On Wed, 19 Jul 2023, Jakub Jelinek wrote:
> On Tue, Jul 18, 2023 at 01:25:45PM +0200, Richard Biener wrote:
> >
> > PR middle-end/61747
> > * internal-fn.cc (expand_vec_cond_optab_fn): When the
> > value operands are equal to the original comparison operands
> > preserve that equality by re-using the comparison expansion.
> > * optabs.cc (emit_conditional_move): When the value operands
> > are equal to the comparison operands and would be forced to
> > a register by prepare_cmp_insn do so earlier, preserving the
> > equality.
> >
> > * g++.target/i386/pr61747.C: New testcase.
> > ---
> > gcc/internal-fn.cc | 17 ++++++++--
> > gcc/optabs.cc | 32 ++++++++++++++++++-
> > gcc/testsuite/g++.target/i386/pr61747.C | 42 +++++++++++++++++++++++++
> > 3 files changed, 88 insertions(+), 3 deletions(-)
> > create mode 100644 gcc/testsuite/g++.target/i386/pr61747.C
> >
> > diff --git a/gcc/internal-fn.cc b/gcc/internal-fn.cc
> > index e698f0bffc7..c83c3921792 100644
> > --- a/gcc/internal-fn.cc
> > +++ b/gcc/internal-fn.cc
> > @@ -3019,8 +3019,21 @@ expand_vec_cond_optab_fn (internal_fn, gcall *stmt,
> > convert_optab optab)
> > icode = convert_optab_handler (optab, mode, cmp_op_mode);
> > rtx comparison
> > = vector_compare_rtx (VOIDmode, tcode, op0a, op0b, unsignedp, icode,
> > 4);
> > - rtx rtx_op1 = expand_normal (op1);
> > - rtx rtx_op2 = expand_normal (op2);
> > + /* vector_compare_rtx legitimizes operands, preserve equality when
> > + expanding op1/op2. */
> > + rtx rtx_op1, rtx_op2;
> > + if (operand_equal_p (op1, op0a))
> > + rtx_op1 = XEXP (comparison, 0);
> > + else if (operand_equal_p (op1, op0b))
> > + rtx_op1 = XEXP (comparison, 1);
> > + else
> > + rtx_op1 = expand_normal (op1);
> > + if (operand_equal_p (op2, op0a))
> > + rtx_op2 = XEXP (comparison, 0);
> > + else if (operand_equal_p (op2, op0b))
> > + rtx_op2 = XEXP (comparison, 1);
> > + else
> > + rtx_op2 = expand_normal (op2);
> >
> > rtx target = expand_expr (lhs, NULL_RTX, VOIDmode, EXPAND_WRITE);
> > create_output_operand (&ops[0], target, mode);
>
> The above LGTM, it relies on vector_compare_rtx not swapping the arguments
> or performing some other comparison canonicalization, but at least right now
> that function doesn't seem to do that.
>
> > --- a/gcc/optabs.cc
> > +++ b/gcc/optabs.cc
> > @@ -5119,13 +5119,43 @@ emit_conditional_move (rtx target, struct
> > rtx_comparison comp,
> > last = get_last_insn ();
> > do_pending_stack_adjust ();
> > machine_mode cmpmode = comp.mode;
> > + rtx orig_op0 = XEXP (comparison, 0);
> > + rtx orig_op1 = XEXP (comparison, 1);
> > + rtx op2p = op2;
> > + rtx op3p = op3;
> > + /* If we are optimizing, force expensive constants into a register
> > + but preserve an eventual equality with op2/op3. */
> > + if (CONSTANT_P (orig_op0) && optimize
> > + && (rtx_cost (orig_op0, mode, COMPARE, 0,
> > + optimize_insn_for_speed_p ())
> > + > COSTS_N_INSNS (1))
> > + && can_create_pseudo_p ())
> > + {
> > + XEXP (comparison, 0) = force_reg (cmpmode, orig_op0);
> > + if (rtx_equal_p (orig_op0, op2))
> > + op2p = XEXP (comparison, 0);
> > + if (rtx_equal_p (orig_op0, op3))
> > + op3p = XEXP (comparison, 0);
> > + }
> > + if (CONSTANT_P (orig_op1) && optimize
> > + && (rtx_cost (orig_op1, mode, COMPARE, 0,
> > + optimize_insn_for_speed_p ())
> > + > COSTS_N_INSNS (1))
> > + && can_create_pseudo_p ())
> > + {
> > + XEXP (comparison, 1) = force_reg (cmpmode, orig_op1);
> > + if (rtx_equal_p (orig_op1, op2))
> > + op2p = XEXP (comparison, 1);
> > + if (rtx_equal_p (orig_op1, op3))
> > + op3p = XEXP (comparison, 1);
> > + }
>
> I'm worried here, because prepare_cmp_insn before doing almost identical
> forcing to reg does
> if (CONST_SCALAR_INT_P (y))
> canonicalize_comparison (mode, &comparison, &y);
> which the above change will make not happen anymore (for the more expensive
> constants).
Hmm, yeah - that could happen.
> If we have a match between at least one of the comparison operands and
> op2/op3, I think having equivalency there is perhaps more important than
> the canonicalization, but it would be nice not to break it even if there
> is no match. So, perhaps force_reg only if there is a match?
> force_reg (cmpmode, force_reg (cmpmode, x)) is equivalent to
> force_reg (cmpmode, x), so perhaps:
> {
> if (rtx_equal_p (orig_op0, op2))
> op2p = XEXP (comparison, 0) = force_reg (cmpmode, orig_op0);
> if (rtx_equal_p (orig_op0, op3))
> op3p = XEXP (comparison, 0)
> = force_reg (cmpmode, XEXP (comparison, 0));
> }
> and similarly for the other body?
I don't think we'll have op3 == op2 == orig_op0 because if
op2 == op3 the
/* If the two source operands are identical, that's just a move. */
if (rtx_equal_p (op2, op3))
{
if (!target)
target = gen_reg_rtx (mode);
emit_move_insn (target, op3);
return target;
code should have triggered. So we should know we invoke force_reg
only once for each comparison operand check?
So I'm going to test the following ontop of the patch.
Thanks,
Richard.
diff --git a/gcc/optabs.cc b/gcc/optabs.cc
index a9ba3267666..2ac4b2698b2 100644
--- a/gcc/optabs.cc
+++ b/gcc/optabs.cc
@@ -5131,11 +5131,10 @@ emit_conditional_move (rtx target, struct
rtx_comparison comp,
> COSTS_N_INSNS (1))
&& can_create_pseudo_p ())
{
- XEXP (comparison, 0) = force_reg (cmpmode, orig_op0);
if (rtx_equal_p (orig_op0, op2))
- op2p = XEXP (comparison, 0);
+ op2p = XEXP (comparison, 0) = force_reg (cmpmode,
orig_op0);
if (rtx_equal_p (orig_op0, op3))
- op3p = XEXP (comparison, 0);
+ op3p = XEXP (comparison, 0) = force_reg (cmpmode,
orig_op0);
}
if (CONSTANT_P (orig_op1) && optimize
&& (rtx_cost (orig_op1, mode, COMPARE, 0,
@@ -5143,11 +5142,10 @@ emit_conditional_move (rtx target, struct
rtx_comparison comp,
> COSTS_N_INSNS (1))
&& can_create_pseudo_p ())
{
- XEXP (comparison, 1) = force_reg (cmpmode, orig_op1);
if (rtx_equal_p (orig_op1, op2))
- op2p = XEXP (comparison, 1);
+ op2p = XEXP (comparison, 1) = force_reg (cmpmode,
orig_op1);
if (rtx_equal_p (orig_op1, op3))
- op3p = XEXP (comparison, 1);
+ op3p = XEXP (comparison, 1) = force_reg (cmpmode,
orig_op1);
}
prepare_cmp_insn (XEXP (comparison, 0), XEXP (comparison, 1),
GET_CODE (comparison), NULL_RTX, unsignedp,
