I know ASM is generaly run through an assembler and result in a more or less one to one mapping to the final binary but that's not what I'm thinking of.
Does anyone make a tool that treats ASM (or object files) as a complied language that it can perform the full gamut of optimizations on? While such a tool might not be particularly useful in and of it's self, it could do things like function inlining from closed source static libraries.
while I agree with travelboy's answer in that any such 'compiled assembly' language wouldn't be assembly anymore, I have to mention that there are 'recompilers', and JITs whose source language is machine language (not even assembly).
These programs take a bunch of executable code, typically already loaded and ready to execute, and transform it, recognizing a varyiety of constructs and replacing with different versions, which can be better, faster, safer or just different.
qemu is an example of this. In it's original form is a CPU emulator that works by recompiling from a given CPU binary into a different CPU for execution (Binary Translation). But it can also work when both CPUs are the same, in this case the transformation allows privileged code to execute in a VM environment by 'breaking out' to the hardware emulator.
A very interesting example is HP Dynamo (old Ars Technica article), a research software that achieved unexpected speedups by recompiling HP PA-8000 binaries.