https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105930
--- Comment #12 from Linus Torvalds <torva...@linux-foundation.org> --- (In reply to Jakub Jelinek from comment #11) > Anyway, I think we need to understand what makes it spill that much more, > and unfortunately the testcase is too large to find that out easily, I think > we should investigate commenting out some rounds. I think you can comment out all the rounds except for one, and still see the effects of this. At least when I try it on godbolt with just ROUND(0) in place and rounds 1-12 deleted, for gcc-11.3 I get a stack frame of 388. And with gcc-12.1 I get a stack frame of 516. Obviously that's not nearly as huge, but it's still a fairly significant expansion and is presumably due to the same basic issue. I used godbolt just because I no longer have 11.3 installed to compare against, so it was the easiest way to verify that the stack expansion is still there. Just to clarify: that's still with -O2 -m32 -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx I'm sure it depends on the flags. The code is still not exactly trivial with just one round in place. It's a cryptographic hash, after all. But when compiling for 64-bit mode it all looks fairly straightforward, it really is that DImode stuff that makes it really ungainly when using -m32.
