[gcc r10-8323] forwprop: simplify_vector_constructor follow-up fix [PR95713]

[gcc r10-8323] forwprop: simplify_vector_constructor follow-up fix [PR95713]

[Jakub Jelinek]

https://gcc.gnu.org/g:0c7d18d51a8e9abd085afd0b01743662fd0419fa

commit r10-8323-g0c7d18d51a8e9abd085afd0b01743662fd0419fa
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Jun 18 12:08:06 2020 +0200

    forwprop: simplify_vector_constructor follow-up fix [PR95713]
    
    As the following testcase shows, the exception for the aarch64
    vec_pack_trunc_di is not sufficient on x86, the halfvectype
    "vectors" have SImode but the x86 vec_pack_trunc_si meant for
    the bool bitmasks combines 2x SImode into DImode, while in the
    testcase the halfvectype is 1x SImode "vector" with SImode and
    result is 2x HImode "vector" with SImode.
    
    Richard Sandiford's reply:
    FWIW, since the aarch64 case was only found by inspection and might
    not be useful, personally I'd prefer to drop that case after all.
    
    2020-06-18  Jakub Jelinek  <jakub@redhat.com>
    
            PR target/95713
            * tree-ssa-forwprop.c (simplify_vector_constructor): Don't allow
            scalar mode halfvectype other than vector boolean for
            VEC_PACK_TRUNC_EXPR.
    
            * gcc.dg/pr95713.c: New test.
    
    (cherry picked from commit 9a875db43cd4210843c480c8df26a1d6624d057d)

Diff:
---
 gcc/testsuite/gcc.dg/pr95713.c | 15 +++++++++++++++
 gcc/tree-ssa-forwprop.c        | 11 ++++-------
 2 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/pr95713.c b/gcc/testsuite/gcc.dg/pr95713.c
new file mode 100644
index 00000000000..b167842b963
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr95713.c
@@ -0,0 +1,15 @@
+/* PR target/95713 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wno-psabi -w" } */
+/* { dg-additional-options "-mavx512bw" { target i?86-*-* x86_64-*-* } } */
+
+typedef int v2si __attribute__((vector_size (8)));
+typedef short int v2hi __attribute__((vector_size (4)));
+void foo (v2hi);
+
+void
+bar (v2si x)
+{
+  v2hi a = (v2hi) { (short) x[0], (short) x[1] };
+  foo (4 > a);
+}
diff --git a/gcc/tree-ssa-forwprop.c b/gcc/tree-ssa-forwprop.c
index 0ab0f95d507..399422f92d1 100644
--- a/gcc/tree-ssa-forwprop.c
+++ b/gcc/tree-ssa-forwprop.c
@@ -2401,8 +2401,8 @@ simplify_vector_constructor (gimple_stmt_iterator *gsi)
 	      && (dblvectype
 		  = build_vector_type (TREE_TYPE (TREE_TYPE (orig[0])),
 				       nelts * 2))
-	      /* Only use it for vector modes or for vector booleans represented
-		 as scalar bitmasks.  See PR95528.  */
+	      /* Only use it for vector modes or for vector booleans
+		 represented as scalar bitmasks.  See PR95528.  */
 	      && (VECTOR_MODE_P (TYPE_MODE (dblvectype))
 		  || VECTOR_BOOLEAN_TYPE_P (dblvectype))
 	      && (optab = optab_for_tree_code (FLOAT_TYPE_P (TREE_TYPE (type))
@@ -2447,12 +2447,9 @@ simplify_vector_constructor (gimple_stmt_iterator *gsi)
 		         = build_vector_type (TREE_TYPE (TREE_TYPE (orig[0])),
 					      nelts / 2))
 		   /* Only use it for vector modes or for vector booleans
-		      represented as scalar bitmasks, or allow halfvectype
-		      be the element mode.  See PR95528.  */
+		      represented as scalar bitmasks.  See PR95528.  */
 		   && (VECTOR_MODE_P (TYPE_MODE (halfvectype))
-		       || VECTOR_BOOLEAN_TYPE_P (halfvectype)
-		       || (TYPE_MODE (halfvectype)
-			   == TYPE_MODE (TREE_TYPE (halfvectype))))
+		       || VECTOR_BOOLEAN_TYPE_P (halfvectype))
 		   && (optab = optab_for_tree_code (VEC_PACK_TRUNC_EXPR,
 						    halfvectype,
 						    optab_default))