using testcase ifcvt-4.c:
typedef int word __attribute__((mode(word)));
word
foo (word x, word y, word a)
{
word i = x;
word j = y;
/* Try to make taking the branch likely. */
__builtin_expect (x > y, 1);
if (x > y)
{
i = a;
j = i;
}
return i * j;
The current VRP2 pass takes:
if (x_3(D) > y_4(D))
goto <bb 3>; [50.00%] <<--- note the THEN target
else
goto <bb 4>; [50.00%]
;; succ: 3 [50.0% (guessed)] count:536870912 (estimated
locally) (TRUE_VALUE,EXECUTABLE)
;; 4 [50.0% (guessed)] count:536870912 (estimated
locally) (FALSE_VALUE,EXECUTABLE)
;; basic block 3, loop depth 0, count 536870912 (estimated locally),
maybe hot
;; prev block 2, next block 4, flags: (NEW, REACHABLE, VISITED)
;; pred: 2 [50.0% (guessed)] count:536870912 (estimated
locally) (TRUE_VALUE,EXECUTABLE)
;; succ: 4 [always] count:536870912 (estimated locally)
(FALLTHRU,EXECUTABLE)
;; basic block 4, loop depth 0, count 1073741824 (estimated locally),
maybe hot
;; prev block 3, next block 1, flags: (NEW, REACHABLE, VISITED)
;; pred: 2 [50.0% (guessed)] count:536870912 (estimated
locally) (FALSE_VALUE,EXECUTABLE)
;; 3 [always] count:536870912 (estimated locally)
(FALLTHRU,EXECUTABLE)
# i_1 = PHI <x_3(D)(2), a_5(D)(3)>
# j_2 = PHI <y_4(D)(2), a_5(D)(3)>
_6 = i_1 * j_2;
# VUSE <.MEM_7(D)>
return _6;
and turns it into :
;; basic block 2, loop depth 0, count 1073741824 (estimated locally),
maybe hot
;; prev block 0, next block 3, flags: (NEW, REACHABLE, VISITED)
;; pred: ENTRY [always] count:1073741824 (estimated locally)
(FALLTHRU,EXECUTABLE)
if (x_3(D) > y_4(D))
goto <bb 4>; [50.00%] <<-- has been reversed.
else
goto <bb 3>; [50.00%]
;; succ: 4 [50.0% (guessed)] count:536870912 (estimated
locally) (TRUE_VALUE,EXECUTABLE)
;; 3 [50.0% (guessed)] count:536870912 (estimated
locally) (FALSE_VALUE,EXECUTABLE)
;; basic block 3, loop depth 0, count 536870912 (estimated locally),
maybe hot
;; prev block 2, next block 4, flags: (NEW, VISITED)
;; pred: 2 [50.0% (guessed)] count:536870912 (estimated
locally) (FALSE_VALUE,EXECUTABLE)
;; succ: 4 [always] count:536870912 (estimated locally)
(FALLTHRU,EXECUTABLE)
;; basic block 4, loop depth 0, count 1073741824 (estimated locally),
maybe hot
;; prev block 3, next block 1, flags: (NEW, REACHABLE, VISITED)
;; pred: 3 [always] count:536870912 (estimated locally)
(FALLTHRU,EXECUTABLE)
;; 2 [50.0% (guessed)] count:536870912 (estimated
locally) (TRUE_VALUE,EXECUTABLE)
# i_1 = PHI <x_3(D)(3), a_5(D)(2)>
# j_2 = PHI <y_4(D)(3), a_5(D)(2)>
_6 = i_1 * j_2;
# VUSE <.MEM_7(D)>
return _6;
So the IF has reversed the targets (but not the condition), and the PHIs
in the target block have been adjusted.
Where does this happen? I cannot find it. There doesnt seem to be
anything in the IL which is reflecting the "expect" from the original
code.. and if I run ranger vrp instead of classic_vrp, we don't do
this... so I'm missing something....
Thanks
Andrew
