https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81184
Martin Liška <marxin at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2017-06-23
CC| |jakub at gcc dot gnu.org
Assignee|unassigned at gcc dot gnu.org |marxin at gcc dot
gnu.org
Ever confirmed|0 |1
--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Confirmed, I'm adding Jakub as author of original test-case.
The affected function changed from:
Optimizing range tests c_2(D) -[0, 31] and -[32, 32]
into c_2(D) > 32
Removing basic block 3
;; basic block 3, loop depth 0
;; pred:
;; succ: 4
fix_loop_structure: fixing up loops for function
f6 (unsigned char c)
{
int _1;
_Bool _5;
<bb 2> [100.00%] [count: INV]:
if (c_2(D) == 34)
goto <bb 5>; [18.79%] [count: INV]
else
goto <bb 3>; [81.21%] [count: INV]
<bb 3> [65.95%] [count: INV]:
_5 = c_2(D) <= 32;
if (_5 != 0)
goto <bb 5>; [31.00%] [count: INV]
else
goto <bb 4>; [69.00%] [count: INV]
<bb 4> [45.51%] [count: INV]:
<bb 5> [100.00%] [count: INV]:
# _1 = PHI <2(2), 0(4), 2(3)>
return _1;
}
to:
Optimizing range tests c_2(D) -[32, 32] and -[34, 34]
into (c_2(D) & 253) != 32
Width = 1 was chosen for reassociation
Merging blocks 2 and 3
fix_loop_structure: fixing up loops for function
f6 (unsigned char c)
{
int _1;
_Bool _4;
unsigned char _5;
<bb 2> [100.00%] [count: INV]:
_5 = c_2(D) & 253;
_4 = _5 == 32;
if (_4 != 0)
goto <bb 5>; [10.65%] [count: INV]
else
goto <bb 3>; [89.35%] [count: INV]
<bb 3> [79.83%] [count: INV]:
if (c_2(D) <= 31)
goto <bb 4>; [18.79%] [count: INV]
else
goto <bb 5>; [81.21%] [count: INV]
<bb 4> [15.00%] [count: INV]:
<bb 5> [100.00%] [count: INV]:
# _1 = PHI <0(3), 2(2), 2(4)>
return _1;
}
On x86_64 it's different because the function looks as follows:
f6 (unsigned char c)
{
int _1;
_Bool _4;
_Bool _5;
_Bool _7;
_Bool _8;
_Bool _9;
<bb 2> [100.00%] [count: INV]:
_5 = c_2(D) == 32;
_4 = c_2(D) == 34;
_9 = c_2(D) <= 32;
_7 = c_2(D) <= 31;
_8 = _9 | _4;
if (_8 != 0)
goto <bb 3>; [15.00%] [count: INV]
else
goto <bb 4>; [85.00%] [count: INV]
<bb 3> [15.00%] [count: INV]:
<bb 4> [100.00%] [count: INV]:
# _1 = PHI <0(2), 2(3)>
return _1;
}
Note that the PR exposes problem where we are able to do predictions for
conditions, but
here we transform:
if (c_2(D) == 34)
goto <bb 3>; [10.65%] [count: INV]
else
goto <bb 4>; [89.35%] [count: INV]
into:
_4 = c_2(D) == 34;
and then we do
_8 = _9 | _4;
if (_8 != 0)
It's related to PR79489.
