Prathamesh Kulkarni <prathamesh.kulka...@linaro.org> writes:
> On Wed, 11 Oct 2023 at 16:57, Prathamesh Kulkarni
> <prathamesh.kulka...@linaro.org> wrote:
>>
>> On Wed, 11 Oct 2023 at 16:42, Prathamesh Kulkarni
>> <prathamesh.kulka...@linaro.org> wrote:
>> >
>> > 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 ?
>> Oops sorry, this patch causes build errors on aarch64. Please ignore it.
>> Sorry for the noise.
> Hi Richard,
> The attached patch passes bootstrap+test on aarch64-linux-gnu with and
> without SVE,
> and on x86_64-linux-gnu.
> Does it look OK ?
>
> Thanks,
> Prathamesh
>>
>> Thanks,
>> Prathamesh
>> >
>> > 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..55a6a68c16c 100644
> --- a/gcc/fold-const.cc
> +++ b/gcc/fold-const.cc
> @@ -10684,9 +10684,8 @@ 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 +10693,29 @@ valid_mask_for_fold_vec_perm_cst_p (tree arg0, tree
> arg1,
> *reason = "step is not multiple of npatterns";
> return false;
> }
> +
> + /* If a1 chooses base element from arg, ensure that it's a natural
> + stepped sequence, ie, (arg[2] - arg[1]) == (arg[1] - arg[0])
> + to preserve arg's encoding. */
> +
> + unsigned HOST_WIDE_INT index;
> + if (!r1.is_constant (&index))
> + return false;
> + if (index < arg_npatterns)
> + {
I don't know whether it matters in practice, but I think the two conditions
above are more natural as:
if (maybe_lt (r1, arg_npatterns))
{
unsigned HOST_WIDE_INT index;
if (!r1.is_constant (&index))
return false;
...[code below]...
}
> + tree arg_elem0 = vector_cst_elt (arg, index);
> + tree arg_elem1 = vector_cst_elt (arg, index + arg_npatterns);
> + tree arg_elem2 = vector_cst_elt (arg, index + arg_npatterns * 2);
> +
> + if (!operand_equal_p (const_binop (MINUS_EXPR, arg_elem2, arg_elem1),
> + const_binop (MINUS_EXPR, arg_elem1, arg_elem0),
> + 0))
This needs to check whether const_binop returns null. Maybe:
tree step1, step2;
if (!(step1 = const_binop (MINUS_EXPR, arg_elem1, arg_elem0))
|| !(step2 = const_binop (MINUS_EXPR, arg_elem2, arg_elem1))
|| !operand_equal_p (step1, step2, 0))
OK with those changes, thanks.
Richard
> + {
> + if (reason)
> + *reason = "not a natural stepped sequence";
> + return false;
> + }
> + }
> }
>
> return true;
> @@ -17161,7 +17183,8 @@ namespace test_fold_vec_perm_cst {
> static tree
> build_vec_cst_rand (machine_mode vmode, unsigned npatterns,
> unsigned nelts_per_pattern,
> - int step = 0, int threshold = 100)
> + int step = 0, bool natural_stepped = false,
> + int threshold = 100)
> {
> tree inner_type = lang_hooks.types.type_for_mode (GET_MODE_INNER (vmode),
> 1);
> tree vectype = build_vector_type_for_mode (inner_type, vmode);
> @@ -17176,17 +17199,28 @@ build_vec_cst_rand (machine_mode vmode, unsigned
> npatterns,
>
> // Fill a1 for each pattern
> for (unsigned i = 0; i < npatterns; i++)
> - builder.quick_push (build_int_cst (inner_type, rand () % threshold));
> -
> + {
> + tree a1;
> + if (natural_stepped)
> + {
> + tree a0 = builder[i];
> + wide_int a0_val = wi::to_wide (a0);
> + wide_int a1_val = a0_val + step;
> + a1 = wide_int_to_tree (inner_type, a1_val);
> + }
> + else
> + a1 = build_int_cst (inner_type, rand () % threshold);
> + builder.quick_push (a1);
> + }
> if (nelts_per_pattern == 2)
> return builder.build ();
>
> for (unsigned i = npatterns * 2; i < npatterns * nelts_per_pattern; i++)
> {
> tree prev_elem = builder[i - npatterns];
> - int prev_elem_val = TREE_INT_CST_LOW (prev_elem);
> - int val = prev_elem_val + step;
> - builder.quick_push (build_int_cst (inner_type, val));
> + wide_int prev_elem_val = wi::to_wide (prev_elem);
> + wide_int val = prev_elem_val + step;
> + builder.quick_push (wide_int_to_tree (inner_type, val));
> }
>
> return builder.build ();
> @@ -17432,7 +17466,7 @@ test_nunits_min_2 (machine_mode vmode)
> 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 arg0 = build_vec_cst_rand (vmode, 2, 3, 1, true);
> tree arg1 = build_vec_cst_rand (vmode, 2, 3, 1);
> poly_uint64 len = TYPE_VECTOR_SUBPARTS (TREE_TYPE (arg0));
>
> @@ -17452,7 +17486,7 @@ test_nunits_min_2 (machine_mode vmode)
> 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 arg0 = build_vec_cst_rand (vmode, 1, 3, 1, true);
> tree arg1 = build_vec_cst_rand (vmode, 1, 3, 1);
> poly_uint64 len = TYPE_VECTOR_SUBPARTS (TREE_TYPE (arg0));
>
> @@ -17466,6 +17500,62 @@ test_nunits_min_2 (machine_mode vmode)
> tree expected_res[] = { ARG1(0), ARG0(0), ARG0(1) };
> validate_res (1, 3, res, expected_res);
> }
> +
> + /* Case 6: PR111648 - a1 chooses base element from input vector arg.
> + In this case ensure that arg has a natural stepped sequence
> + to preserve arg's encoding.
> +
> + As a concrete example, consider:
> + arg0: { -16, -9, -10, ... } // (1, 3)
> + arg1: { -12, -5, -6, ... } // (1, 3)
> + sel = { 0, len, len + 1, ... } // (1, 3)
> +
> + This will create res with following encoding:
> + res = { arg0[0], arg1[0], arg1[1], ... } // (1, 3)
> + = { -16, -12, -5, ... }
> +
> + The step in above encoding would be: (-5) - (-12) = 7
> + And hence res[3] would be computed as -5 + 7 = 2.
> + instead of arg1[2], ie, -6.
> + Ensure that valid_mask_for_fold_vec_perm_cst returns false
> + for this case. */
> + {
> + 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[] = { 0, len, len+1 };
> + builder_push_elems (builder, mask_elems);
> +
> + vec_perm_indices sel (builder, 2, len);
> + const char *reason;
> + /* FIXME: It may happen that build_vec_cst_rand may build a natural
> + stepped pattern, even if we didn't explicitly tell it to. So folding
> + may not always fail, but if it does, ensure that's because arg1 does
> + not have a natural stepped sequence (and not due to other reason) */
> + tree res = fold_vec_perm_cst (TREE_TYPE (arg0), arg0, arg1, sel,
> &reason);
> + if (res == NULL_TREE)
> + ASSERT_TRUE (!strcmp (reason, "not a natural stepped sequence"));
> + }
> +
> + /* Case 7: Same as Case 6, except that arg1 contains natural stepped
> + sequence and thus folding should be valid for this case. */
> + {
> + tree arg0 = build_vec_cst_rand (vmode, 1, 3, 1);
> + tree arg1 = build_vec_cst_rand (vmode, 1, 3, 1, true);
> + 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);
> + tree res = fold_vec_perm_cst (TREE_TYPE (arg0), arg0, arg1, sel);
> +
> + tree expected_res[] = { ARG0(0), ARG1(0), ARG1(1) };
> + validate_res (1, 3, res, expected_res);
> + }
> }
> }
>
> 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" } } */
