https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91965
--- Comment #3 from Alexander Monakov <amonakov at gcc dot gnu.org> --- (In reply to Marc Glisse from comment #2) > What exact transformation do you want? Canonicalize the constant C to > something like C % (1 << (bitsize - N))? I'm thinking (C << N) >>> N where '>>>' is sign-extending right shift. In other words, duplicate the bit at position (bitsize - 1 - N) to the left. In the opening example, I want to go from (0xfffff - a) << 44 to (-1 - a) << 44 > For unsigned only... didn't we use to canonicalize in the reverse direction, > i.e. from x*4 to x<<2? For unsigned - because we promise not to use undefined overflow for signed left shifts? Can we canonicalize to a wrapping multiplication?
