[Bug tree-optimization/32390] tree-ssa-math-opts.c performs too many IL scans
--- Comment #8 from rguenth at gcc dot gnu dot org 2009-02-06 22:51 --- Sure. There's this other problem of testsuite regressions you'll get. I've been there, it takes a _lot_ of time to do even minimal pass re-ordering / removing :( The best strathegy was always to fix deficiencies in passes to not need followup ones or iterating. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32390
[Bug tree-optimization/32390] tree-ssa-math-opts.c performs too many IL scans
--- Comment #7 from steven at gcc dot gnu dot org 2009-02-06 22:43 --- Then they should be grouped. And kept grouped. Here's one case where there has to be a trade-off between micro-optimizations for specific cases, and compile time for everyone. Please, for once, let us seriously consider this trade-off. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32390
[Bug tree-optimization/32390] tree-ssa-math-opts.c performs too many IL scans
--- Comment #6 from rguenth at gcc dot gnu dot org 2009-02-06 22:29 --- Only they all run at different times during the pass pipeline ;) -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32390
[Bug tree-optimization/32390] tree-ssa-math-opts.c performs too many IL scans
--- Comment #5 from steven at gcc dot gnu dot org 2009-02-06 21:41 --- We have a new candidate: bswap optimization. Diego's idea to do "a single scan that calls back to all these transformations on every statement" really still sounds like The Right Thing to do. -- steven at gcc dot gnu dot org changed: What|Removed |Added Status|UNCONFIRMED |NEW Ever Confirmed|0 |1 Keywords||compile-time-hog Last reconfirmed|-00-00 00:00:00 |2009-02-06 21:41:34 date|| http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32390
[Bug tree-optimization/32390] tree-ssa-math-opts.c performs too many IL scans
--- Comment #4 from paolo dot bonzini at lu dot unisi dot ch 2007-06-19 05:09 --- Subject: Re: tree-ssa-math-opts.c performs too many IL scans > We have reciprocal pass (in fact CSE recip pass) that CSEs 1.0/z from x/z, > y/z, > .../z. This is done by scanning function for RDIV_EXPR, where denominator (z) > is the same. If 1.0/func() -> rfunc() conversion is done before recip pass, we > loose the ability to scan for RDIV_EXPRs and the ability to CSE the division. You could still use a pointer_set or pointer_map to save where the RDIV_EXPRs are and avoid scanning the IL twice. Paolo -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32390
[Bug tree-optimization/32390] tree-ssa-math-opts.c performs too many IL scans
--- Comment #3 from ubizjak at gmail dot com 2007-06-18 17:40 --- (In reply to comment #2) > We need a better explanation than this. Uros agreed to summarize the > IRC discussion to close this issue. It'd be useful if we keep that same > discussion on the source code itself. The need for separate IL passes could be explained by: We have reciprocal pass (in fact CSE recip pass) that CSEs 1.0/z from x/z, y/z, .../z. This is done by scanning function for RDIV_EXPR, where denominator (z) is the same. If 1.0/func() -> rfunc() conversion is done before recip pass, we loose the ability to scan for RDIV_EXPRs and the ability to CSE the division. By putting 1.0/func()->rfunc() after recip pass, we simply run another scan for RDIV_EXPRs with function as their argument. Note that we already CSE'd 1.0/func(), so the conversion into rfunc() is trivial. This is the reason why function recip pass needs to run after recip (aka CSE recip) pass. Next convesion is sqrt(a/b) -> rsqrt(b/a) conversion that runs after rfunc recip pass as a separate pass (so, in the function granulartiy). If this pass is run together or before rfunc pass, then rsqrt pass would convert expressions like 1.0/sqrt(a/b) into 1.0/rsqrt(b/a). There is no point for rfunc pass (that would follow) to convert this to sqrt(b/a). -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32390
[Bug tree-optimization/32390] tree-ssa-math-opts.c performs too many IL scans
--- Comment #2 from dnovillo at google dot com 2007-06-18 14:00 --- Subject: Re: tree-ssa-math-opts.c performs too many IL scans On 6/18/07 9:56 AM, rguenth at gcc dot gnu dot org wrote: > --- Comment #1 from rguenth at gcc dot gnu dot org 2007-06-18 13:56 > --- > All three transformations are done at different stages of the optimization > pipeline due to various reasons. We need a better explanation than this. Uros agreed to summarize the IRC discussion to close this issue. It'd be useful if we keep that same discussion on the source code itself. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32390
[Bug tree-optimization/32390] tree-ssa-math-opts.c performs too many IL scans
--- Comment #1 from rguenth at gcc dot gnu dot org 2007-06-18 13:56 --- All three transformations are done at different stages of the optimization pipeline due to various reasons. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32390
