[PATCH] simplify-rtx: Fix shortcut for vector eq/ne

[Richard Sandiford <richard.sandiford@arm.com>]

This patch forestalls a regression in gcc.dg/rtl/x86_64/vector_eq.c
with the patch for PR116398.  The test wants:

      (cinsn 3 (set (reg:V4SI <0>) (const_vector:V4SI [(const_int 0) (const_int 0) (const_int 0) (const_int 0)])))
      (cinsn 5 (set (reg:V4SI <2>)
		    (eq:V4SI (reg:V4SI <0>) (reg:V4SI <1>))))

to be folded to a vector of -1s.  One unusual thing about the fold
is that the <1> in the second insn is uninitialised; it looks like
it should be replaced by <0>, or that there should be an insn 4 that
copies <0> to <1>.

As it stands, the test relies on init-regs to insert a zero
initialisation of <1>.  This happens after all the cse/pre/fwprop
stuff, with only dce passes between init-regs and combine.
Combine therefore sees:

(insn 3 2 8 2 (set (reg:V4SI 98)
        (const_vector:V4SI [
                (const_int 0 [0]) repeated x4
            ])) 2403 {movv4si_internal}
     (nil))
(insn 8 3 9 2 (clobber (reg:V4SI 99)) -1
     (nil))
(insn 9 8 5 2 (set (reg:V4SI 99)
        (const_vector:V4SI [
                (const_int 0 [0]) repeated x4
            ])) -1
     (nil))
(insn 5 9 7 2 (set (reg:V4SI 100)
        (eq:V4SI (reg:V4SI 98)
            (reg:V4SI 99))) 7874 {*sse2_eqv4si3}
     (expr_list:REG_DEAD (reg:V4SI 99)
        (expr_list:REG_DEAD (reg:V4SI 98)
            (expr_list:REG_EQUAL (eq:V4SI (const_vector:V4SI [
                            (const_int 0 [0]) repeated x4
                        ])
                    (reg:V4SI 99))
                (nil)))))

It looks like the test should then pass through a 3, 9 -> 5 combination,
so that we get an (eq ...) between two zeros and fold it to a vector
of -1s.  But although the combination is attempted, the fold doesn't
happen.  Instead, combine is left to match the unsimplified (eq ...)
between two zeros, which rightly fails.  The test only passes because
late_combine2 happens to try simplifying an (eq ...) between reg X and
reg X, which does fold to a vector of -1s.

The different handling of registers and constants is due to this
code in simplify_const_relational_operation:

  if (INTEGRAL_MODE_P (mode) && trueop1 != const0_rtx
      && (code == EQ || code == NE)
      && ! ((REG_P (op0) || CONST_INT_P (trueop0))
	    && (REG_P (op1) || CONST_INT_P (trueop1)))
      && (tem = simplify_binary_operation (MINUS, mode, op0, op1)) != 0
      /* We cannot do this if tem is a nonzero address.  */
      && ! nonzero_address_p (tem))
    return simplify_const_relational_operation (signed_condition (code),
						mode, tem, const0_rtx);

INTEGRAL_MODE_P matches vector integer modes, but everything else
about the condition is written for scalar integers only.  Thus if
trueop0 and trueop1 are equal vector constants, we'll bypass all
the exclusions and try simplifying a subtraction.  This will succeed,
giving a vector of zeros.  The recursive call will then try to simplify
a comparison between the vector of zeros and const0_rtx, which isn't
well-formed.  Luckily or unluckily, the ill-formedness doesn't trigger
an ICE, but it does prevent any simplification from happening.

The least-effort fix would be to replace INTEGRAL_MODE_P with
SCALAR_INT_MODE_P.  But the fold does make conceptual sense for
vectors too, so it seemed better to keep the INTEGRAL_MODE_P and
generalise the rest of the condition to match.

Tested on aarch64-linux-gnu & x86_64-linux-gnu.  OK to install?

I'm hoping to post the actual patch for PR116398 later today.

Richard


gcc/
	* simplify-rtx.cc (simplify_const_relational_operation): Generalize
	the constant checks in the fold-via-minus path to match the
	INTEGRAL_MODE_P condition.
---
 gcc/simplify-rtx.cc | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc
index fe007bc7d96..6f969effdf9 100644
--- a/gcc/simplify-rtx.cc
+++ b/gcc/simplify-rtx.cc
@@ -6657,15 +6657,20 @@ simplify_const_relational_operation (enum rtx_code code,
      we do not know the signedness of the operation on either the left or
      the right hand side of the comparison.  */
 
-  if (INTEGRAL_MODE_P (mode) && trueop1 != const0_rtx
+  if (INTEGRAL_MODE_P (mode)
+      && trueop1 != CONST0_RTX (mode)
       && (code == EQ || code == NE)
-      && ! ((REG_P (op0) || CONST_INT_P (trueop0))
-	    && (REG_P (op1) || CONST_INT_P (trueop1)))
+      && ! ((REG_P (op0)
+	     || CONST_SCALAR_INT_P (trueop0)
+	     || CONST_VECTOR_P (trueop0))
+	    && (REG_P (op1)
+		|| CONST_SCALAR_INT_P (trueop1)
+		|| CONST_VECTOR_P (trueop1)))
       && (tem = simplify_binary_operation (MINUS, mode, op0, op1)) != 0
       /* We cannot do this if tem is a nonzero address.  */
       && ! nonzero_address_p (tem))
     return simplify_const_relational_operation (signed_condition (code),
-						mode, tem, const0_rtx);
+						mode, tem, CONST0_RTX (mode));
 
   if (! HONOR_NANS (mode) && code == ORDERED)
     return const_true_rtx;
-- 
2.25.1