The following fixes a regression in AVX2 vectorization because on
trunk we are now correctly determine we can shorten a shift operation
but we never really bothered to check we can implement the
resulting operation. With the patch we now check this. For shifts
and rotates we have the choice between vector-vector and vector-scalar
operations which in the end depends on whether we perform SLP or not
and how the shift operand matches up. The patch heuristically
assumes that constant or external shifts can be handled by vector-scalar
operations.
ISTR not checking for target support was to allow recursive matching
other patterns, but as can be seen here this is problematic.
Bootstrapping/testing on x86_64-unknown-linux-gnu and aarch64-linux
reveals
+FAIL: gcc.dg/vect/vect-over-widen-13.c -flto -ffat-lto-objects
scan-tree-dump-
not vect "vector[^ ]* int"
on both and
+FAIL: gcc.dg/vect/vect-div-bitmask-1.c -flto -ffat-lto-objects
scan-tree-dump-not vect "vect_recog_divmod_pattern: detected"
on aarch64 (might be old baseline).
So how was this supposed to play out? Do we need to handle
pattern composition in other ways?
Thanks,
Richard.
PR tree-optimization/124068
* tree-vect-patterns.cc (target_has_vecop_for_code): Move
earlier, add defaulted optab_subtype parameter.
(vect_recog_over_widening_pattern): Check that the target
supports the narrowed operation before committing to the
pattern.
* gcc.target/i386/vect-shift-1.c: New testcase.
---
gcc/testsuite/gcc.target/i386/vect-shift-1.c | 10 ++++++
gcc/tree-vect-patterns.cc | 36 ++++++++++++++------
2 files changed, 35 insertions(+), 11 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/i386/vect-shift-1.c
diff --git a/gcc/testsuite/gcc.target/i386/vect-shift-1.c
b/gcc/testsuite/gcc.target/i386/vect-shift-1.c
new file mode 100644
index 00000000000..eb31ef48ba0
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/vect-shift-1.c
@@ -0,0 +1,10 @@
+/* { dg-do compile { target avx2 } } */
+/* { dg-options "-O2 -mavx2 -mno-avx512f -fdump-tree-vect-details" } */
+
+void f (short* acc)
+{
+ for (unsigned char row = 0; row < 16; ++row)
+ acc[row] = acc[row] << row;
+}
+
+/* { dg-final { scan-tree-dump "optimized: loop vectorized" "vect" } } */
diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
index 11004043aca..b8a0af323ba 100644
--- a/gcc/tree-vect-patterns.cc
+++ b/gcc/tree-vect-patterns.cc
@@ -1036,6 +1036,17 @@ vect_reassociating_reduction_p (vec_info *vinfo,
return true;
}
+/* Return true iff the target has a vector optab implementing the operation
+ CODE on type VECTYPE with SUBTYPE. */
+
+static bool
+target_has_vecop_for_code (tree_code code, tree vectype,
+ enum optab_subtype subtype = optab_vector)
+{
+ optab voptab = optab_for_tree_code (code, vectype, subtype);
+ return voptab && can_implement_p (voptab, TYPE_MODE (vectype));
+}
+
/* match.pd function to match
(cond (cmp@3 a b) (convert@1 c) (convert@2 d))
with conditions:
@@ -3170,6 +3181,20 @@ vect_recog_over_widening_pattern (vec_info *vinfo,
if (!new_vectype || !op_vectype)
return NULL;
+ /* Verify we can handle the new operation. For shifts and rotates
+ apply heuristic of whether we are likely facing vector-vector or
+ vector-scalar operation. */
+ if (code == RSHIFT_EXPR || code == LSHIFT_EXPR || code == RROTATE_EXPR)
+ {
+ if (!target_has_vecop_for_code (code, op_vectype, optab_vector)
+ && ((unprom[1].dt != vect_external_def
+ && unprom[1].dt != vect_constant_def)
+ || !target_has_vecop_for_code (code, op_vectype, optab_scalar)))
+ return NULL;
+ }
+ else if (!target_has_vecop_for_code (code, op_vectype, optab_vector))
+ return NULL;
+
if (dump_enabled_p ())
dump_printf_loc (MSG_NOTE, vect_location, "demoting %T to %T\n",
type, new_type);
@@ -4151,17 +4176,6 @@ vect_recog_vector_vector_shift_pattern (vec_info *vinfo,
return pattern_stmt;
}
-/* Return true iff the target has a vector optab implementing the operation
- CODE on type VECTYPE. */
-
-static bool
-target_has_vecop_for_code (tree_code code, tree vectype)
-{
- optab voptab = optab_for_tree_code (code, vectype, optab_vector);
- return voptab
- && can_implement_p (voptab, TYPE_MODE (vectype));
-}
-
/* Verify that the target has optabs of VECTYPE to perform all the steps
needed by the multiplication-by-immediate synthesis algorithm described by
ALG and VAR. If SYNTH_SHIFT_P is true ensure that vector addition is
--
2.51.0
