Am Fri, 21 Jul 2017 23:44:53 +0000 schrieb Mike <n...@none.com>: > My stm32 demo has now been updated and working with GDC/GCC > 7.1.0. Thanks for all your improvements. > > However, I'm getting broken binaries with -O2 and -O3. I've > nailed the culprit down to -fschedule-insns (i.e. if I add > -fno-schedule-insns to -O2 or -O3, the binary works fine). > > I disassembled '-O2' and '-O2 -fno-schedule-insns' and compared > them, but they were quite different all the way through. No only > because of address locations, but also different registers and > even different opcodes. (e.g. 'str r2, [sp, #12]' vs 'strd r1, > r2, [sp, #8]')
This can unfortunately happen if scheduling allows further optimizations. Then the generated code might look nothing like the original code. It's also possible that this is only caused by a combination of optimization passes, I guess it doesn't happen using -fschedule-insns without other -O flags? > > Is there anything I can do to provide more actionable information > to help identify the underlying cause? As I don't have an ARM bare metal compiler ready to test: The output of -fdump-tree-all and -fdump-rtl-all would be useful. The tree output is usually quite readable, rtl not so much... There might be some more useful switches on https://gcc.gnu.org/onlinedocs/gcc/Developer-Options.html -- Johannes
