Hello, I have a piece of floating point EFT arithmetic in my code, but I get a rather strange code generation for it. Here's the actual source code and flags I've experimented with: https://godbolt.org/z/oJEs4U The first pane is what I expect to get as output, that is, all the arithmetic operations in the assembly. However the strange thing is I have to compile with -funsafe-math-optimizations to actually produce that. The second pane is the same thing but with -fno-unsafe-math-optimizations (default) and surprisingly the optimizer strips the relevant instructions. I would've thought the -fno-associative-math enough to prevent that from happening but for some reason it's not. The third pane I added for good measure. It illustrates the same flags as the first one (the one that generates the correct assembly), but the flags are applied through an attribute directly to the symbol. Even more surprisingly this generates yet another completely different piece of output, which doesn't even seem to do what's supposed to (unsafe means unsafe in this case, I gather). Has anyone any insight into this? Why isn't -fno-associative-math enough in stopping the optimizer here? Why would -funsafe-math-optimizations actually trigger the correct code being generated? And as a curiosity, why would it matter if the flag is applied to the symbol in contrast to the pragma? Thanks in advance! Konstantin.
