https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98365
Bug ID: 98365
Summary: Miss vectoization
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: crazylht at gmail dot com
CC: hjl.tools at gmail dot com, wwwhhhyyy333 at gmail dot com
Target Milestone: ---
Host: x86_64-pc-linux-gnu
cat test.c
int foo (char a[64], char c[64])
{
int i;
char cnt=0;
for (int i = 0;i != 64; i++)
if (a[i] == c[i])
cnt++;
return cnt;
}
with -Ofast -mavx2 gcc failed to vectorize the loop due to
dump of loop body:
-----------
# cnt_21 = PHI <cnt_9(7), 0(15)>
# i_22 = PHI <i_17(7), 0(15)>
# ivtmp_19 = PHI <ivtmp_18(7), 64(15)>
_1 = (sizetype) i_22;
_2 = a_14(D) + _1;
_3 = *_2;
_5 = c_15(D) + _1;
_6 = *_5;
cnt.1_7 = (unsigned char) cnt_21;
_8 = cnt.1_7 + 1;
cnt_16 = (char) _8;
cnt_9 = _3 == _6 ? cnt_16 : cnt_21;
i_17 = i_22 + 1;
ivtmp_18 = ivtmp_19 - 1;
----------
-fopt-info
---------
test.c:5:20: note: vec_stmt_relevant_p: stmt live but not relevant.
test.c:5:20: note: mark relevant 1, live 1: cnt_9 = _3 == _6 ? cnt_16 :
cnt_21;
test.c:5:20: note: init: stmt relevant? i_17 = i_22 + 1;
test.c:5:20: note: init: stmt relevant? ivtmp_18 = ivtmp_19 - 1;
test.c:5:20: note: init: stmt relevant? if (ivtmp_18 != 0)
test.c:5:20: note: worklist: examine stmt: cnt_9 = _3 == _6 ? cnt_16 :
cnt_21;
test.c:5:20: note: vect_is_simple_use: operand *_2, type of def: internal
test.c:5:20: note: mark relevant 1, live 0: _3 = *_2;
test.c:5:20: note: vect_is_simple_use: operand *_5, type of def: internal
test.c:5:20: note: mark relevant 1, live 0: _6 = *_5;
test.c:5:20: note: vect_is_simple_use: operand (char) _8, type of def:
internal
test.c:5:20: note: mark relevant 1, live 0: cnt_16 = (char) _8;
test.c:5:20: note: vect_is_simple_use: operand cnt_21 = PHI <cnt_9(7),
0(15)>, type of def: unknown
test.c:5:20: missed: Unsupported pattern.
----------------
Shouldn't cnt_21 = PHI <cnt_9(7), 0(15)>, stmt relevant?
BTW: with extra -fwrapv, gcc successfully vectorized the loop.
