On Mon, 9 Oct 2023 at 17:05, Richard Sandiford <richard.sandif...@arm.com> wrote: > > Prathamesh Kulkarni <prathamesh.kulka...@linaro.org> writes: > > Hi, > > The attached patch attempts to fix PR111648. > > As mentioned in PR, the issue is when a1 is a multiple of vector > > length, we end up creating following encoding in result: { base_elem, > > arg[0], arg[1], ... } (assuming S = 1), > > where arg is chosen input vector, which is incorrect, since the > > encoding originally in arg would be: { arg[0], arg[1], arg[2], ... } > > > > For the test-case mentioned in PR, vectorizer pass creates > > VEC_PERM_EXPR<arg0, arg, sel> where: > > arg0: { -16, -9, -10, -11 } > > arg1: { -12, -5, -6, -7 } > > sel = { 3, 4, 5, 6 } > > > > arg0, arg1 and sel are encoded with npatterns = 1 and nelts_per_pattern = 3. > > Since a1 = 4 and arg_len = 4, it ended up creating the result with > > following encoding: > > res = { arg0[3], arg1[0], arg1[1] } // npatterns = 1, nelts_per_pattern = 3 > > = { -11, -12, -5 } > > > > So for res[3], it used S = (-5) - (-12) = 7 > > And hence computed it as -5 + 7 = 2. > > instead of selecting arg1[2], ie, -6. > > > > The patch tweaks valid_mask_for_fold_vec_perm_cst_p to punt if a1 is a > > multiple > > of vector length, so a1 ... ae select elements only from stepped part > > of the pattern > > from input vector and return false for this case. > > > > Since the vectors are VLS, fold_vec_perm_cst then sets: > > res_npatterns = res_nelts > > res_nelts_per_pattern = 1 > > which seems to fix the issue by encoding all the elements. > > > > The patch resulted in Case 4 and Case 5 failing from test_nunits_min_2 > > because > > they used sel = { 0, 0, 1, ... } and {len, 0, 1, ... } respectively, > > which used a1 = 0, and thus selected arg1[0]. > > > > I removed Case 4 because it was already covered in test_nunits_min_4, > > and moved Case 5 to test_nunits_min_4, with sel = { len, 1, 2, ... } > > and added a new Case 9 to test for this issue. > > > > Passes bootstrap+test on aarch64-linux-gnu with and without SVE, > > and on x86_64-linux-gnu. > > Does the patch look OK ? > > > > Thanks, > > Prathamesh > > > > [PR111648] Fix wrong code-gen due to incorrect VEC_PERM_EXPR folding. > > > > gcc/ChangeLog: > > PR tree-optimization/111648 > > * fold-const.cc (valid_mask_for_fold_vec_perm_cst_p): Punt if a1 > > is a multiple of vector length. > > (test_nunits_min_2): Remove Case 4 and move Case 5 to ... > > (test_nunits_min_4): ... here and rename case numbers. Also add > > Case 9. > > > > gcc/testsuite/ChangeLog: > > PR tree-optimization/111648 > > * gcc.dg/vect/pr111648.c: New test. > > > > > > diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc > > index 4f8561509ff..c5f421d6b76 100644 > > --- a/gcc/fold-const.cc > > +++ b/gcc/fold-const.cc > > @@ -10682,8 +10682,8 @@ valid_mask_for_fold_vec_perm_cst_p (tree arg0, tree > > arg1, > > return false; > > } > > > > - /* Ensure that the stepped sequence always selects from the same > > - input pattern. */ > > + /* Ensure that the stepped sequence always selects from the stepped > > + part of same input pattern. */ > > unsigned arg_npatterns > > = ((q1 & 1) == 0) ? VECTOR_CST_NPATTERNS (arg0) > > : VECTOR_CST_NPATTERNS (arg1); > > @@ -10694,6 +10694,20 @@ valid_mask_for_fold_vec_perm_cst_p (tree arg0, > > tree arg1, > > *reason = "step is not multiple of npatterns"; > > return false; > > } > > + > > + /* If a1 is a multiple of len, it will select base element of input > > + vector resulting in following encoding: > > + { base_elem, arg[0], arg[1], ... } where arg is the chosen input > > + vector. This encoding is not originally present in arg, since it's > > + defined as: > > + { arg[0], arg[1], arg[2], ... }. */ > > + > > + if (multiple_p (a1, arg_len)) > > + { > > + if (reason) > > + *reason = "selecting base element of input vector"; > > + return false; > > + } > > That wouldn't catch (for example) cases where a1 == arg_len + 1 and the > second argument has 2 stepped patterns. Ah right, thanks for pointing out. In the attached patch I extended the check so that r1 < arg_npatterns which should check if we are choosing base elements from any of the patterns in arg (and not just first). Does that look OK ? > > The equivalent condition that handles multiple patterns would > probably be to reject q1 < arg_npatterns. But that's only necessary if: Sorry, I don't understand -- we use q1 only for determining which vector to choose from, and r1 will give the index for first element ? > > (1) the argument has three elements per pattern (i.e. has a stepped > sequence) and > > (2) element 2 - element 1 != element 1 - element 0 > > I think we should check those to avoid pessimising VLA cases. Thanks for the suggestions. In attached POC patch (stage-1 tested), I added the above checks, does it look in the right direction ? Also, should this patch be the right fix for PR111754 ?
Thanks, Prathamesh > > Thanks, > Richard > > > } > > > > return true; > > @@ -17425,47 +17439,6 @@ test_nunits_min_2 (machine_mode vmode) > > tree expected_res[] = { ARG0(0), ARG1(0), ARG0(1), ARG1(1) }; > > validate_res (2, 2, res, expected_res); > > } > > - > > - /* Case 4: mask = {0, 0, 1, ...} // (1, 3) > > - Test that the stepped sequence of the pattern selects from > > - same input pattern. Since input vectors have npatterns = 2, > > - and step (a2 - a1) = 1, step is not a multiple of npatterns > > - in input vector. So return NULL_TREE. */ > > - { > > - tree arg0 = build_vec_cst_rand (vmode, 2, 3, 1); > > - tree arg1 = build_vec_cst_rand (vmode, 2, 3, 1); > > - poly_uint64 len = TYPE_VECTOR_SUBPARTS (TREE_TYPE (arg0)); > > - > > - vec_perm_builder builder (len, 1, 3); > > - poly_uint64 mask_elems[] = { 0, 0, 1 }; > > - builder_push_elems (builder, mask_elems); > > - > > - vec_perm_indices sel (builder, 2, len); > > - const char *reason; > > - tree res = fold_vec_perm_cst (TREE_TYPE (arg0), arg0, arg1, sel, > > - &reason); > > - ASSERT_TRUE (res == NULL_TREE); > > - ASSERT_TRUE (!strcmp (reason, "step is not multiple of npatterns")); > > - } > > - > > - /* Case 5: mask = {len, 0, 1, ...} // (1, 3) > > - Test that stepped sequence of the pattern selects from arg0. > > - res = { arg1[0], arg0[0], arg0[1], ... } // (1, 3) */ > > - { > > - tree arg0 = build_vec_cst_rand (vmode, 1, 3, 1); > > - tree arg1 = build_vec_cst_rand (vmode, 1, 3, 1); > > - poly_uint64 len = TYPE_VECTOR_SUBPARTS (TREE_TYPE (arg0)); > > - > > - vec_perm_builder builder (len, 1, 3); > > - poly_uint64 mask_elems[] = { len, 0, 1 }; > > - builder_push_elems (builder, mask_elems); > > - > > - vec_perm_indices sel (builder, 2, len); > > - tree res = fold_vec_perm_cst (TREE_TYPE (arg0), arg0, arg1, sel); > > - > > - tree expected_res[] = { ARG1(0), ARG0(0), ARG0(1) }; > > - validate_res (1, 3, res, expected_res); > > - } > > } > > } > > > > @@ -17528,7 +17501,26 @@ test_nunits_min_4 (machine_mode vmode) > > validate_res (1, 3, res, expected_res); > > } > > > > - /* Case 4: > > + /* Case 4: mask = {len, 1, 2, ...} // (1, 3) > > + Test that stepped sequence of the pattern selects from arg0. > > + res = { arg1[0], arg0[1], arg0[2], ... } // (1, 3) */ > > + { > > + tree arg0 = build_vec_cst_rand (vmode, 1, 3, 1); > > + tree arg1 = build_vec_cst_rand (vmode, 1, 3, 1); > > + poly_uint64 len = TYPE_VECTOR_SUBPARTS (TREE_TYPE (arg0)); > > + > > + vec_perm_builder builder (len, 1, 3); > > + poly_uint64 mask_elems[] = { len, 1, 2 }; > > + builder_push_elems (builder, mask_elems); > > + > > + vec_perm_indices sel (builder, 2, len); > > + tree res = fold_vec_perm_cst (TREE_TYPE (arg0), arg0, arg1, sel); > > + > > + tree expected_res[] = { ARG1(0), ARG0(1), ARG0(2) }; > > + validate_res (1, 3, res, expected_res); > > + } > > + > > + /* Case 5: > > sel = { len, 0, 2, ... } // (1, 3) > > This should return NULL because we cross the input vectors. > > Because, > > @@ -17561,7 +17553,7 @@ test_nunits_min_4 (machine_mode vmode) > > ASSERT_TRUE (!strcmp (reason, "crossed input vectors")); > > } > > > > - /* Case 5: npatterns(arg0) = 4 > npatterns(sel) = 2 > > + /* Case 6: npatterns(arg0) = 4 > npatterns(sel) = 2 > > mask = { 0, len, 1, len + 1, ...} // (2, 2) > > res = { arg0[0], arg1[0], arg0[1], arg1[1], ... } // (2, 2) > > > > @@ -17583,7 +17575,7 @@ test_nunits_min_4 (machine_mode vmode) > > validate_res (2, 2, res, expected_res); > > } > > > > - /* Case 6: Test combination in sel, where one pattern is dup and > > other > > + /* Case 7: Test combination in sel, where one pattern is dup and > > other > > is stepped sequence. > > sel = { 0, 0, 0, 1, 0, 2, ... } // (2, 3) > > res = { arg0[0], arg0[0], arg0[0], > > @@ -17605,7 +17597,7 @@ test_nunits_min_4 (machine_mode vmode) > > validate_res (2, 3, res, expected_res); > > } > > > > - /* Case 7: PR111048: Check that we set arg_npatterns correctly, > > + /* Case 8: PR111048: Check that we set arg_npatterns correctly, > > when arg0, arg1 and sel have different number of patterns. > > arg0 is of shape (1, 1) > > arg1 is of shape (4, 1) > > @@ -17634,6 +17626,51 @@ test_nunits_min_4 (machine_mode vmode) > > ASSERT_TRUE (res == NULL_TREE); > > ASSERT_TRUE (!strcmp (reason, "step is not multiple of npatterns")); > > } > > + > > + /* Case 9: PR111648 - a1 is multiple of vector length, > > + which results in incorrect encoding. Verify that we return > > + NULL for this case. > > + sel = { base_elem, len, len+1, ... } // (1, 3) > > + In this case, the single pattern is: { base_elem len, len+1, ...} > > + Let's assume that base_elem is used for indexing into arg0, > > + and a1 ... ae chooses elements from arg1. > > + So res = { arg0[base_elem], arg1[0], arg1[1], ... } // (1, 3) > > + Which creates an incorrect encoding with S = arg1[1] - arg1[0] > > + while the original encoding in arg1 is > > + arg1: { arg1[0], arg1[1], arg1[2], ... } > > + with S = arg1[2] - arg1[1]. > > + > > + As a concrete example, for above PR: > > + arg0: { -16, -9, -10, -11 } > > + arg1: { -12, -5, -6, -7 } > > + sel = { 3, 4, 5, 6 } > > + > > + arg0, arg1 and sel are encoded with npatterns = 1 and > > nelts_per_pattern = 3. > > + Since a1 = 4 and arg_len = 4, it ended up creating the result with > > + following encoding: > > + res = { arg0[3], arg1[0], arg1[1] } // (1, 3) > > + = { -11, -12, -5 } > > + > > + So for res[3], it used S = (-5) - (-12) = 7 > > + And hence computed it as -5 + 7 = 2. > > + instead of arg1[2], ie, -6, which is the correct value. > > + Ensure that valid_mask_for_fold_vec_perm_cst returns false for this > > case. */ > > + { > > + tree arg0 = build_vec_cst_rand (vmode, 1, 3); > > + tree arg1 = build_vec_cst_rand (vmode, 1, 3); > > + poly_uint64 len = TYPE_VECTOR_SUBPARTS (TREE_TYPE (arg0)); > > + > > + vec_perm_builder builder (len, 1, 3); > > + poly_uint64 mask_elems[] = { 0, len, len+1 }; > > + builder_push_elems (builder, mask_elems); > > + > > + vec_perm_indices sel (builder, 2, len); > > + const char *reason; > > + tree res = fold_vec_perm_cst (TREE_TYPE (arg0), arg0, arg1, sel, > > &reason); > > + ASSERT_TRUE (res == NULL_TREE); > > + ASSERT_TRUE (!strcmp (reason, > > + "selecting base element of input vector")); > > + } > > } > > } > > > > diff --git a/gcc/testsuite/gcc.dg/vect/pr111648.c > > b/gcc/testsuite/gcc.dg/vect/pr111648.c > > new file mode 100644 > > index 00000000000..093e2b02654 > > --- /dev/null > > +++ b/gcc/testsuite/gcc.dg/vect/pr111648.c > > @@ -0,0 +1,23 @@ > > +/* { dg-do compile } */ > > +/* { dg-options "-O2 -fdump-tree-optimized" } */ > > + > > +int a; > > +int *b = &a; > > +static int **c = &b; > > +static int d; > > +short e; > > +short f; > > + > > +_Bool foo () > > +{ > > + f = -21; > > + for (; f < -5; f++) { > > + e = f ^ 3; > > + d = *b; > > + **c = e; > > + } > > + > > + return d == -6; > > +} > > + > > +/* { dg-final { scan-tree-dump "return 1" "optimized" } } */
diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc index 4f8561509ff..ae914cbd880 100644 --- a/gcc/fold-const.cc +++ b/gcc/fold-const.cc @@ -10607,6 +10607,25 @@ vec_cst_ctor_to_array (tree arg, unsigned int nelts, tree *elts) return true; } +static poly_int64 +vector_cst_elt_poly_index (tree arg, poly_uint64 index) +{ + int q; + poly_uint64 r; + poly_uint64 len = TYPE_VECTOR_SUBPARTS (TREE_TYPE (arg)); + + if (!can_div_trunc_p (index, len, &q, &r)) + return NULL_TREE; + + unsigned HOST_WIDE_INT i; + if (!r.is_constant (&i)) + return NULL_TREE; + + tree elem = vector_cst_elt (arg, i); + gcc_assert (elem != NULL_TREE); + return tree_to_poly_int64 (elem); +} + /* Helper routine for fold_vec_perm_cst to check if SEL is a suitable mask for VLA vec_perm folding. REASON if specified, will contain the reason why SEL is not suitable. @@ -10684,9 +10703,8 @@ valid_mask_for_fold_vec_perm_cst_p (tree arg0, tree arg1, /* Ensure that the stepped sequence always selects from the same input pattern. */ - unsigned arg_npatterns - = ((q1 & 1) == 0) ? VECTOR_CST_NPATTERNS (arg0) - : VECTOR_CST_NPATTERNS (arg1); + tree arg = ((q1 & 1) == 0) ? arg0 : arg1; + unsigned arg_npatterns = VECTOR_CST_NPATTERNS (arg); if (!multiple_p (step, arg_npatterns)) { @@ -10694,6 +10712,21 @@ valid_mask_for_fold_vec_perm_cst_p (tree arg0, tree arg1, *reason = "step is not multiple of npatterns"; return false; } + + /* Ensure that a1 only selects from stepped part of the pattern from arg, + if the pattern is not a natural stepped sequence, ie, + ((a2 - a1) != (a1 - a0)). */ + + poly_int64 arg_elem0 = vector_cst_elt_poly_index (arg, sel[pattern]); + poly_int64 arg_elem1 = vector_cst_elt_poly_index (arg, a1); + poly_int64 arg_elem2 = vector_cst_elt_poly_index (arg, a2); + if (!known_eq (arg_elem2 - arg_elem1, arg_elem1 - arg_elem0) + && known_lt (r1, arg_npatterns)) + { + if (reason) + *reason = "choosing base element from input vector"; + return false; + } } return true;