https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102800
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Last reconfirmed| |2021-10-17
Status|UNCONFIRMED |NEW
Keywords| |missed-optimization
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
end_10 = begin_9(D) + _3;
if (begin_9(D) != end_10)
goto <bb 3>; [INV]
else
goto <bb 5>; [INV]
;; succ: 3 (TRUE_VALUE,EXECUTABLE)
;; 5 (FALSE_VALUE,EXECUTABLE)
;; basic block 3, loop depth 0, maybe hot
;; prev block 2, next block 4, flags: (NEW, VISITED)
;; pred: 2 (TRUE_VALUE,EXECUTABLE)
# RANGE [0, 7] NONZERO 7
_15 = (signed long) _3;
;; basic block 4, loop depth 1, maybe hot
;; prev block 3, next block 5, flags: (NEW, VISITED)
;; pred: 3 (FALLTHRU,EXECUTABLE)
;; 4 (TRUE_VALUE,EXECUTABLE)
# RANGE [-9223372036854775808, 7]
# x_6 = PHI <_15(3), x_14(4)>
# .MEM_7 = PHI <.MEM_11(D)(3), .MEM_13(4)>
_4 = (charD.7) x_6;
# RANGE [-128, 127]
_5 = (intD.6) _4;
# .MEM_13 = VDEF <.MEM_7>
# USE = nonlocal escaped
# CLB = nonlocal escaped
barD.1978 (_5);
# RANGE [-9223372036854775808, 6]
x_14 = x_6 + -1;
if (x_14 != 0)
goto <bb 4>; [INV]
else
goto <bb 5>; [INV]
;; succ: 4 (TRUE_VALUE,EXECUTABLE)
;; 5 (FALSE_VALUE,EXECUTABLE)
this is from evrp. Oh We miss that _15 cannot be 1.
even though later on we can detect it.
SO simple testcase:
void bar(char x);
void link_error(void);
void foo(char * begin)
{
// end = ALIGN(begin, 8);
__SIZE_TYPE__ t = 7 - ((((unsigned long)begin) - 1) % 8);
char * end = begin + t;
if (begin != end) {
if (!t) link_error();
long long x = end - begin;
do bar(x);
while(--x != 0);
}
}
The call to should really be removed in evrp.
So forwprop1 does not change the first begin!=end to t!=0 but changes
end-begin. to (long long)t. And then forwprop2 changes begin!=end to t!=0 and
vrp1 can then figure out the range of x inside the loop is [1,7].
