https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80432
--- Comment #3 from Hao Zhang <theivorytower at gmail dot com> --- (In reply to Hao Zhang from comment #2) > (In reply to Martin Liška from comment #1) > > Can't reproduce, can you please provide options you use to build the > > executable? > > I didn't use any extra options besides g++ pow.cpp, and both my CFLAGS and > CXXFLAGS environment variables are empty. And I just found out moments ago > compiling with -O1 gives the right result while compiling with -O0 gives the > wrong result. I also tried to turn on each of the 42 optimizations provided > by -O1 individually, and I found none of the 42 optimizations ALONE can get > rid of the problem. So there must be some combinations of optimizations that > can get rid of the problem. > > My glibc version is 2.25 and kernel version is 4.10.9. And I have reproduced > the error on two different computers. Is there any other information I can > provide to help pinpoint the problem? Thanks! I also found out that g++ -O1 pow.cpp gives the expected results, while the following command gives the wrong results: g++ -fauto-inc-dec -fbranch-count-reg -fcombine-stack-adjustments -fcompare-elim -fcprop-registers -fdce -fdefer-pop -fdelayed-branch -fdse -fforward-propagate -fguess-branch-probability -fif-conversion2 -fif-conversion -finline-functions-called-once -fipa-pure-const -fipa-profile -fipa-reference -fmerge-constants -fmove-loop-invariants -freorder-blocks -fshrink-wrap -fshrink-wrap-separate -fsplit-wide-types -fssa-backprop -fssa-phiopt -ftree-bit-ccp -ftree-ccp -ftree-ch -ftree-coalesce-vars -ftree-copy-prop -ftree-dce -ftree-dominator-opts -ftree-dse -ftree-forwprop -ftree-fre -ftree-phiprop -ftree-sink -ftree-slsr -ftree-sra -ftree-pta -ftree-ter -funit-at-a-time -fomit-frame-pointer pow.cpp This is weird, isn't the two forms of command equivalent?
