Get Assembly code after every optimization GCC makes?

Question

From Optimization Compiler on Wikipedia,

Compiler optimization is generally implemented using a sequence of optimizing transformations, algorithms which take a program and transform it to produce a semantically equivalent output program that uses fewer resources.

and GCC has a lot of optimization options.

I'd like to study the generated assembly (the one -S gives) after each optimization GCC performs when compiling with different flags like -O1, -O2, -O3, etc.

How can I do this?

Edit: My input will be C code.

Answer 1

gcc -S (Capital S)

gives asm output, but the assembler can change things so I prefer to just make an object

gcc -c -o myfile.o myfile.c

then disassemble

objdump -D myfile.o

Understand that this is not linked so external branch destinations and other external addresses will have a placeholder instead of a real number. If you want to see the optimizations compile with no optimizations (-O0) then compile with -O1 then -O2 and -O3 and see what if anything changes. There are other optimzation flags as well you can play with. To see the difference you need to compile with and without the flags and compare the differences yourself.

diff won't work, you will see why (register allocation changes).