On Wed, 11 Oct 2023 at 16:57, Prathamesh Kulkarni
<[email protected]> wrote:
>
> On Wed, 11 Oct 2023 at 16:42, Prathamesh Kulkarni
> <[email protected]> wrote:
> >
> > On Mon, 9 Oct 2023 at 17:05, Richard Sandiford
> > <[email protected]> wrote:
> > >
> > > Prathamesh Kulkarni <[email protected]> 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)
+ {
+ 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))
+ {
+ 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" } } */
