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From: "amacleod at redhat dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/97434] Missed dead code optimization from data flow analysis Date: Sat, 21 Nov 2020 00:48:23 +0000 [thread overview] Message-ID: <bug-97434-4-Tc8AO4hEpV@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-97434-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97434 Andrew Macleod <amacleod at redhat dot com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |amacleod at redhat dot com --- Comment #2 from Andrew Macleod <amacleod at redhat dot com> --- =========== BB 2 ============ <bb 2> : _1 = random_number (); a_11 = (unsigned int) _1; _2 = random_number (); b_13 = (unsigned int) _2; if (a_11 < b_13) goto <bb 3>; [INV] else goto <bb 4>; [INV] 2->3 (T) _2 : int [-INF, -1][1, +INF] 2->3 (T) b_13 : unsigned int [1, +INF] =========== BB 3 ============ <bb 3> : // predicted unlikely by early return (on trees) predictor. goto <bb 6>; [INV] =========== BB 4 ============ a_11 unsigned int VARYING b_13 unsigned int VARYING <bb 4> : _3 = b_13 + 4294967288; x_14 = (int) _3; _4 = x_14 > 0; _6 = _3 > a_11; _7 = _4 & _6; if (_7 != 0) goto <bb 5>; [INV] else goto <bb 6>; [INV] 4->5 (T) _3 : unsigned int [1, 2147483647] 4->5 (T) _4 : _Bool [1, 1] 4->5 (T) _6 : _Bool [1, 1] 4->5 (T) _7 : _Bool [1, 1] 4->5 (T) a_11 : unsigned int [0, 4294967294] 4->5 (T) b_13 : unsigned int [9, 2147483655] 4->5 (T) x_14 : int [1, +INF] 4->6 (F) _7 : _Bool [0, 0] When relations are implemented, the edge from 2->4 should record a_11 >= b_13 as long as we get it right that x_14 is a cast equivalence of _3, and its > 0, then we should be able to also determine that _3 is < b_13 and therefore < a_11 always, and fold this away. A good testcase to confirm all the parts are working together.. when we get there.. hopefully next release.
next prev parent reply other threads:[~2020-11-21 0:48 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-10-15 1:38 [Bug c/97434] New: " jwerner at chromium dot org 2020-10-15 7:32 ` [Bug tree-optimization/97434] " rguenth at gcc dot gnu.org 2020-11-21 0:48 ` amacleod at redhat dot com [this message] 2021-12-16 0:12 ` pinskia at gcc dot gnu.org
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