On Thu, 3 Aug 2023 at 18:46, Richard Sandiford wrote: > > Richard Sandiford writes: > > Prathamesh Kulkarni writes: > >> On Tue, 25 Jul 2023 at 18:25, Richard Sandiford > >> wrote: > >>> > >>> Hi, > >>> > >>> Thanks for the rework and sorry for the slow review. > >> Hi Richard, > >> Thanks for the suggestions! Please find my responses inline below. > >>> > >>> Prathamesh Kulkarni writes: > >>> > Hi Richard, > >>> > This is reworking of patch to extend fold_vec_perm to handle VLA vectors. > >>> > The attached patch unifies handling of VLS and VLA vector_csts, while > >>> > using fallback code > >>> > for ctors. > >>> > > >>> > For VLS vector, the patch ignores underlying encoding, and > >>> > uses npatterns = nelts, and nelts_per_pattern = 1. > >>> > > >>> > For VLA patterns, if sel has a stepped sequence, then it > >>> > only chooses elements from a particular pattern of a particular > >>> > input vector. > >>> > > >>> > To make things simpler, the patch imposes following constraints: > >>> > (a) op0_npatterns, op1_npatterns and sel_npatterns are powers of 2. > >>> > (b) The step size for a stepped sequence is a power of 2, and > >>> > multiple of npatterns of chosen input vector. > >>> > (c) Runtime vector length of sel is a multiple of sel_npatterns. > >>> > So, we don't handle sel.length = 2 + 2x and npatterns = 4. > >>> > > >>> > Eg: > >>> > op0, op1: npatterns = 2, nelts_per_pattern = 3 > >>> > op0_len = op1_len = 16 + 16x. > >>> > sel = { 0, 0, 2, 0, 4, 0, ... } > >>> > npatterns = 2, nelts_per_pattern = 3. > >>> > > >>> > For pattern {0, 2, 4, ...} > >>> > Let, > >>> > a1 = 2 > >>> > S = step size = 2 > >>> > > >>> > Let Esel denote number of elements per pattern in sel at runtime. > >>> > Esel = (16 + 16x) / npatterns_sel > >>> > = (16 + 16x) / 2 > >>> > = (8 + 8x) > >>> > > >>> > So, last element of pattern: > >>> > ae = a1 + (Esel - 2) * S > >>> > = 2 + (8 + 8x - 2) * 2 > >>> > = 14 + 16x > >>> > > >>> > a1 /trunc arg0_len = 2 / (16 + 16x) = 0 > >>> > ae /trunc arg0_len = (14 + 16x) / (16 + 16x) = 0 > >>> > Since both are equal with quotient = 0, we select elements from op0. > >>> > > >>> > Since step size (S) is a multiple of npatterns(op0), we select > >>> > all elements from same pattern of op0. > >>> > > >>> > res_npatterns = max (op0_npatterns, max (op1_npatterns, sel_npatterns)) > >>> > = max (2, max (2, 2) > >>> > = 2 > >>> > > >>> > res_nelts_per_pattern = max (op0_nelts_per_pattern, > >>> > max (op1_nelts_per_pattern, > >>> > sel_nelts_per_pattern)) > >>> > = max (3, max (3, 3)) > >>> > = 3 > >>> > > >>> > So res has encoding with npatterns = 2, nelts_per_pattern = 3. > >>> > res: { op0[0], op0[0], op0[2], op0[0], op0[4], op0[0], ... } > >>> > > >>> > Unfortunately, this results in an issue for poly_int_cst index: > >>> > For example, > >>> > op0, op1: npatterns = 1, nelts_per_pattern = 3 > >>> > op0_len = op1_len = 4 + 4x > >>> > > >>> > sel: { 4 + 4x, 5 + 4x, 6 + 4x, ... } // should choose op1 > >>> > > >>> > In this case, > >>> > a1 = 5 + 4x > >>> > S = (6 + 4x) - (5 + 4x) = 1 > >>> > Esel = 4 + 4x > >>> > > >>> > ae = a1 + (esel - 2) * S > >>> > = (5 + 4x) + (4 + 4x - 2) * 1 > >>> > = 7 + 8x > >>> > > >>> > IIUC, 7 + 8x will always be index for last element of op1 ? > >>> > if x = 0, len = 4, 7 + 8x = 7 > >>> > if x = 1, len = 8, 7 + 8x = 15, etc. > >>> > So the stepped sequence will always choose elements > >>> > from op1 regardless of vector length for above case ? > >>> > > >>> > However, > >>> > ae /trunc op0_len > >>> > = (7 + 8x) / (4 + 4x) > >>> > which is not defined because 7/4 != 8/4 > >>> > and we return NULL_TREE, but I suppose the expected result would be: > >>> > res: { op1[0], op1[1], op1[2], ... } ? > >>> > > >>> > The patch passes bootstrap+test on aarch64-linux-gnu with and without sve, > >>> > and on x86_64-unknown-linux-gnu. > >>> > I would be grateful for suggestions on how to proceed. > >>> > > >>> > Thanks, > >>> > Prathamesh > >>> > > >>> > diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc > >>> > index a02ede79fed..8028b3e8e9a 100644 > >>> > --- a/gcc/fold-const.cc > >>> > +++ b/gcc/fold-const.cc > >>> > @@ -85,6 +85,10 @@ along with GCC; see the file COPYING3. If not see > >>> > #include "vec-perm-indices.h" > >>> > #include "asan.h" > >>> > #include "gimple-range.h" > >>> > +#include > >>> > +#include "tree-pretty-print.h" > >>> > +#include "gimple-pretty-print.h" > >>> > +#include "print-tree.h" > >>> > > >>> > /* Nonzero if we are folding constants inside an initializer or a C++ > >>> > manifestly-constant-evaluated context; zero otherwise. > >>> > @@ -10493,15 +10497,9 @@ fold_mult_zconjz (location_t loc, tree type, tree expr) > >>> > static bool > >>> > vec_cst_ctor_to_array (tree arg, unsigned int nelts, tree *elts) > >>> > { > >>> > - unsigned HOST_WIDE_INT i, nunits; > >>> > + unsigned HOST_WIDE_INT i; > >>> > > >>> > - if (TREE_CODE (arg) == VECTOR_CST > >>> > - && VECTOR_CST_NELTS (arg).is_constant (&nunits)) > >>> > - { > >>> > - for (i = 0; i < nunits; ++i) > >>> > - elts[i] = VECTOR_CST_ELT (arg, i); > >>> > - } > >>> > - else if (TREE_CODE (arg) == CONSTRUCTOR) > >>> > + if (TREE_CODE (arg) == CONSTRUCTOR) > >>> > { > >>> > constructor_elt *elt; > >>> > > >>> > @@ -10519,6 +10517,230 @@ vec_cst_ctor_to_array (tree arg, unsigned int nelts, tree *elts) > >>> > return true; > >>> > } > >>> > > >>> > +/* Return a vector with (NPATTERNS, NELTS_PER_PATTERN) encoding. */ > >>> > + > >>> > +static tree > >>> > +vector_cst_reshape (tree vec, unsigned npatterns, unsigned nelts_per_pattern) > >>> > +{ > >>> > + gcc_assert (pow2p_hwi (npatterns)); > >>> > + > >>> > + if (VECTOR_CST_NPATTERNS (vec) == npatterns > >>> > + && VECTOR_CST_NELTS_PER_PATTERN (vec) == nelts_per_pattern) > >>> > + return vec; > >>> > + > >>> > + tree v = make_vector (exact_log2 (npatterns), nelts_per_pattern); > >>> > + TREE_TYPE (v) = TREE_TYPE (vec); > >>> > + > >>> > + unsigned nelts = npatterns * nelts_per_pattern; > >>> > + for (unsigned i = 0; i < nelts; i++) > >>> > + VECTOR_CST_ENCODED_ELT(v, i) = vector_cst_elt (vec, i); > >>> > + return v; > >>> > +} > >>> > + > >>> > +/* Helper routine for fold_vec_perm_vla to check if ARG is a suitable > >>> > + operand for VLA vec_perm folding. If arg is VLS, then set > >>> > + NPATTERNS = nelts and NELTS_PER_PATTERN = 1. */ > >>> > + > >>> > +static tree > >>> > +valid_operand_for_fold_vec_perm_cst_p (tree arg) > >>> > +{ > >>> > + if (TREE_CODE (arg) != VECTOR_CST) > >>> > + return NULL_TREE; > >>> > + > >>> > + unsigned HOST_WIDE_INT nelts; > >>> > + unsigned npatterns, nelts_per_pattern; > >>> > + if (TYPE_VECTOR_SUBPARTS (TREE_TYPE (arg)).is_constant (&nelts)) > >>> > + { > >>> > + npatterns = nelts; > >>> > + nelts_per_pattern = 1; > >>> > + } > >>> > + else > >>> > + { > >>> > + npatterns = VECTOR_CST_NPATTERNS (arg); > >>> > + nelts_per_pattern = VECTOR_CST_NELTS_PER_PATTERN (arg); > >>> > + } > >>> > + > >>> > + if (!pow2p_hwi (npatterns)) > >>> > + return NULL_TREE; > >>> > + > >>> > + return vector_cst_reshape (arg, npatterns, nelts_per_pattern); > >>> > +} > >>> > >>> I don't think we should reshape the vectors for VLS, since it would > >>> create more nodes for GC to clean up later. Also, the "compact" encoding > >>> is canonical even for VLS, so the reshaping would effectively create > >>> noncanonical constants (even if only temporarily). > >> Removed in the attached patch. > >>> > >>> Instead, I think we should change the later: > >>> > >>> > + if (!valid_mask_for_fold_vec_perm_cst_p (arg0, arg1, sel, sel_npatterns, > >>> > + sel_nelts_per_pattern, reason, verbose)) > >>> > + return NULL_TREE; > >>> > >>> so that it comes after the computation of res_npatterns and > >>> res_nelts_per_pattern. Then, if valid_mask_for_fold_vec_perm_cst_p > >>> returns false, and if the result type has a constant number of elements, > >>> we should: > >>> > >>> * set res_npatterns to that number of elements > >>> * set res_nelts_per_pattern to 1 > >>> * continue instead of returning null > >> Assuming we don't enforce only VLA or only VLS for input vectors and sel, > >> won't that be still an issue if res (and sel) is VLS, and input > >> vectors are VLA ? > >> For eg: > >> arg0, arg1 are type VNx4SI with npatterns = 2, nelts_per_pattern = 3, step = 2 > >> sel is V4SI constant with encoding { 0, 2, 4, ... } > >> and res_type is V4SI. > >> In this case, when it comes to index 4, the vector selection becomes ambiguous, > >> since it can be arg1 for len = 4 + 4x, and arg0 for lengths > 4 + 4x ? > > > > Ah, right. So the condition is whether the result type and the data > > input type have a constant number of elements, rather than just the result. > > Actually, I take that back. The reason: > > >>> The loop that follows will then do the correct thing for each element. > > is true is that: > > + if (!can_div_trunc_p (sel[i], len, &q, &r)) > + { > + if (reason) > + strcpy (reason, "cannot divide selector element by arg len"); > + return NULL_TREE; > + } > > will return false if q isn't computable at compile time (that is, > if we can't decide at compile time which input the element comes from). > > So I think checking the result is enough. Ah yes, thanks for pointing it out! I verified that's indeed the case (test 4 in test_fold_vec_perm_cst::test_mixed in attached patch). Does the attached patch look OK ? Bootstrapped+tested on aarch64-linux-gnu with and without SVE, and on x86_64-linux-gnu. Thanks, Prathamesh > > Thanks, > Richard