I'd also be curious to discover how many distinct x86 instructions gcc can even emit? I expect the answer is "a lot less than all of them."
Of course, that’s not an interesting observation.
It gets (somewhat) interesting when you realize that one may inadvertently include in-line assembly. Do you call including system headers that happen to contain inline assembly cheating? Including headers for a standard C library? Compiling with old-fashioned compiler flags (for example to generate FPU instructions for the x87)?
$ objdump -w -j .text --no-show-raw-insn -d /usr/bin/emacs-gtk | egrep '^ *[0-9]+:' | awk '{print $2}' | sort | uniq | wc -l
130
$ objdump -w -j .text --no-show-raw-insn -d /bin/ls | egrep '^ *[0-9]+:' | awk '{print $2}' | sort | uniq | wc -l
97
$ objdump -w -j .text --no-show-raw-insn -d firefox-bin | egrep '^ *[0-9]+:' | awk '{print $2}' | sort | uniq | wc -l
136I wonder if the numbers would change significantly for gentoo or anything compiled manually that had more knowledge of the CPU specifics?
$ objdump -w -j .text --no-show-raw-insn -d /usr/lib64/firefox/firefox-bin | egrep '^ \*[0-9]+:' | awk '{print $2}' | sort | uniq | wc -l
134