> -----Original Message----- > From: Jeffrey Law <[email protected]> > Sent: Thursday, August 6, 2026 11:18 AM > To: Liu, Hongtao <[email protected]>; [email protected]; Rachit > Mehta <[email protected]> > Cc: [email protected] > Subject: Re: [PATCH 1/2] tree-scalar-evolution: Handle idempotent > recurrences [PR124460] > > > > On 8/4/2026 8:45 PM, liuhongt wrote: > > SCEV does not represent recurrences such as repeated MIN_EXPR or > > BIT_AND_EXPR updates. Recognize MIN_EXPR, MAX_EXPR, BIT_AND_EXPR, > > BIT_IOR_EXPR and ABS_EXPR updates with a loop-invariant second > operand. > > After any positive number of iterations their value is the operation > > applied once to the initial value. > > > > gcc/ChangeLog: > > > > PR middle-end/124460 > > * tree-scalar-evolution.cc (loop_phi_for_update): New function. > > (build_loop_update): Likewise. > > (compute_idempotent_loop_value): Likewise. > > (final_value_replacement_loop): Use it. > So there are pieces of both implementations that I prefer :-) > > Rachit's patch is better at checking for a variety of potential worries. > Just some > examples it verifies that the loop runs at least one time, avoiding problems > with SSA_NAME_OCCURS_IN_ABNORMAL_PHI, etc. > > This patch is better in that it handles more types of operations. > > So what I'd suggest is we extend Rachit's implementation to cover min, max, > abs, and, ior.
Sound ok to me. > > Rachit, are you willing to do that work? I would suggest y'all be co-authors > on > the result. > > Thanks, > Jeff
