| Message ID | CAAgBjMms4U2LvcyKn6snYHKq92NqTs22PKgoOuabZ5DKNP-uDQ@mail.gmail.com |
|---|---|
| State | New |
| Headers | show |
On Tue, 22 Nov 2016, Prathamesh Kulkarni wrote: > On 22 November 2016 at 20:53, Richard Biener <rguenther@suse.de> wrote: > > On Tue, 22 Nov 2016, Prathamesh Kulkarni wrote: > > > >> On 22 November 2016 at 20:18, Richard Biener <rguenther@suse.de> wrote: > >> > On Tue, 22 Nov 2016, Prathamesh Kulkarni wrote: > >> > > >> >> On 21 November 2016 at 15:10, Richard Biener <rguenther@suse.de> wrote: > >> >> > On Sun, 20 Nov 2016, Prathamesh Kulkarni wrote: > >> >> > > >> >> >> Hi, > >> >> >> As suggested by Martin in PR78153 strlen's return value cannot exceed > >> >> >> PTRDIFF_MAX. > >> >> >> So I set it's range to [0, PTRDIFF_MAX - 1] in extract_range_basic() > >> >> >> in the attached patch. > >> >> >> > >> >> >> However it regressed strlenopt-3.c: > >> >> >> > >> >> >> Consider fn1() from strlenopt-3.c: > >> >> >> > >> >> >> __attribute__((noinline, noclone)) size_t > >> >> >> fn1 (char *p, char *q) > >> >> >> { > >> >> >> size_t s = strlen (q); > >> >> >> strcpy (p, q); > >> >> >> return s - strlen (p); > >> >> >> } > >> >> >> > >> >> >> The optimized dump shows the following: > >> >> >> > >> >> >> __attribute__((noclone, noinline)) > >> >> >> fn1 (char * p, char * q) > >> >> >> { > >> >> >> size_t s; > >> >> >> size_t _7; > >> >> >> long unsigned int _9; > >> >> >> > >> >> >> <bb 2>: > >> >> >> s_4 = strlen (q_3(D)); > >> >> >> _9 = s_4 + 1; > >> >> >> __builtin_memcpy (p_5(D), q_3(D), _9); > >> >> >> _7 = 0; > >> >> >> return _7; > >> >> >> > >> >> >> } > >> >> >> > >> >> >> which introduces the regression, because the test expects "return 0;" in fn1(). > >> >> >> > >> >> >> The issue seems to be in vrp2: > >> >> >> > >> >> >> Before the patch: > >> >> >> Visiting statement: > >> >> >> s_4 = strlen (q_3(D)); > >> >> >> Found new range for s_4: VARYING > >> >> >> > >> >> >> Visiting statement: > >> >> >> _1 = s_4; > >> >> >> Found new range for _1: [s_4, s_4] > >> >> >> marking stmt to be not simulated again > >> >> >> > >> >> >> Visiting statement: > >> >> >> _7 = s_4 - _1; > >> >> >> Applying pattern match.pd:111, gimple-match.c:27997 > >> >> >> Match-and-simplified s_4 - _1 to 0 > >> >> >> Intersecting > >> >> >> [0, 0] > >> >> >> and > >> >> >> [0, +INF] > >> >> >> to > >> >> >> [0, 0] > >> >> >> Found new range for _7: [0, 0] > >> >> >> > >> >> >> __attribute__((noclone, noinline)) > >> >> >> fn1 (char * p, char * q) > >> >> >> { > >> >> >> size_t s; > >> >> >> long unsigned int _1; > >> >> >> long unsigned int _9; > >> >> >> > >> >> >> <bb 2>: > >> >> >> s_4 = strlen (q_3(D)); > >> >> >> _9 = s_4 + 1; > >> >> >> __builtin_memcpy (p_5(D), q_3(D), _9); > >> >> >> _1 = s_4; > >> >> >> return 0; > >> >> >> > >> >> >> } > >> >> >> > >> >> >> > >> >> >> After the patch: > >> >> >> Visiting statement: > >> >> >> s_4 = strlen (q_3(D)); > >> >> >> Intersecting > >> >> >> [0, 9223372036854775806] > >> >> >> and > >> >> >> [0, 9223372036854775806] > >> >> >> to > >> >> >> [0, 9223372036854775806] > >> >> >> Found new range for s_4: [0, 9223372036854775806] > >> >> >> marking stmt to be not simulated again > >> >> >> > >> >> >> Visiting statement: > >> >> >> _1 = s_4; > >> >> >> Intersecting > >> >> >> [0, 9223372036854775806] EQUIVALENCES: { s_4 } (1 elements) > >> >> >> and > >> >> >> [0, 9223372036854775806] > >> >> >> to > >> >> >> [0, 9223372036854775806] EQUIVALENCES: { s_4 } (1 elements) > >> >> >> Found new range for _1: [0, 9223372036854775806] > >> >> >> marking stmt to be not simulated again > >> >> >> > >> >> >> Visiting statement: > >> >> >> _7 = s_4 - _1; > >> >> >> Intersecting > >> >> >> ~[9223372036854775807, 9223372036854775809] > >> >> >> and > >> >> >> ~[9223372036854775807, 9223372036854775809] > >> >> >> to > >> >> >> ~[9223372036854775807, 9223372036854775809] > >> >> >> Found new range for _7: ~[9223372036854775807, 9223372036854775809] > >> >> >> marking stmt to be not simulated again > >> >> >> > >> >> >> __attribute__((noclone, noinline)) > >> >> >> fn1 (char * p, char * q) > >> >> >> { > >> >> >> size_t s; > >> >> >> long unsigned int _1; > >> >> >> size_t _7; > >> >> >> long unsigned int _9; > >> >> >> > >> >> >> <bb 2>: > >> >> >> s_4 = strlen (q_3(D)); > >> >> >> _9 = s_4 + 1; > >> >> >> __builtin_memcpy (p_5(D), q_3(D), _9); > >> >> >> _1 = s_4; > >> >> >> _7 = s_4 - _1; > >> >> >> return _7; > >> >> >> > >> >> >> } > >> >> >> > >> >> >> Then forwprop4 turns > >> >> >> _1 = s_4 > >> >> >> _7 = s_4 - _1 > >> >> >> into > >> >> >> _7 = 0 > >> >> >> > >> >> >> and we end up with: > >> >> >> _7 = 0 > >> >> >> return _7 > >> >> >> in optimized dump. > >> >> >> > >> >> >> Running ccp again after forwprop4 trivially solves the issue, however > >> >> >> I am not sure if we want to run ccp again ? > >> >> >> > >> >> >> The issue is probably with extract_range_from_ssa_name(): > >> >> >> For _1 = s_4 > >> >> >> > >> >> >> Before patch: > >> >> >> VR for s_4 is set to varying. > >> >> >> So VR for _1 is set to [s_4, s_4] by extract_range_from_ssa_name. > >> >> >> Since VR for _1 is [s_4, s_4] it implicitly implies that _1 is equal to s_4, > >> >> >> and vrp is able to transform _7 = s_4 - _1 to _7 = 0 (by using > >> >> >> match.pd pattern x - x -> 0). > >> >> >> > >> >> >> After patch: > >> >> >> VR for s_4 is set to [0, PTRDIFF_MAX - 1] > >> >> >> And correspondingly VR for _1 is set to [0, PTRDIFF_MAX - 1] > >> >> >> so IIUC, we then lose the information that _1 is equal to s_4, > >> >> > > >> >> > We don't lose it, it's in its set of equivalencies. > >> >> Ah, I missed that, thanks. For some reason I had mis-conception that > >> >> equivalences stores > >> >> variables which have same value-ranges but are not necessarily equal. > >> >> > > >> >> >> and vrp doesn't transform _7 = s_4 - _1 to _7 = 0. > >> >> >> forwprop4 does that because it sees that s_4 and _1 are equivalent. > >> >> >> Does this sound correct ? > >> >> > > >> >> > Yes. So the issue is really that vrp_visit_assignment_or_call calls > >> >> > gimple_fold_stmt_to_constant_1 with vrp_valueize[_1] which when > >> >> > we do not have a singleton VR_RANGE does not fall back to looking > >> >> > at equivalences (there's not a good cheap way to do that currently because > >> >> > VRP doesn't keep a proper copy lattice but simply IORs equivalences > >> >> > from all equivalences). In theory simply using the first set bit > >> >> > might work. Thus sth like > >> >> > > >> >> > @@ -7057,6 +7030,12 @@ vrp_valueize (tree name) > >> >> > || is_gimple_min_invariant (vr->min)) > >> >> > && vrp_operand_equal_p (vr->min, vr->max)) > >> >> > return vr->min; > >> >> > + else if (vr->equiv && ! bitmap_empty_p (vr->equiv)) > >> >> > + { > >> >> > + unsigned num = bitmap_first_set_bit (vr->equiv); > >> >> > + if (num < SSA_NAME_VERSION (name)) > >> >> > + return ssa_name (num); > >> >> > + } > >> >> > } > >> >> > return name; > >> >> > } > >> >> > > >> >> > might work with the idea of simply doing canonicalization to one of > >> >> > the equivalences. But as we don't allow copies in the SSA def stmt > >> >> > (via vrp_valueize_1) I'm not sure that's good enough canonicalization. > >> >> IIUC, we record the equivalent variables in vr->equiv > >> >> but do not canonicalize to one of the equivalence like "copy-of value" > >> >> in copyprop ? > >> >> Using first set bit unfortunately doesn't help for the above case. > >> >> > >> >> Sorry if this sounds silly, should we just run copyprop/ccp once again > >> >> after vrp2 to ensure that there are no copies left ? > >> > > >> > why? forwprop also does copy and constant propagation. For the > >> > regression simply adjust the pass dump you scan. > >> Well, with the patch the redundant store to and load from _7 still remains > >> in optimized dump for fn1() in strlenopt-3.c: > >> > >> __attribute__((noclone, noinline)) > >> fn1 (char * p, char * q) > >> { > >> size_t s; > >> size_t _7; > >> long unsigned int _9; > >> > >> <bb 2>: > >> s_4 = strlen (q_3(D)); > >> _9 = s_4 + 1; > >> __builtin_memcpy (p_5(D), q_3(D), _9); > >> _7 = 0; > >> return _7; > >> > >> } > >> > >> Running ccp again after forwprop4 would get rid of _7. > >> Without the patch we have return _0; in optimized dump. > > > > Ah, but then that's a missing "folding" of the return. It's not > > a load/store anyway. > Hi Richard, > Thanks for the suggestion. In the attached untested patch, I tried to > modify forwprop to fold return-value to constant. > The optimized dump shows return 0; for the above test-case with this patch. > Does it look OK ? No, the fix is to make fold_stmt_1 handle GIMPLE_RETURN and simply valueize the return value (note 'valueize' might return NULL or be NULL). Richard. > > Thanks, > Prathamesh > > > > Richard. > > > >> Thanks, > >> Prathamesh > >> > > >> >> However that might be quite expensive ? > >> >> Or make vrp track copies like copyprop using a separate copy-of lattice ? > >> > > >> > Ideally we'd unify the three SSA propagation passes into one. We'd > >> > have to have separate lattices for copy&constant and range&known-bits. > >> > > >> > Richard. > >> > > >> >> Thanks, > >> >> Prathamesh > >> >> > > >> >> > Richard. > >> >> > >> >> > >> > > >> > -- > >> > Richard Biener <rguenther@suse.de> > >> > SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg) > >> > >> > > > > -- > > Richard Biener <rguenther@suse.de> > > SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg) > -- Richard Biener <rguenther@suse.de> SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)
diff --git a/gcc/tree-ssa-forwprop.c b/gcc/tree-ssa-forwprop.c index ed11b32..b4dce91 100644 --- a/gcc/tree-ssa-forwprop.c +++ b/gcc/tree-ssa-forwprop.c @@ -2155,6 +2155,8 @@ pass_forwprop::execute (function *fun) postorder, false); auto_vec<gimple *, 4> to_fixup; to_purge = BITMAP_ALLOC (NULL); + auto_vec<greturn *> ret_stmts; + for (int i = 0; i < postorder_num; ++i) { gimple_stmt_iterator gsi; @@ -2197,6 +2199,9 @@ pass_forwprop::execute (function *fun) tree lhs, rhs; enum tree_code code; + if (greturn *ret_stmt = dyn_cast<greturn *> (stmt)) + ret_stmts.safe_push (ret_stmt); + if (!is_gimple_assign (stmt)) { gsi_next (&gsi); @@ -2533,6 +2538,26 @@ pass_forwprop::execute (function *fun) cfg_changed |= fixup_noreturn_call (stmt); } + for (unsigned i = 0; i < ret_stmts.length (); ++i) + { + greturn *ret_stmt = ret_stmts[i]; + tree ret = gimple_return_retval (ret_stmt); + if (ret && TREE_CODE (ret) == SSA_NAME) + { + gimple *def_stmt = SSA_NAME_DEF_STMT (ret); + if (gassign *ga = dyn_cast<gassign *> (def_stmt)) + { + enum tree_code code = gimple_assign_rhs_code (def_stmt); + if (TREE_CODE_CLASS (code) == tcc_constant) + { + tree cst = gimple_assign_rhs1 (ga); + gimple_return_set_retval (ret_stmt, cst); + update_stmt (ret_stmt); + } + } + } + } + cfg_changed |= gimple_purge_all_dead_eh_edges (to_purge); BITMAP_FREE (to_purge);