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From: "dberlin at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/23588] New: CCP not fully propagating constants Date: Sat, 27 Aug 2005 03:31:00 -0000 [thread overview] Message-ID: <20050827022854.23588.dberlin@gcc.gnu.org> (raw) Consider int main(int a, int b, int c, int d) { d = -1; int e = (a | b) | (c | d); int f = (c | a) | (b | d); return e | f; } Because d == -1, the whole thing folds to return -1; CCP doesn't do this however. It takes: # BLOCK 0 # PRED: ENTRY (fallthru) d_1 = -1; D.1285_4 = a_2 | b_3; D.1286_6 = c_5 | d_1; e_7 = D.1285_4 | D.1286_6; D.1287_8 = c_5 | a_2; D.1288_9 = b_3 | d_1; f_10 = D.1287_8 | D.1288_9; D.1289_12 = e_7 | f_10; return D.1289_12; # SUCC: EXIT and turns it into main (a, b, c, d) { int f; int e; int D.1289; int D.1288; int D.1287; int D.1286; int D.1285; # BLOCK 0 # PRED: ENTRY (fallthru,exec) d_1 = -1; D.1285_4 = a_2 | b_3; D.1286_6 = -1; e_7 = D.1285_4 | D.1286_6; D.1287_8 = c_5 | a_2; D.1288_9 = -1; f_10 = D.1287_8 | D.1288_9; D.1289_12 = e_7 | f_10; return D.1289_12; # SUCC: EXIT } (note that it's not actually following the use edges, or it would have folded it all the way) The propagation looks broken: ;; Function main (main) Immediate_uses: d_1 : -->2 uses. D.1288_9 = b_3 | d_1; D.1286_6 = c_5 | d_1; a_2 : -->2 uses. D.1287_8 = c_5 | a_2; D.1285_4 = a_2 | b_3; b_3 : -->2 uses. D.1288_9 = b_3 | d_1; D.1285_4 = a_2 | b_3; D.1285_4 : --> single use. e_7 = D.1285_4 | D.1286_6; c_5 : -->2 uses. D.1287_8 = c_5 | a_2; D.1286_6 = c_5 | d_1; D.1286_6 : --> single use. e_7 = D.1285_4 | D.1286_6; e_7 : --> single use. D.1289_12 = e_7 | f_10; D.1287_8 : --> single use. f_10 = D.1287_8 | D.1288_9; D.1288_9 : --> single use. f_10 = D.1287_8 | D.1288_9; f_10 : --> single use. D.1289_12 = e_7 | f_10; D.1289_12 : --> single use. return D.1289_12; <retval>_13 : --> no uses. Simulating block 0 Visiting statement: d_1 = -1; Lattice value changed to CONSTANT -1. Adding SSA edges to worklist. Substituing values and folding statements Folded statement: D.1286_6 = c_5 | d_1; into: D.1286_6 = -1; Folded statement: D.1288_9 = b_3 | d_1; into: D.1288_9 = -1; Constants propagated: 2 Copies propagated: 0 Predicates folded: 0 If it had actually added the ssa edges to the worklist, followed them, and folded the statements containing the new constant, it would have gotten the right answer. -- Summary: CCP not fully propagating constants Product: gcc Version: 4.1.0 Status: UNCONFIRMED Severity: enhancement Priority: P2 Component: tree-optimization AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: dberlin at gcc dot gnu dot org CC: dnovillo at gcc dot gnu dot org,gcc-bugs at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23588
next reply other threads:[~2005-08-27 2:29 UTC|newest] Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2005-08-27 3:31 dberlin at gcc dot gnu dot org [this message] 2005-08-27 3:31 ` [Bug tree-optimization/23588] " pinskia at gcc dot gnu dot org 2005-09-07 3:46 ` pinskia at gcc dot gnu dot org 2005-09-07 3:51 ` pinskia at gcc dot gnu dot org 2005-09-07 4:28 ` pinskia at gcc dot gnu dot org 2005-09-07 13:36 ` dberlin at dberlin dot org 2005-09-21 15:02 ` steven at gcc dot gnu dot org
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