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Wed, 23 Nov 2016 03:49:19 -0800 (PST) In-Reply-To: References: From: Prathamesh Kulkarni Date: Wed, 23 Nov 2016 17:19:19 +0530 Message-ID: Subject: Re: PR78153 To: Richard Biener Cc: gcc Patches , Martin Sebor X-IsSubscribed: yes On 23 November 2016 at 15:16, Richard Biener wrote: > On Tue, 22 Nov 2016, Prathamesh Kulkarni wrote: > >> On 22 November 2016 at 20:53, Richard Biener wrote: >> > On Tue, 22 Nov 2016, Prathamesh Kulkarni wrote: >> > >> >> On 22 November 2016 at 20:18, Richard Biener wrote: >> >> > On Tue, 22 Nov 2016, Prathamesh Kulkarni wrote: >> >> > >> >> >> On 21 November 2016 at 15:10, Richard Biener 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; >> >> >> >> >> >> >> >> : >> >> >> >> 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; >> >> >> >> >> >> >> >> : >> >> >> >> 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; >> >> >> >> >> >> >> >> : >> >> >> >> 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; >> >> >> >> : >> >> 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). > Hi Richard, Does the attached patch look OK ? I verified it prevents the regression for above case. Bootstrap+test on x86_64-unknown-linux-gnu in progress. Thanks, Prathamesh > 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 >> >> > SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg) >> >> >> >> >> > >> > -- >> > Richard Biener >> > SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg) >> > > -- > Richard Biener > SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg) diff --git a/gcc/gimple-fold.c b/gcc/gimple-fold.c index aabc8ff..321dc85 100644 --- a/gcc/gimple-fold.c +++ b/gcc/gimple-fold.c @@ -4406,6 +4406,23 @@ fold_stmt_1 (gimple_stmt_iterator *gsi, bool inplace, tree (*valueize) (tree)) } break; + case GIMPLE_RETURN: + { + greturn *ret_stmt = as_a (stmt); + tree ret = gimple_return_retval(ret_stmt); + + if (ret && TREE_CODE (ret) == SSA_NAME && valueize) + { + tree val = valueize (ret); + if (val && TREE_CONSTANT (val)) + { + gimple_return_set_retval (ret_stmt, val); + changed = true; + } + } + } + break; + default:; } diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr78153-1.c b/gcc/testsuite/gcc.dg/tree-ssa/pr78153-1.c new file mode 100644 index 0000000..2530ba0 --- /dev/null +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr78153-1.c @@ -0,0 +1,10 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fdump-tree-evrp-slim" } */ + +void f(const char *s) +{ + if (__PTRDIFF_MAX__ <= __builtin_strlen (s)) + __builtin_abort (); +} + +/* { dg-final { scan-tree-dump-not "__builtin_abort" "evrp" } } */ diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr78153-2.c b/gcc/testsuite/gcc.dg/tree-ssa/pr78153-2.c new file mode 100644 index 0000000..de70450 --- /dev/null +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr78153-2.c @@ -0,0 +1,11 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fdump-tree-evrp-slim" } */ + +void f(const char *s) +{ + __PTRDIFF_TYPE__ n = __builtin_strlen (s); + if (n < 0) + __builtin_abort (); +} + +/* { dg-final { scan-tree-dump-not "__builtin_abort" "evrp" } } */ diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c index c2a4133..373582a 100644 --- a/gcc/tree-vrp.c +++ b/gcc/tree-vrp.c @@ -4013,6 +4013,16 @@ extract_range_basic (value_range *vr, gimple *stmt) : vrp_val_max (type), NULL); } return; + case CFN_BUILT_IN_STRLEN: + { + tree type = TREE_TYPE (gimple_call_lhs (stmt)); + tree max = vrp_val_max (ptrdiff_type_node); + wide_int wmax = wi::to_wide (max, TYPE_PRECISION (TREE_TYPE (max))); + tree range_min = build_zero_cst (type); + tree range_max = wide_int_to_tree (type, wmax - 1); + set_value_range (vr, VR_RANGE, range_min, range_max, NULL); + } + return; default: break; }