[Bug tree-optimization/94893] Sign function not getting optimized to simple compare
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94893 --- Comment #5 from Andrew Pinski --- (In reply to Andrew Pinski from comment #4) > As for the original issue: > x.0_5 = (unsigned int) x_2(D); > _6 = -x.0_5; > _7 = _6 >> 31; > _8 = (int) _7; > > We have a pattern for basically this: > /* Fold (-x >> C) into -(x > 0) where C = precision(type) - 1. */ > > But only for !TYPE_UNSIGNED here. we can do it for unsigned where we just > get x > 0 instead. I have a patch which gets us to: # RANGE [irange] int [-1, 0] _3 = x_2(D) >> 31; _5 = x_2(D) > 0; # RANGE [irange] int [0, 1] MASK 0x1 VALUE 0x0 _6 = (intD.9) _5; # RANGE [irange] int [-1, 1] _7 = _3 | _6; _4 = _7 != 1; (_3 | _6) != 1 means !((_3 == 0) && (_6 == 1)) since _3 can't be 1 at all. (_3 == 0) is x >= 0 and _6 == 1 is `x > 0` and that combines to be just `x >= 0` . I think the above only works if the two ranges in the _3|_6 is [-1,0] and [1,0] . (_3 | _6) == -1 just means _3 == -1 even which we don't handle either (and would be simplier to handle than other cases).
[Bug tree-optimization/94893] Sign function not getting optimized to simple compare
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94893
Andrew Pinski changed:
What|Removed |Added
Assignee|unassigned at gcc dot gnu.org |pinskia at gcc dot
gnu.org
Status|NEW |ASSIGNED
--- Comment #4 from Andrew Pinski ---
(In reply to Andrew Pinski from comment #3)
> Note we also don't optimize:
>
> inline int sign1(int x)
> {
> return (x < 0 ? -1 : 0) | (x > 0 ? 1 : 0);
> }
> bool f1(int x)
> {
> return sign1(x) < 1;
> }
>
> To be just `x <= 0`
That is because forwprop leaves assignments that are not used anywhere still.
after dce7:
```
if (x_2(D) < 0)
goto ; [41.00%]
else
goto ; [59.00%]
[local count: 633507680]:
_7 = x_2(D) != 0;
_8 = (int) _7;
_5 = _8 ^ 1;
_10 = (bool) _5;
[local count: 1073741824]:
# prephitmp_11 = PHI <1(2), _10(3)>
```
After frowprop4:
```
if (x_2(D) < 0)
goto ; [41.00%]
else
goto ; [59.00%]
[local count: 633507680]:
_7 = x_2(D) != 0;
_8 = (int) _7;
_3 = x_2(D) == 0;
_5 = (int) _3;
[local count: 1073741824]:
# prephitmp_11 = PHI <1(2), _3(3)>
```
If those statements were removed then phiopt4 would be able to optimize
prephitmp_11 to: `(x_2(D) < 0) | (x_2(D) == 0)` which simplifies to `x_2(D) <=
0` .
Let me look into the forwprop issue here.
As for the original issue:
x.0_5 = (unsigned int) x_2(D);
_6 = -x.0_5;
_7 = _6 >> 31;
_8 = (int) _7;
We have a pattern for basically this:
/* Fold (-x >> C) into -(x > 0) where C = precision(type) - 1. */
But only for !TYPE_UNSIGNED here. we can do it for unsigned where we just get x
> 0 instead.
[Bug tree-optimization/94893] Sign function not getting optimized to simple compare
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94893
--- Comment #3 from Andrew Pinski ---
Note we also don't optimize:
inline int sign1(int x)
{
return (x < 0 ? -1 : 0) | (x > 0 ? 1 : 0);
}
bool f1(int x)
{
return sign1(x) < 1;
}
To be just `x <= 0`
[Bug tree-optimization/94893] Sign function not getting optimized to simple compare
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94893
Andrew Pinski changed:
What|Removed |Added
Ever confirmed|0 |1
Last reconfirmed||2021-04-26
Status|UNCONFIRMED |NEW
--- Comment #2 from Andrew Pinski ---
Confirmed.
Note the original code does have one slight undefined case, when x is INT_MIN
but that can be fixed by casting to unsigned before doing the negate of x.
That is:
inline int sign(int x)
{
return (x >> 31) | (-(unsigned)x >> 31);
}
CUT
Matching this:
_1 = x_5(D) >> 31;
x.0_2 = (unsigned int) x_5(D);
_3 = -x.0_2;
_4 = _3 >> 31;
_8 = (int) _4;
_6 = _1 | _8;
Into:
t = (int)(x > 0);
result = x < 0 ? - 1 : t;
Might not be the best thing.
[Bug tree-optimization/94893] Sign function not getting optimized to simple compare
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94893 Andrew Pinski changed: What|Removed |Added Severity|normal |enhancement
[Bug tree-optimization/94893] Sign function not getting optimized to simple compare
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94893 Gabriel Ravier changed: What|Removed |Added Target|x86_64-*-* | Blocks||19987 --- Comment #1 from Gabriel Ravier --- No idea why it was marked as x86-specific, it isn't as far as I can see, so I removed the target here. Do tell me if this is wrong. Referenced Bugs: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=19987 [Bug 19987] [meta-bug] fold missing optimizations in general
