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* [Bug middle-end/47661] New: predict is confused by FP comparisons when math can trap
@ 2011-02-09 12:31 rguenth at gcc dot gnu.org
2011-03-21 14:09 ` [Bug middle-end/47661] " rguenth at gcc dot gnu.org
2011-03-21 14:35 ` rguenth at gcc dot gnu.org
0 siblings, 2 replies; 3+ messages in thread
From: rguenth at gcc dot gnu.org @ 2011-02-09 12:31 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47661
Summary: predict is confused by FP comparisons when math can
trap
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: middle-end
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: rguenth@gcc.gnu.org
CC: hubicka@gcc.gnu.org, espindola@google.com
Without -fno-trapping-math we split away FP comparisons from the actual
conditional jump like
D.2683 = x < 0.0;
if (D.2683 != 0) goto <D.2684>; else goto <D.2685>;
this results in different prediction results for BB frequencies compared to
if (x < 0.0) goto <D.2683>; else goto <D.2684>;
which is odd (for C-ray this causes us to belive ray_sphere is more
costly time-wise with -ffast-math).
It is dubious that we use tree_could_trap_p in is_gimple_condexpr
instead of tree_could_throw_p (which would conditionalize the above
on -fnon-call-exceptions -fexceptions at least). 4.3 did neither,
tuples introduced that check with
2008-05-02 Rafael Espíndola <espindola@google.com>
* tree-gimple.c (is_gimple_condexpr): Do not allow
trapping comparisons.
* tree-eh.c (tree_could_trap_p): Fix handling of floating
point comparisons.
Still the prediction will be off with exceptions turned on.
I can't see any reason why
Index: gimple.c
===================================================================
--- gimple.c (revision 169963)
+++ gimple.c (working copy)
@@ -2581,7 +2581,7 @@ bool
is_gimple_condexpr (tree t)
{
return (is_gimple_val (t) || (COMPARISON_CLASS_P (t)
- && !tree_could_trap_p (t)
+ && !tree_could_throw_p (t)
&& is_gimple_val (TREE_OPERAND (t, 0))
&& is_gimple_val (TREE_OPERAND (t, 1))));
}
would be incorrect. Rafael, do you remember anything about the reasoning
to use tree_could_trap_p instead of tree_could_throw_p?
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug middle-end/47661] predict is confused by FP comparisons when math can trap
2011-02-09 12:31 [Bug middle-end/47661] New: predict is confused by FP comparisons when math can trap rguenth at gcc dot gnu.org
@ 2011-03-21 14:09 ` rguenth at gcc dot gnu.org
2011-03-21 14:35 ` rguenth at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: rguenth at gcc dot gnu.org @ 2011-03-21 14:09 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47661
--- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-03-21 13:50:35 UTC ---
Author: rguenth
Date: Mon Mar 21 13:50:26 2011
New Revision: 171236
URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=171236
Log:
2011-03-21 Richard Guenther <rguenther@suse.de>
PR middle-end/47661
* gimple.c (is_gimple_condexpr): Use tree_could_throw_p.
Modified:
trunk/gcc/ChangeLog
trunk/gcc/gimple.c
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug middle-end/47661] predict is confused by FP comparisons when math can trap
2011-02-09 12:31 [Bug middle-end/47661] New: predict is confused by FP comparisons when math can trap rguenth at gcc dot gnu.org
2011-03-21 14:09 ` [Bug middle-end/47661] " rguenth at gcc dot gnu.org
@ 2011-03-21 14:35 ` rguenth at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: rguenth at gcc dot gnu.org @ 2011-03-21 14:35 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47661
Richard Guenther <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2011.03.21 13:51:31
Ever Confirmed|0 |1
--- Comment #2 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-03-21 13:51:31 UTC ---
predict confusion about
pred = a CMP b;
if (pred)
remains.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2011-02-09 12:31 [Bug middle-end/47661] New: predict is confused by FP comparisons when math can trap rguenth at gcc dot gnu.org
2011-03-21 14:09 ` [Bug middle-end/47661] " rguenth at gcc dot gnu.org
2011-03-21 14:35 ` rguenth at gcc dot gnu.org
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