Changed compareInstSpecificProperies() methods to protected and added comparision of elemnet types of pointers in compareTypes()

Quoting the observed text segment sizes for few object files in MySQL, by enabling MergeFunctions by default and comparing them with baseline.

Ran the llvm test-suite. All the tests were going fine.

Changed name from haveSameSpecialState() to compareSpecialState()

Changed named of comparator method in each subclass to compareInstSpecificProperties()

Comment added

Changed hasSamePropertiesAs() method in each subclass of IR to introduce total ordering between two instructions of that subclass
and modified FunctionComparator to use haveSameSpecialState() method for IR comparision.

In D82892#2151162, @tejohnson wrote:

Why not just make hasSamePropertiesAs a pure virtual on Instruction, then you don't need any switch statement in haveSameSpecialState? You'd need to do the cast on the Instruction operand within the implementations, but that would be cleaner IMO. For the ones that currently return true, you wouldn't need the cast just an opcode comparison.

@jfb @tejohnson, just reminding you of the review as the patch has been lying dormant since a week.

Comment added

In D82892#2133157, @tejohnson wrote:

Is this a bug fix? If it is NFC (No Functional Change) please specify that in the title, otherwise needs a test case.

Added hasSamePropertiesAs() method in each subclass of the IR which should say how two IR instructions of that subclass should be compared.
Changed haveSameSpecialState() method to make use of the hasSamePropertiesAs() methods.
When there is a change to IR, only the hasSamePropertiesAs() method needs of that subclass need to be updated.

Added case for Freeze instruction.

Added comparision for all types in haveSameSpecialState() of Instruction.cpp and changed the if-else branching to switch over the Instruction Opcode

In D82892#2123584, @nikic wrote:

At this point, I would recommend writing this as a switch over the instruction opcode.

@vish99 will your work in https://reviews.llvm.org/D82892 check alignment changes as well?

Changes to merge the 5 patches together

Changes to the merge the 5 patches together

Changes to merge the 5 patches together

Reverting back to diff 222348, the previous diff was against a wrong branch

Changes to sync D52898 with D52966