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From: "patrick at parcs dot ath.cx" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/61112] Simple example triggers false-positive -Wmaybe-uninitialized warning Date: Thu, 08 May 2014 16:27:00 -0000 [thread overview] Message-ID: <bug-61112-4-sRwoIDiAuZ@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-61112-4@http.gcc.gnu.org/bugzilla/> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=61112 --- Comment #2 from patrick at parcs dot ath.cx --- Relevant contents of -fdump-tree-uninit: [WORKLIST]: Update worklist with phi: w_2 = PHI <w_1(5), 10(10)> [CHECK]: examining phi: w_2 = PHI <w_1(5), 10(10)> [CHECK] Found def edge 1 in w_1 = PHI <w_5(D)(3), z_6(D)(9)> [CHECK] Found def edge 1 in w_2 = PHI <w_1(5), 10(10)> [AFTER NORMALIZATION -- [USE]: p = w_2; is guarded by : y_7(D) != 0 (.OR.) x_4(D) != 0 [AFTER NORMALIZATION -- [DEF]: w_2 = PHI <w_1(5), 10(10)> is guarded by : y_7(D) != 0 [CHECK]: Found unguarded use: p = w_2; void void foo(int, int, int) (int x, int y, int z) { int w; int _8; <bb 2>: if (x_4(D) != 0) goto <bb 9>; else goto <bb 3>; <bb 9>: goto <bb 4>; <bb 3>: <bb 4>: # w_1 = PHI <w_5(D)(3), z_6(D)(9)> if (y_7(D) != 0) goto <bb 10>; else goto <bb 5>; <bb 10>: goto <bb 6>; <bb 5>: <bb 6>: # w_2 = PHI <w_1(5), 10(10)> _8 = x_4(D) | y_7(D); if (_8 != 0) goto <bb 7>; else goto <bb 11>; <bb 11>: goto <bb 8>; <bb 7>: p = w_2; <bb 8>: return; } uninit analysis correctly detects two defining edges but one of the edges (src=bb 9, dest=bb 4) flows into the control dependence root (bb 6). Since this edge can not be reached downwards from the CD root, it is not considered when reconstructing the predicate chain that guards the definition of w_2. As a result, an incomplete def predicate chain is computed and a warning is emitted. If instead the control dependence root was bb 2 then the aforementioned edge would not get discarded (because the edge could be reached from bb 2) and so the computed def predicate chain would be complete. I have a patch that fixes this issue.
next prev parent reply other threads:[~2014-05-08 16:27 UTC|newest] Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2014-05-08 14:07 [Bug middle-end/61112] New: " patrick at parcs dot ath.cx 2014-05-08 14:08 ` [Bug middle-end/61112] " patrick at parcs dot ath.cx 2014-05-08 16:27 ` patrick at parcs dot ath.cx [this message] 2021-03-29 19:54 ` cvs-commit at gcc dot gnu.org 2021-03-29 20:03 ` msebor at gcc dot gnu.org 2021-03-30 16:42 ` manu at gcc dot gnu.org 2021-11-30 14:44 ` aldyh at gcc dot gnu.org
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