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On 6 May 2016 at 17:20, Richard Biener <rguenther@suse.de> wrote: > On Wed, 4 May 2016, Prathamesh Kulkarni wrote: > >> On 23 February 2016 at 21:49, Prathamesh Kulkarni >> <prathamesh.kulkarni@linaro.org> wrote: >> > On 23 February 2016 at 17:31, Richard Biener <rguenther@suse.de> wrote: >> >> On Tue, 23 Feb 2016, Prathamesh Kulkarni wrote: >> >> >> >>> On 22 February 2016 at 17:36, Richard Biener <rguenther@suse.de> wrote: >> >>> > On Mon, 22 Feb 2016, Prathamesh Kulkarni wrote: >> >>> > >> >>> >> Hi Richard, >> >>> >> As discussed in private mail, this version of patch attempts to >> >>> >> increase alignment >> >>> >> of global struct decl if it contains an an array field(s) and array's >> >>> >> offset is a multiple of the alignment of vector type corresponding to >> >>> >> it's scalar type and recursively checks for nested structs. >> >>> >> eg: >> >>> >> static struct >> >>> >> { >> >>> >> int a, b, c, d; >> >>> >> int k[4]; >> >>> >> float f[10]; >> >>> >> }; >> >>> >> k is a candidate array since it's offset is 16 and alignment of >> >>> >> "vector (4) int" is 8. >> >>> >> Similarly for f. >> >>> >> >> >>> >> I haven't been able to create a test-case where there are >> >>> >> multiple candidate arrays and vector alignment of arrays are different. >> >>> >> I suppose in this case we will have to increase alignment >> >>> >> of the struct by the max alignment ? >> >>> >> eg: >> >>> >> static struct >> >>> >> { >> >>> >> <fields> >> >>> >> T1 k[S1] >> >>> >> <fields> >> >>> >> T2 f[S2] >> >>> >> <fields> >> >>> >> }; >> >>> >> >> >>> >> if V1 is vector type corresponding to T1, and V2 corresponding vector >> >>> >> type to T2, >> >>> >> offset (k) % align(V1) == 0 and offset (f) % align(V2) == 0 >> >>> >> and align (V1) > align(V2) then we will increase alignment of struct >> >>> >> by align(V1). >> >>> >> >> >>> >> Testing showed FAIL for g++.dg/torture/pr31863.C due to program timeout. >> >>> >> Initially it appeared to me, it went in infinite loop. However >> >>> >> on second thoughts I think it's probably not an infinite loop, rather >> >>> >> taking (extraordinarily) large amount of time >> >>> >> to compile the test-case with the patch. >> >>> >> The test-case builds quickly for only 2 instantiations of ClassSpec >> >>> >> (ClassSpec<Key, A001, 1>, >> >>> >> ClassSpec<Key, A002, 2>) >> >>> >> Building with 22 instantiations (upto ClassSpec<Key, A0023, 22>) takes up >> >>> >> to ~1m to compile. >> >>> >> with: >> >>> >> 23 instantiations: ~2m >> >>> >> 24 instantiations: ~5m >> >>> >> For 30 instantiations I terminated cc1plus after 13m (by SIGKILL). >> >>> >> >> >>> >> I guess it shouldn't go in an infinite loop because: >> >>> >> a) structs cannot have circular references. >> >>> >> b) works for lower number of instantiations >> >>> >> However I have no sound evidence that it cannot be in infinite loop. >> >>> >> I don't understand why a decl node is getting visited more than once >> >>> >> for that test-case. >> >>> >> >> >>> >> Using a hash_map to store alignments of decl's so that decl node gets visited >> >>> >> only once prevents the issue. >> >>> > >> >>> > Maybe aliases. Try not walking vnode->alias == true vars. >> >>> Hi, >> >>> I have a hypothesis why decl node gets visited multiple times. >> >>> >> >>> Consider the test-case: >> >>> template <typename T, unsigned N> >> >>> struct X >> >>> { >> >>> T a; >> >>> virtual int foo() { return N; } >> >>> }; >> >>> >> >>> typedef struct X<int, 1> x_1; >> >>> typedef struct X<int ,2> x_2; >> >>> >> >>> static x_1 obj1 __attribute__((used)); >> >>> static x_2 obj2 __attribute__((used)); >> >>> >> >>> Two additional structs are created by C++FE, c++filt shows: >> >>> _ZTI1XIiLj1EE -> typeinfo for X<int, 1u> >> >>> _ZTI1XIiLj2EE -> typeinfo for X<int, 2u> >> >>> >> >>> Both of these structs have only one field D.2991 and it appears it's >> >>> *shared* between them: >> >>> struct D.2991; >> >>> const void * D.2980; >> >>> const char * D.2981; >> >>> >> >>> Hence the decl node D.2991 and it's fields (D.2890, D.2981) get visited twice: >> >>> once when walking _ZTI1XIiLj1EE and 2nd time when walking _ZTI1XIiLj2EE >> >>> >> >>> Dump of walking over the global structs for above test-case: >> >>> http://pastebin.com/R5SABW0c >> >>> >> >>> So it appears to me to me a DAG (interior node == struct decl, leaf == >> >>> non-struct field, >> >>> edge from node1 -> node2 if node2 is field of node1) is getting >> >>> created when struct decl >> >>> is a type-info object. >> >>> >> >>> I am not really clear on how we should proceed: >> >>> a) Keep using hash_map to store alignments so that every decl gets >> >>> visited only once. >> >>> b) Skip walking artificial record decls. >> >>> I am not sure if skipping all artificial struct decls would be a good >> >>> idea, but I don't >> >>> think it's possible to identify if a struct-decl is typeinfo struct at >> >>> middle-end ? >> >> >> >> You shouldn't end up walking those when walking the type of >> >> global decls. That is, don't walk typeinfo decls - yes, practically >> >> that means just not walking DECL_ARTIFICIAL things. >> > Hi, >> > I have done the changes in the patch (attached) and cross-tested >> > on arm*-*-* and aarch64*-*-* without failures. >> > Is it OK for stage-1 ? >> Hi, >> Is the attached patch OK for trunk ? >> Bootstrapped and tested on aarch64-linux-gnu, ppc64le-linux-gnu. >> Cross-tested on arm*-*-* and aarch64*-*-*. > > You can't simply use > > + offset = int_byte_position (field); > > as it can be placed at variable offset which will make int_byte_position > ICE. Note it also returns a truncated byte position (bit position > stripped) which may be undesirable here. I think you want to use > bit_position and if and only if DECL_FIELD_OFFSET and > DECL_FIELD_BIT_OFFSET are INTEGER_CST. oops, I didn't realize offsets could be variable. Will that be the case only for VLA member inside struct ? > > Your observation about the expensiveness of the walk still stands I guess > and eventually you should at least cache the > get_vec_alignment_for_record_decl cases. Please make those workers > _type rather than _decl helpers. Done > > You seem to simply get at the maximum vectorized field/array element > alignment possible for all arrays - you could restrict that to > arrays with at least vector size (as followup). Um sorry, I didn't understand this part. > > + /* Skip artificial decls like typeinfo decls or if > + record is packed. */ > + if (DECL_ARTIFICIAL (record_decl) || TYPE_PACKED (type)) > + return 0; > > I think we should honor DECL_USER_ALIGN as well and not mess with those > decls. Done > > Given the patch now does quite some extra work it might make sense > to split the symtab part out of the vect_can_force_dr_alignment_p > predicate and call that early. In the patch I call symtab_node::can_increase_alignment_p early. I tried moving that to it's callers - vect_compute_data_ref_alignment and increase_alignment::execute, however that failed some tests in vect, and hence I didn't add the following hunk in the patch. Did I miss some check ? diff --git a/gcc/tree-vect-data-refs.c b/gcc/tree-vect-data-refs.c index 7652e21..2c1acee 100644 --- a/gcc/tree-vect-data-refs.c +++ b/gcc/tree-vect-data-refs.c @@ -795,7 +795,10 @@ vect_compute_data_ref_alignment (struct data_reference *dr) && TREE_CODE (TREE_OPERAND (base, 0)) == ADDR_EXPR) base = TREE_OPERAND (TREE_OPERAND (base, 0), 0); - if (!vect_can_force_dr_alignment_p (base, TYPE_ALIGN (vectype))) + if (!(TREE_CODE (base) == VAR_DECL + && decl_in_symtab_p (base) + && symtab_node::get (base)->can_increase_alignment_p () + && vect_can_force_dr_alignment_p (base, TYPE_ALIGN (vectype)))) { if (dump_enabled_p ()) { Thanks, Prathamesh > > Richard.
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