------- Comment #6 from zippel at gcc dot gnu dot org 2007-07-09 15:27 ------- (In reply to comment #5) > as you suggest creates worse assembly (look at the extra shift) > > foo: > pushl %ebp > movl %esp, %ebp > movl 12(%ebp), %ecx > movl 8(%ebp), %edx > popl %ebp > sall $2, %ecx > movl 8(%ecx,%edx), %eax > addl 4(%ecx,%edx), %eax > addl 12(%ecx,%edx), %eax > ret
The cost of this is dependent on the target, so IMO the shift could be propagated back into the address at RTL level. > so there is no form that is clearly better to canonicalize to. Your example is rather artificial and depends on that (i + x) * y is completely eliminated. My main point is still that such expression are far more difficult to translate into proper address operations. To generate addresses targeting a form of (i * x) + y is clearly better. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32698
