbers.
+ /// Ints with greater bitwidth are greater. Ints with same bitwidths
+ /// compared by their contents.
+ /// 2.2. "And so on". Just to avoid discrepancies with comments
+ /// perhaps it would be better to read the implementation itself.
+ /// 3. And again about overall picture. Let's look back at how the ordered set
+ /// of constants will look like:
+ /// [NFCT], [FCT, "others"], [FCT, pointers], [FCT, vectors]
+ ///
+ /// Now look, what could be inside [FCT, "others"], for example:
+ /// [FCT, "others"] =
+ /// [
+ /// [double 0.1], [double 1.23],
+ /// [i32 1], [i32 2],
+ /// { double 1.0 }, ; StructTyID, NumElements = 1
+ /// { i32 1 }, ; StructTyID, NumElements = 1
+ /// { double 1, i32 1 }, ; StructTyID, NumElements = 2
+ /// { i32 1, double 1 } ; StructTyID, NumElements = 2
+ /// ]
+ ///
+ /// Let's explain the order. Float numbers will be less than integers, just
+ /// because of cmpType terms: FloatTyID < IntegerTyID.
+ /// Floats (with same fltSemantics) are sorted according to their value.
+ /// Then you can see integers, and they are, like a floats,
+ /// could be easy sorted among each others.
+ /// The structures. Structures are grouped at the tail, again because of their
+ /// TypeID: StructTyID > IntegerTyID > FloatTyID.
+ /// Structures with greater number of elements are greater. Structures with
+ /// greater elements going first are greater.
+ /// The same logic with vectors, arrays and other possible complex types.
+ ///
+ /// Bitcastable constants.
+ /// Let's assume, that some constant, belongs to some group of
+ /// "so-called-equal" values with different types, and at the same time
+ /// belongs to another group of constants with equal types
+ /// and "really" equal values.
+ ///
+ /// Now, prove that this is impossible:
+ ///
+ /// If constant A with type TyA is bitcastable to B with type TyB, then:
+ /// 1. All constants with equal types to TyA, are bitcastable to B. Since
+ /// those should be vectors (if TyA is vector), pointers
+ /// (if TyA is pointer), or else (if TyA equal to TyB), those types should
+ /// be equal to TyB.
+ /// 2. All constants with non-equal, but bitcastable types to TyA, are
+ /// bitcastable to B.
+ /// Once again, just because we allow it to vectors and pointers only.
+ /// This statement could be expanded as below:
+ /// 2.1. All vectors with equal bitwidth to vector A, has equal bitwidth to
+ /// vector B, and thus bitcastable to B as well.
+ /// 2.2. All pointers of the same address space, no matter what they point to,
+ /// bitcastable. So if C is pointer, it could be bitcasted to A and to B.
+ /// So any constant equal or bitcastable to A is equal or bitcastable to B.
+ /// QED.
+ ///
+ /// In another words, for pointers and vectors, we ignore top-level type and
+ /// look at their particular properties (bit-width for vectors, and
+ /// address space for pointers).
+ /// If these properties are equal - compare their contents.
+ int cmpConstants(const Constant *L, const Constant *R);