i386: Fix up avx_vpermilp_parallel [PR124138]

r16-3677 extended avx_vpermilp_parallel so that it handles also V8DImode
(among others) and broke this testcase.
For V8DFmode the bug existed there already since r0-127405 which extended
avx_vpermilp_parallel to handle V8DFmode.
For V16SImode/V16SFmode I think the code is correct, in that case it can
for V4SImode/V4SFmode choose any permutation it wants and the
V8S{I,F}mode and V16S{I,F}mode cases before FALLTHRU verify the upper lanes
match those lower ones.
For V[48]D[IF]mode the function uses different checking, where it checks
each pair of ipar separately:
    case E_V8DFmode:
    case E_V8DImode:
      /* In the 512-bit DFmode case, we can only move elements within
         a 128-bit lane.  First fill the second part of the mask,
         then fallthru.  */
      for (i = 4; i < 6; ++i)
        {
          if (ipar[i] < 4 || ipar[i] >= 6)
            return 0;
          mask |= (ipar[i] - 4) << i;
        }
      for (i = 6; i < 8; ++i)
        {
          if (ipar[i] < 6)
            return 0;
          mask |= (ipar[i] - 6) << i;
        }
      /* FALLTHRU */

    case E_V4DFmode:
    case E_V4DImode:
      /* In the 256-bit DFmode case, we can only move elements within
         a 128-bit lane.  */
      for (i = 0; i < 2; ++i)
        {
          if (ipar[i] >= 2)
            return 0;
          mask |= ipar[i] << i;
        }
      for (i = 2; i < 4; ++i)
        {
          if (ipar[i] < 2)
            return 0;
          mask |= (ipar[i] - 2) << i;
        }
      break;
so that it directly computes corresponding mask bit.
Earlier in the function it verified ipar[i] wasn't above
nelts (nor negative), so just checking if (ipar[i] >= 2) is ok, it can't
be negative, and just checking if (ipar[i] < 6) is also fine, because
it can never be 8 or above (because nelts is 8 in that case).
Though, the if (ipar[i] < 2) case check used to be correct only when
nelts could be only 4, when it can be 8 too, it will as in the following
testcase happily accept values in the [4, 7] range which shouldn't be
accepted (it can only handle [2, 3]).

Fixed thusly.

2026-02-17  Jakub Jelinek  <jakub@redhat.com>

	PR target/124138
	* config/i386/i386.cc (avx_vpermilp_parallel): Verify
	ipar[2] and ipar[3] aren't larger than 3.

	* gcc.dg/pr124138.c: New test.
	* gcc.target/i386/avx512f-pr124138-1.c: New test.
	* gcc.target/i386/avx512f-pr124138-2.c: New test.

gcc/config/i386/i386.cc

@@ -20701,7 +20701,7 @@ avx_vpermilp_parallel (rtx par, machine_mode mode)
 	}
       for (i = 2; i < 4; ++i)
 	{
-	  if (ipar[i] < 2)
+	  if (ipar[i] < 2 || ipar[i] >= 4)
 	    return 0;
 	  mask |= (ipar[i] - 2) << i;
 	}

gcc/testsuite/gcc.dg/pr124138.c

@@ -0,0 +1,20 @@
+/* PR target/124138 */
+/* { dg-do run } */
+/* { dg-options "-Wno-psabi" } */
+
+typedef __attribute__((__vector_size__ (8 * sizeof (unsigned long long)))) unsigned long long V;
+
+[[gnu::noipa]] V
+foo (V x)
+{
+  return __builtin_shuffle (x, (V) { 0, 1, 2, 5, 4, 5, 6, 7 });
+}
+
+int
+main ()
+{
+  V x = foo ((V) { 1, 2, 3, 4, 5, 6, 7, 8 });
+  if (x[0] != 1 || x[1] != 2 || x[2] != 3 || x[3] != 6
+      || x[4] != 5 || x[5] != 6 || x[6] != 7 || x[7] != 8)
+    __builtin_abort ();
+}

gcc/testsuite/gcc.target/i386/avx512f-pr124138-1.c

@@ -0,0 +1,24 @@
+/* PR target/124138 */
+/* { dg-do run } */
+/* { dg-options "-mavx512f" } */
+/* { dg-require-effective-target avx512f } */
+
+#define AVX512F
+#include "avx512f-helper.h"
+
+typedef __attribute__((__vector_size__ (64))) unsigned long long V;
+
+[[gnu::noipa]] V
+foo (V x)
+{
+  return __builtin_shuffle (x, (V) { 0, 1, 2, 5, 4, 5, 6, 7 });
+}
+
+void
+TEST ()
+{
+  V x = foo ((V) { 1, 2, 3, 4, 5, 6, 7, 8 });
+  if (x[0] != 1 || x[1] != 2 || x[2] != 3 || x[3] != 6
+      || x[4] != 5 || x[5] != 6 || x[6] != 7 || x[7] != 8)
+    __builtin_abort ();
+}

gcc/testsuite/gcc.target/i386/avx512f-pr124138-2.c

@@ -0,0 +1,25 @@
+/* PR target/124138 */
+/* { dg-do run } */
+/* { dg-options "-mavx512f" } */
+/* { dg-require-effective-target avx512f } */
+
+#define AVX512F
+#include "avx512f-helper.h"
+
+typedef __attribute__((__vector_size__ (64))) unsigned long long V;
+typedef __attribute__((__vector_size__ (64))) double W;
+
+[[gnu::noipa]] W
+foo (W x)
+{
+  return __builtin_shuffle (x, (V) { 0, 1, 2, 5, 4, 5, 6, 7 });
+}
+
+void
+TEST ()
+{
+  W x = foo ((W) { 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, 7.5, 8.5 });
+  if (x[0] != 1.5 || x[1] != 2.5 || x[2] != 3.5 || x[3] != 6.5
+      || x[4] != 5.5 || x[5] != 6.5 || x[6] != 7.5 || x[7] != 8.5)
+    __builtin_abort ();
+}