https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52078
Jeffrey A. Law <law at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
CC| |law at redhat dot com
Resolution|--- |FIXED
--- Comment #3 from Jeffrey A. Law <law at redhat dot com> ---
If we look at the VRP dump after ASSERT_EXPR insertion it's obvious what needs
to happen here:
; basic block 2, loop depth 0, count 0, freq 10000, maybe hot
;; prev block 0, next block 7, flags: (NEW, REACHABLE, VISITED)
;; pred: ENTRY [100.0%] (FALLTHRU,EXECUTABLE)
if (nname_6(D) != oname_7(D))
goto <bb 3>; [70.00%]
else
goto <bb 7>; [30.00%]
;; succ: 3 [70.0%] (TRUE_VALUE,EXECUTABLE)
;; 7 [30.0%] (FALSE_VALUE,EXECUTABLE)
;; basic block 7, loop depth 0, count 0, freq 3000, maybe hot
;; prev block 2, next block 3, flags: (NEW)
;; pred: 2 [30.0%] (FALSE_VALUE,EXECUTABLE)
nname_12 = ASSERT_EXPR <nname_6(D), nname_6(D) == oname_7(D)>;
oname_15 = ASSERT_EXPR <oname_7(D), oname_7(D) == nname_12>;
goto <bb 4>; [100.00%]
;; succ: 4 [100.0%] (FALLTHRU)
;; basic block 3, loop depth 0, count 0, freq 7000, maybe hot
;; prev block 7, next block 4, flags: (NEW, REACHABLE, VISITED)
;; pred: 2 [70.0%] (TRUE_VALUE,EXECUTABLE)
nname_11 = ASSERT_EXPR <nname_6(D), nname_6(D) != oname_7(D)>;
oname_14 = ASSERT_EXPR <oname_7(D), oname_7(D) != nname_11>;
_10 = __builtin_strcmp (nname_11, oname_14);
oname_16 = ASSERT_EXPR <oname_14, oname_14 != 0B>;
nname_13 = ASSERT_EXPR <nname_11, nname_11 != 0B>;
;; succ: 4 [100.0%] (FALLTHRU,EXECUTABLE)
;; basic block 4, loop depth 0, count 0, freq 10000, maybe hot
;; prev block 3, next block 5, flags: (NEW, REACHABLE, VISITED)
;; pred: 3 [100.0%] (FALLTHRU,EXECUTABLE)
;; 7 [100.0%] (FALLTHRU)
# cmp_4 = PHI <_10(3), cmp_8(D)(7)>
_1 = nname_6(D) == oname_7(D);
_2 = cmp_4 == 0;
_3 = _1 | _2;
if (_3 != 0)
goto <bb 6>; [46.00%]
else
goto <bb 5>; [54.00%]
;; succ: 6 [46.0%] (TRUE_VALUE,EXECUTABLE)
;; 5 [54.0%] (FALSE_VALUE,EXECUTABLE)
If we traverse the edge 2->7, then we know that nname == oname (which is shown
in the IL via the ASSERT_EXPRs in BB7). We can use that to simplify the
computation of _3 in BB4 and ultimately thread 2->7->6 and eliminate the test
of cmp_4 on the threaded path (it becomes dead).
That eliminates the uninitialized use.
This is fixed on the trunk, most likely due to the work for pr71437 which looks
to exploit ASSERT_EXPRs more aggressively.
