> While we could add some hash_table/bitmap or whatever other data structure > to track registers we've already looked at, having unbounded look through > register copies looks dangerous to me for compile time complexity in > pathological cases, and while on certain architectures I could understand > very deep chains of say reg2 = reg1 + constant; reg3 = reg2 + constant; ... > (or with post-increment/decrement/modify) if the target addressing mode > doesn't allow suitable immediates in addresses, having chains of simple > reg2 = reg1; reg3 = reg2; reg4 = reg3; reg5 = reg4; ... > chains with thousands copies will unlikely appear and would unlikely result > in something useful for the loop iv optimization, so this patch instead > just looks through at most 128 copies (I don't think we need a param for > that). > > Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? > > 2020-01-03 Jakub Jelinek <ja...@redhat.com> > > PR rtl-optimization/93088 > * loop-iv.c (find_single_def_src): Punt after looking through > 128 reg copies for regs with single definitions. Move definitions > to first uses. > > * gcc.target/i386/pr93088.c: New test.
OK with me, thanks. -- Eric Botcazou
