https://gcc.gnu.org/bugzilla/show_bug.cgi?id=24021
Aldy Hernandez <aldyh at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jeffreyalaw at gmail dot com,
| |richard.guenther at gmail dot
com
--- Comment #6 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
Preview of what's to come.
Implementing a bare bones frange class and associated relational operators in
range-ops we can get:
void link_error();
void func();
int foo(float f)
{
if (f > 3.0)
{
func();
if (f < 2.0)
link_error();
}
}
Folding statement: if (f_2(D) > 3.0e+0)
Not folded
Folding statement: func ();
Not folded
Folding statement: if (f_2(D) < 2.0e+0)
Folding predicate f_2(D) < 2.0e+0 to 0
Folded into: if (0 != 0)
And we can also get symbolics:
int bar(float f, float g)
{
if (f > g)
{
func();
if (f < g)
link_error();
}
}
Folding statement: if (f_2(D) < g_3(D))
folding with relation f_2(D) > g_3(D)
Folding predicate f_2(D) < g_3(D) to 0
Folded into: if (0 != 0)
My proof of concept has ranger dumps looking like:
=========== BB 2 ============
Imports: f_2(D)
Exports: f_2(D)
f_2(D) float VARYING
<bb 2> :
if (f_2(D) > 3.0e+0)
goto <bb 3>; [INV]
else
goto <bb 5>; [INV]
2->3 (T) f_2(D) : float (3.0e+0, +Inf]
2->5 (F) f_2(D) : float [-Inf, 3.0e+0]
Interestingly, since the threader uses ranger, I had to turn off the threader
for the above snippets, because ethread gets the first one before evrp even
gets a whack at it:
[1] Registering jump thread: (2, 3) incoming edge; (3, 5) nocopy;
path: 2->3->5 SUCCESS
Removing basic block 3
;; basic block 3, loop depth 0
;; pred:
func ();
if (f_2(D) < 2.0e+0)
goto <bb 4>; [INV]
else
goto <bb 5>; [INV]
;; succ: 4
;; 5
As I've mentioned, I'm hoping some floating expert can take this across to goal
line, as my head will start spinning as soon as we start talking about NANs and
such. The range-op work will likely require floating specialized knowledge.
