-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 10/06/11 09:37, Jakub Jelinek wrote: > On Thu, Oct 06, 2011 at 05:28:36PM +0200, Kai Tietz wrote: >> None. I had this implemented first. But Richard was concerned >> about making non-IF conditions too long. I understand that >> point that it might not that good to always modify >> unconditionally to AND/OR chain. For example >> >> if (a1 && a2 && a3 && .... && a100) return 1; >> >> would be packed by this patch into 50 branches. If we would >> modify all of them into AND, then we would calculate for all 100 >> values the result, even if the first a1 is zero. This doesn't >> improve speed pretty well. >> >> But you are right, that from the point of reassociation >> optimization it could be in some cases more profitable to have >> packed all elements into on AND-chain. > > Yeah. Perhaps we should break them up after reassoc2, or on the > other side teach reassoc (or some other pass) to be able to do the > optimizations on a series of GIMPLE_COND with no side-effects in > between. See e.g. PR46309, return a == 3 || a == 1 || a == 2 || a > == 4; isn't optimized into (a - 1U) < 4U, although it could, if > branch cost cause it to be broken up into several GIMPLE_COND > stmts. Or if user writes: if (a == 3) return 1; if (a == 1) return > 1; if (a == 2) return 1; if (a == 4) return 1; return 0; (more > probably using enums). I haven't followed this thread as closely as perhaps I should; what I'm seeing discussed now looks a lot like condition merging and I'm pretty sure there's some research in this area that might guide us. multi-variable condition merging is the term the authors used.
jeff -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iQEcBAEBAgAGBQJOjeYFAAoJEBRtltQi2kC7eFMIALjFM/GIg1DDryU59EoFQe5A x7pvx3FSlcjLWeyIlzYJvWF4wGybRNNXp5qziIedO6qp0Z/06VvCU07A10VoWSig /EFufo5l+Jef5s1d0mA6mBJ9A52HDL2ipOK8YDQbVzJWqHdaXLrrzUni3wGwcUVs v3UIi5OevjRhJ55fRVxBcReJKF6YAzxFDxqOnVGAbf9R3BEJ2T9JW2CLhIcd/T1L D9K+6YymHaN9eYh7B7gPKG88q+5JjcStHuMQODKSAegt3T4iP9CH/G5dV8u95Y+q 6mxo8gOGAwYR7N/U6fuXRaGJEzWSdrqRy2EBF5B7+Rt6lSWXdfzUEBusT24i67A= =HIrU -----END PGP SIGNATURE-----
