http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58377
--- Comment #9 from davidxl at google dot com --- (In reply to Richard Biener from comment #5) > Confirmed with the C++ FE, works with the C FE. Does not warn on trunk (for > no good reason I think, the reason seems to be presence of loop structure > and thus some extra BBs). > > Difference: > > trunk: > > [WORKLIST]: add to initial list: out_2 = PHI <out_8(D)(2), out_1(8)> > [CHECK]: examining phi: out_2 = PHI <out_8(D)(2), out_1(8)> > > Use in stmt out_1 = PHI <out_12(4), out_12(5), out_2(3)> > is guarded by : > if (pop_first_bucket.2_10 != 0) > > [CHECK] Found def edge 0 in out_1 = PHI <out_12(4), out_12(5), out_2(3)> > > [CHECK] Found def edge 1 in out_1 = PHI <out_12(4), out_12(5), out_2(3)> > Operand defs of phi out_2 = PHI <out_8(D)(2), out_1(8)> > is guarded by : > if (out_12 != 0) > [CHECK]: Found unguarded use: out_1 = PHI <out_12(4), out_12(5), out_2(3)> > [WORKLIST]: Update worklist with phi: out_1 = PHI <out_12(4), out_12(5), > out_2(3)> > [CHECK]: examining phi: out_1 = PHI <out_12(4), out_12(5), out_2(3)> > > Use in stmt out_2 = PHI <out_8(D)(2), out_1(8)> > is guarded by : > (.NOT.) if (iftmp.1_3 != 0) > > [CHECK] Found def edge 0 in out_1 = PHI <out_12(4), out_12(5), out_2(3)> > > [CHECK] Found def edge 1 in out_1 = PHI <out_12(4), out_12(5), out_2(3)> > Operand defs of phi out_1 = PHI <out_12(4), out_12(5), out_2(3)> > is guarded by : > if (pop_first_bucket.2_10 != 0) > (.AND.) > if (out_12 != 0) > (.OR.) > if (pop_first_bucket.2_10 != 0) > (.AND.) > (.NOT.) if (out_12 != 0) > > Normalized to > Operand defs of phi out_1 = PHI <out_12(4), out_12(5), out_2(3)> > is guarded by : > if (pop_first_bucket.2_10 != 0) > ... > > vs. 4.8 branch: > > [WORKLIST]: add to initial list: out_2 = PHI <out_8(D)(2), out_1(6)> > [CHECK]: examining phi: out_2 = PHI <out_8(D)(2), out_1(6)> > > Use in stmt out_1 = PHI <out_12(4), out_12(5), out_2(3)> > is guarded by : > if (pop_first_bucket.2_10 != 0) > > [CHECK] Found def edge 0 in out_1 = PHI <out_12(4), out_12(5), out_2(3)> > > [CHECK] Found def edge 1 in out_1 = PHI <out_12(4), out_12(5), out_2(3)> > Operand defs of phi out_2 = PHI <out_8(D)(2), out_1(6)> > is guarded by : > if (out_12 != 0) > [CHECK]: Found unguarded use: out_1 = PHI <out_12(4), out_12(5), out_2(3)> > [WORKLIST]: Update worklist with phi: out_1 = PHI <out_12(4), out_12(5), > out_2(3)> > [CHECK]: examining phi: out_1 = PHI <out_12(4), out_12(5), out_2(3)> > [CHECK]: Found unguarded use: out_2 = PHI <out_8(D)(2), out_1(6)> > [CHECK]: Found unguarded use: _4 = PHI <out_1(6), 0(7)> > [WORKLIST]: Update worklist with phi: _4 = PHI <out_1(6), 0(7)> > [CHECK]: examining phi: _4 = PHI <out_1(6), 0(7)> > [CHECK]: Found unguarded use: return _4; > > The IL difference is that we have > > <bb 6>: > # out_1 = PHI <out_12(4), out_12(5), out_2(3)> > # iftmp.1_3 = PHI <1(4), 0(5), 0(3)> > if (iftmp.1_3 != 0) > goto <bb 7>; > else > goto <bb 8>; > > <bb 7>: > out_13 = out_1; > goto <bb 10>; > ... > <bb 10>: > # _4 = PHI <out_13(7), 0(9)> > return _4; > > which doesn't warn vs. > > <bb 6>: > # out_1 = PHI <out_12(4), out_12(5), out_2(3)> > # iftmp.1_3 = PHI <1(4), 0(5), 0(3)> > if (iftmp.1_3 != 0) > goto <bb 8>; > else > goto <bb 7>; > ... > <bb 8>: > # _4 = PHI <out_1(6), 0(7)> > return _4; > > which does. The issue seems to be that the analysis doesn't consider > the PHI uses in > > if (iftmp.1_3 != 0) > goto <bb 8>; > else > goto <bb 7>; > > <bb 7>: > # out_2 = PHI <out_8(D)(2), out_1(6)> > > guarded by anything (the out_1 use is guarded by iftmp.1_3 == 0). > > David - the code does > > if (gimple_code (use_stmt) == GIMPLE_PHI) > use_bb = gimple_phi_arg_edge (use_stmt, > PHI_ARG_INDEX_FROM_USE (use_p))->src; > else > use_bb = gimple_bb (use_stmt); > > if (is_use_properly_guarded (use_stmt, > use_bb, > ... > > so it chooses the source block (as approximation?). > > Splitting all edges results in us no longer warning here and: > > Use in stmt out_2 = PHI <out_8(D)(15), out_1(16)> > is guarded by : > (.NOT.) if (iftmp.1_3 != 0) > > Can you see to fix that please? Thanks. Your analysis is correct -- the use is indeed guarded. I forgot why I chose to use the phi arg's source BB. Will take a look. David
