[PATCH] Fix simplify-rtx.c handling of avx512 vector comparisons (PR target/92908)

[Richard Biener]

On December 12, 2019 12:56:01 AM GMT+01:00, Jakub Jelinek <jakub@redhat.com> wrote:
>Hi!
>
>The AVX512{F,VL} vector comparisons that set %kN registers are
>represented
>in RTL as comparisons with vector mode operands and scalar integral
>result,
>where at runtime the scalar integer is filled with a bitmask.
>Unfortunately, simplify_relational_operation would fold e.g.
>(eq:SI (reg:V32HI x) (reg:V32HI x))
>into (const_int 1) rather than (const_int -1) that is expected (all
>elements
>equal).  simplify_const_relational_operation is documented to always
>return
>just const0_rtx or const_true_rtx and simplify_relational_operation is
>expected to fix this up, for vector comparisons with vector result it
>duplicates the 0 or -1 into all elements, etc., so this patch adds
>handling
>for this case there too.
>
>Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

So there's no whole vector equality RTX but we have to pun to integer modes for that? The eq:SImode would suggest that. Guess we should have used a BImode vector representation... 

Can you check whether we have any target with whole vector compare patterns that would break here? 

Richard. 

>2019-12-11  Jakub Jelinek  <jakub@redhat.com>
>
>	PR target/92908
>	* simplify-rtx.c (simplify_relational_operation): For vector cmp_mode
>	and scalar mode, if simplify_relational_operation returned
>	const_true_rtx, return a scalar bitmask of all ones.
>	(simplify_const_relational_operation): Change VOID_mode in function
>	comment to VOIDmode.
>
>	* gcc.target/i386/avx512bw-pr92908.c: New test.
>
>--- gcc/simplify-rtx.c.jj	2019-11-19 22:27:02.000058742 +0100
>+++ gcc/simplify-rtx.c	2019-12-11 13:31:57.197809704 +0100
>@@ -5037,6 +5037,23 @@ simplify_relational_operation (enum rtx_
> 	  return NULL_RTX;
> #endif
> 	}
>+      if (VECTOR_MODE_P (cmp_mode)
>+	  && SCALAR_INT_MODE_P (mode)
>+	  && tem == const_true_rtx)
>+	{
>+	  /* Vector comparisons that expect a scalar integral
>+	     bitmask.  For const0_rtx the result is already correct,
>+	     for const_true_rtx we need all bits set.  */
>+	  int n_elts;
>+	  scalar_int_mode smode = as_a <scalar_int_mode> (mode);
>+	  gcc_assert (GET_MODE_NUNITS (cmp_mode).is_constant (&n_elts)
>+		      && GET_MODE_PRECISION (smode) <= n_elts);
>+	  if (GET_MODE_PRECISION (smode) == n_elts)
>+	    return constm1_rtx;
>+	  if (n_elts < HOST_BITS_PER_WIDE_INT)
>+	    return GEN_INT ((HOST_WIDE_INT_1U << n_elts) - 1);
>+	  return NULL_RTX;
>+	}
> 
>       return tem;
>     }
>@@ -5383,7 +5400,7 @@ comparison_result (enum rtx_code code, i
> }
> 
> /* Check if the given comparison (done in the given MODE) is actually
>-   a tautology or a contradiction.  If the mode is VOID_mode, the
>+   a tautology or a contradiction.  If the mode is VOIDmode, the
>    comparison is done in "infinite precision".  If no simplification
>    is possible, this function returns zero.  Otherwise, it returns
>    either const_true_rtx or const0_rtx.  */
>--- gcc/testsuite/gcc.target/i386/avx512bw-pr92908.c.jj	2019-12-11
>14:24:12.083418762 +0100
>+++ gcc/testsuite/gcc.target/i386/avx512bw-pr92908.c	2019-12-11
>14:23:56.071665326 +0100
>@@ -0,0 +1,21 @@
>+/* PR target/92908 */
>+/* { dg-do run } */
>+/* { dg-options "-Og -fno-tree-fre -mavx512bw" } */
>+/* { dg-require-effective-target avx512bw } */
>+
>+#define AVX512BW
>+#include "avx512f-helper.h"
>+
>+typedef unsigned short V __attribute__ ((__vector_size__ (64)));
>+
>+V v;
>+
>+void
>+TEST (void)
>+{
>+  int i;
>+  v = (V) v == v;
>+  for (i = 0; i < 32; i++)
>+    if (v[i] != 0xffff)
>+      abort ();
>+}
>
>	Jakub