> -----Original Message-----
> From: Richard Sandiford <richard.sandif...@arm.com>
> Sent: Friday, September 6, 2024 2:21 PM
> To: Tamar Christina <tamar.christ...@arm.com>
> Cc: gcc-patches@gcc.gnu.org; nd <n...@arm.com>
> Subject: Re: [PATCH 3/4][rtl]: simplify boolean vector EQ and NE comparisons
>
> Tamar Christina <tamar.christ...@arm.com> writes:
> > Hi All,
> >
> > This adds vector constant simplification for EQ and NE. This is useful
> > since
> > the vectorizer generates a lot more vector compares now, in particular NE
> > and EQ
> > and so these help us optimize cases where the values were not known at
> > GIMPLE
> > but instead only at RTL.
> >
> > Bootstrapped Regtested on aarch64-none-linux-gnu, arm-none-linux-gnueabihf,
> > x86_64-pc-linux-gnu -m32, -m64 and no issues.
> >
> > Ok for master?
> >
> > Thanks,
> > Tamar
> >
> > gcc/ChangeLog:
> >
> > * simplify-rtx.cc (simplify_context::simplify_unary_operation): Try
> > simplifying operand.
> > (simplify_const_relational_operation): Simplify vector EQ and NE.
> > (test_vector_int_const_compare): New.
> > (test_vector_int_const_compare_ops): New.
> > (simplify_rtx_cc_tests): Use them.
> >
> > ---
> >
> > diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc
> > index
> a20a61c5dddbc80b23a9489d925a2c31b2163458..7e83e80246b70c81c388e77
> 967f645d171efe983 100644
> > --- a/gcc/simplify-rtx.cc
> > +++ b/gcc/simplify-rtx.cc
> > @@ -886,6 +886,10 @@ simplify_context::simplify_unary_operation (rtx_code
> code, machine_mode mode,
> >
> > trueop = avoid_constant_pool_reference (op);
> >
> > + /* If the operand is not a reg or constant try simplifying it first. */
> > + if (rtx tmp_op = simplify_rtx (op))
> > + op = tmp_op;
> > +
>
> We shouldn't need to do this. The assumption is that the operands are
> already simplified.
>
> Which caller required this?
>
> > tem = simplify_const_unary_operation (code, mode, trueop, op_mode);
> > if (tem)
> > return tem;
> > @@ -6354,6 +6358,35 @@ simplify_const_relational_operation (enum rtx_code
> code,
> > return 0;
> > }
> >
> > + /* Check if the operands are a vector EQ or NE comparison. */
> > + if (VECTOR_MODE_P (mode)
> > + && INTEGRAL_MODE_P (mode)
> > + && GET_CODE (op0) == CONST_VECTOR
> > + && GET_CODE (op1) == CONST_VECTOR
> > + && (code == EQ || code == NE))
> > + {
> > + if (rtx_equal_p (op0, op1))
> > + return code == EQ ? const_true_rtx : const0_rtx;
> > +
> > + unsigned int npatterns0, npatterns1;
> > + if (CONST_VECTOR_NUNITS (op0).is_constant (&npatterns0)
> > + && CONST_VECTOR_NUNITS (op1).is_constant (&npatterns1))
> > + {
> > + if (npatterns0 != npatterns1)
> > + return code == EQ ? const0_rtx : const_true_rtx;
>
> This looks like a typing error. The operands have to have the same
> number of elements. But...
>
> > +
> > + for (unsigned i = 0; i < npatterns0; i++)
> > + {
> > + rtx val0 = CONST_VECTOR_ELT (op0, i);
> > + rtx val1 = CONST_VECTOR_ELT (op1, i);
> > + if (!rtx_equal_p (val0, val1))
> > + return code == EQ ? const0_rtx : const_true_rtx;
> > + }
> > +
> > + return code == EQ ? const_true_rtx : const0_rtx;
> > + }
>
> ...when is this loop needed? For constant-sized vectors, isn't the
> result always rtx_equal_p for EQ and !rtx_equal_p for NE? If we have
> equal vectors for which rtx_equal_p returns false then that should be
> fixed.
Hmm I suppose, I guess
if (rtx_equal_p (op0, op1))
return code == EQ ? const_true_rtx : const0_rtx;
else
return code == NE ? const_true_rtx : const0_rtx;
does the same thing,
Fair, I just didn't think about it ☹
>
> For variable-sized vectors, I suppose the question is whether the
> first unequal element is found in the minimum vector length, or whether
> it only occurs for larger lengths. In the former case we can fold at
> compile time, but in the latter case we can't.
>
> So we probably do want the loop for variable-length vectors, up to
> constant_lower_bound (CONST_VECTOR_NUNITS (...)).
>
> > + }
> > +
> > /* We can't simplify MODE_CC values since we don't know what the
> > actual comparison is. */
> > if (GET_MODE_CLASS (GET_MODE (op0)) == MODE_CC)
> > @@ -8820,6 +8853,55 @@ test_vector_ops ()
> > }
> > }
> >
> > +/* Verify vector constant comparisons for EQ and NE. */
> > +
> > +static void
> > +test_vector_int_const_compare (machine_mode mode)
> > +{
> > + rtx zeros = CONST0_RTX (mode);
> > + rtx minusone = CONSTM1_RTX (mode);
> > + rtx series_0_1 = gen_const_vec_series (mode, const0_rtx, const1_rtx);
> > + ASSERT_RTX_EQ (const0_rtx,
> > + simplify_const_relational_operation (EQ, mode, zeros,
> > + CONST1_RTX (mode)));
> > + ASSERT_RTX_EQ (const_true_rtx,
> > + simplify_const_relational_operation (EQ, mode, zeros,
> > + CONST0_RTX (mode)));
> > + ASSERT_RTX_EQ (const_true_rtx,
> > + simplify_const_relational_operation (EQ, mode, minusone,
> > + CONSTM1_RTX (mode)));
> > + ASSERT_RTX_EQ (const_true_rtx,
> > + simplify_const_relational_operation (NE, mode, zeros,
> > + CONST1_RTX (mode)));
> > + ASSERT_RTX_EQ (const_true_rtx,
> > + simplify_const_relational_operation (NE, mode, zeros,
> > + series_0_1));
> > + ASSERT_RTX_EQ (const0_rtx,
> > + simplify_const_relational_operation (EQ, mode, zeros,
> > + series_0_1));
> > +}
> > +
> > +/* Verify some simplifications involving vectors integer comparisons. */
> > +
> > +static void
> > +test_vector_int_const_compare_ops ()
> > +{
> > + for (unsigned int i = 0; i < NUM_MACHINE_MODES; ++i)
> > + {
> > + machine_mode mode = (machine_mode) i;
> > + if (VECTOR_MODE_P (mode)
> > + && INTEGRAL_MODE_P (mode)
> > + && GET_MODE_NUNITS (mode).is_constant ())
> > + {
> > + if (GET_MODE_CLASS (mode) == MODE_VECTOR_INT
> > + && maybe_gt (GET_MODE_NUNITS (mode), 2))
> > + {
> > + test_vector_int_const_compare (mode);
> > + }
> > + }
>
> If the above comments are right, we should be able to do this for
> variable-sized vectors as well.
Sure, will give it a try, thanks.
Cheers,
Tamar
>
> Thanks,
> Richard
>
> > + }
> > +}
> > +
> > template<unsigned int N>
> > struct simplify_const_poly_int_tests
> > {
> > @@ -8875,6 +8957,7 @@ simplify_rtx_cc_tests ()
> > {
> > test_scalar_ops ();
> > test_vector_ops ();
> > + test_vector_int_const_compare_ops ();
> > simplify_const_poly_int_tests<NUM_POLY_INT_COEFFS>::run ();
> > }
