__attribute__ optimize, specifying multiple flags, and failing code at different -O levels

Question

I have some code that is being compiled with GCC for a micro. I noticed that when compiling the debug build, the system works just fine. But when I compile the release build, the system does not boot up.

After working on the issue for awhile, I narrowed down the problem to one function where if I specify a lesser optimization level (-O0 instead of -Os), the system will boot up just fine in the release build. So there is presumably a flag that -Os sets that is causing the code in that particular function to not work.

I had planned to track down the underlying issue by taking all the flags that -Os sets, and finding the one that causes the system not to boot.

I was trying to do the following:

__attribute__ ((optimize("-fauto-inc-dec", "-fcompare-elim", "-fcprop-registers", "-fdce", "-fdefer-pop", "-fdelayed-branch", "-fdse", "-fguess-branch-probability", "-fif-conversion2", "-fif-conversion", "-fipa-pure-const", "-fipa-profile", "-fipa-reference", "-fmerge-constants", "-fsplit-wide-types", "-ftree-bit-ccp", "-ftree-builtin-call-dce", "-ftree-ccp", "-ftree-ch", "-ftree-copyrename", "-ftree-dce", "-ftree-dominator-opts", "-ftree-dse", "-ftree-forwprop", "-ftree-fre", "-ftree-phiprop", "-ftree-sra", "-ftree-pta", "-ftree-ter", "-funit-at-a-time")))

and then eliminate flags until the system would boot. The problem is, is that I kept narrowing it down and narrowing it down, until I discovered that I can't get even set a single flag and get the system to boot.

So now I'm thinking that I'm doing something wrong with the way that I'm setting the optimization. If I put in a superfluous non-existent flag somewhere in the middle of those flags, like -fiam-fake-flag, the compiler detects it and spits out an error (which at first made me feel like I was setting these flags correctly).

I don't want to use pragma, because:

" Each function that is defined after this point is as if attribute((optimize("STRING"))) was specified for that function. "

and I only want the optimization on this one function so I can narrow down the problem.

So, am I setting these flags incorrectly? Is there a better way to specify a whole bunch of compiler flags for only 1 specific function?

If it weren't going on a micro, I could just specify all the flags I want in the Makefile and apply it to all functions, but doing so makes the program too big to fit on the micro.

Answer 1

Is your flag declared as volatile? Try posting the problematic function. – egur

that is TOTALLY what it was. Thank you, egur. – Mike Gibson