On 12 August 2015 at 10:22, Jonathan Wakely wrote: > On 12 August 2015 at 00:03, Jeffrey Walton wrote: >> >> *If* I force -fPIC on the command line and endure 135 or so of these: >> >> $ make >> g++ -DNDEBUG -g -O3 -fPIC -march=native -pipe -c shacal2.cpp >> shacal2.cpp:1:0: warning: -fPIC ignored for target (all code is >> position independent) >> // shacal2.cpp - by Kevin Springle, 2003 >> ^ >> >> Then the program executes fine. But its a very messy compile, and its >> probably not going to be worth forcing -fPIC because we will get too >> much negative feedback. > > This doesn't make any sense. If -fPIC is ignored then how does addng > it make any difference? > > Have you compared the object files with and without -fPIC to see if it > does make any difference? If it does, there shouldn't be a warning > about ignoring it. Looking at the code for Cysgin it looks like for 64-bit -fpic is always used, so if you use -fPIC you get a warning, but -fpic would not get a warning. Adding -fPIC should not affect codegen, because with or without it you get -fpic. For 32-bit adding either -fpic or -fPIC gives a warning, but should not affect codegen. I tested it with mingw32 (which shares the relevant code with Cygwin) and see no difference in codegen with or without -fPIC. So are you absolutely sure that adding -fPIC makes a difference, and there isn't some other change in options between the two builds?
