On 2018-09-04 19:02:02 -0400, Tom Lane wrote: > Andres Freund <and...@anarazel.de> writes: > > ... Note that we've previously encountered similar issues > > on gcc, which is why we've tried to force gcc's hand with > > -fexcess-precision=standard. > > Right. Annoying that clang doesn't have that. We can't realistically > program around an issue that might or might not show up depending on the > whims of the compiler's register allocation.
Right. > > I kinda wonder if we should add -mno-x87 or such in configure when we > > detect clang, obviously it doesn't deal correctly with this. > > Seems worth looking into, but what happens if someone tries to compile > for x87 hardware? Or do we care anymore? It generates linker errors: clang-8 -std=gnu99 -march=i386 -O2 -m32 -mno-x87 ~/tmp/flttst.c -o ~/tmp/flttst && ~/tmp/flttst /usr/bin/ld: /tmp/flttst-ba93f5.o: in function `main': flttst.c:(.text+0x37): undefined reference to `__muldf3' /usr/bin/ld: flttst.c:(.text+0x67): undefined reference to `__gedf2' clang: error: linker command failed with exit code 1 (use -v to see invocation) I think we only should add the flag when detecting clang, so a user with just a < pentium-4 could resort to gcc. Although honestly, I don't think that's really something usefully to cater for. The one hangup I have with this is that clang on *bsd defaults to i486 (and thus x87) when compiling 32bit binaries. That's obviously *terrible* for performance, but it'd still be annoying for some users. While I don't immediately know how, that seems like an argument for doing this in configure, and suggesting a better compiler flag. Greetings, Andres Freund
