On 06/26/2015 03:24 AM, Richard Biener wrote:
On Thu, 25 Jun 2015, Richard Biener wrote:
This moves fold_sign_changed_comparison. Shows up in gcc.dg/pr55833.c
I'll eventually massage it according to Jakubs suggestion to do a
#ifndef HAVE_canonicalize_funcptr_for_compare
#define HAVE_canonicalize_funcptr_for_compare 0
#endif
somewhere (defaults.h should work I guess).
Bootstrap and regtest running on x86_64-unknown-linux-gnu.
This runs into
Running target unix//-m32
FAIL: g++.dg/tree-ssa/calloc.C -std=gnu++11 scan-tree-dump-not optimized
"malloc"
where we now optimize
n_5 = (size_t) n_4(D);
...
<bb 5>:
- if (n_5 != 0)
+ if (n_4(D) != 0)
but both VRP and DOM fail to record equivalences for n_5 from
the updated condition (I have a patch to fix VRP but not DOM).
So you want an equivalence recorded for n_5, even though it no longer
appears in the conditional (but presumably has other uses)?
DOM has some code for this already, but it's kind-of backwards from what
you're trying to do in terms of when it's used. That code might be
factorable and usable elsewhere in DOM.
I think we're simply missing a pass that can "properly" deal
with this kind of stuff. For example DOM could re-visit
stmts which have uses of SSA names we added temporary
equivalences for (ones that dominate the current block,
others we'll (re-)visit anyway). That would fix this testcase
but to catch secondary effects you'd need to re-visit uses of
the defs of the revisited stmts as well (if anything interesting
was produced, of course).
This problem feels a bit like it's better handled by an optimizer
independent of DOM. Probably a backwards IL walking context sensitive
optimizer. I want to do something like that for threading, but haven't
much pondered other use cases for that kind of structure.
If you could create a BZ and include the patches you're playing with and
a reference to the failing test (calloc.C for -m32), it'd be appreciated.
Jeff
