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

[Jakub Jelinek]

On Thu, Dec 12, 2019 at 04:59:40PM +0100, Richard Biener wrote:
> >If it starts being ambiguous somewhere, could we use some target macro
> >or
> >target hook to decide? 
> 
> Ambiguous IL is bad :/  IL semantics dependent on a target hook, too. Just look at SHIFT_COUNT_TRUNCATED... 

This is something I've also successfully bootstrapped/regtested on
x86_64-linux and i686-linux:

2019-12-11  Jakub Jelinek  <jakub@redhat.com>

	PR target/92908
	* simplify-rtx.c (simplify_relational_operation): Punt for vector
	cmp_mode and scalar mode, if simplify_relational_operation returned
	const_true_rtx.
	(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 +5037,15 @@ simplify_relational_operation (enum rtx_
 	  return NULL_RTX;
 #endif
 	}
+      /* For vector comparison with scalar int result, it is unknown
+	 if the target means here a comparison into an integral bitmask,
+	 or comparison where all comparisons true mean const_true_rtx
+	 whole result, or where any comparisons true mean const_true_rtx
+	 whole result.  For const0_rtx all the cases are the same.  */
+      if (VECTOR_MODE_P (cmp_mode)
+	  && SCALAR_INT_MODE_P (mode)
+	  && tem == const_true_rtx)
+	return NULL_RTX;
 
       return tem;
     }
@@ -5383,7 +5392,7 @@ 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