[PATCH] Fix native_encode_vector_part for itype when TYPE_PRECISION (itype) == BITS_PER_UNIT

[liuhongt]

for the testcase in the PR115406, here is part of the dump.

  char D.4882;
  vector(1) <signed-boolean:8> _1;
  vector(1) signed char _2;
  char _5;

  <bb 2> :
  _1 = { -1 };

When assign { -1 } to vector(1} {signed-boolean:8},
Since TYPE_PRECISION (itype) <= BITS_PER_UNIT, so it set each bit of dest
with each vector elemnet. But i think the bit setting should only apply for
TYPE_PRECISION (itype) < BITS_PER_UNIT. .i.e for vector(1).
<signed-boolean:16>, it will be assigned as -1, instead of 1.
Is there any specific reason vector(1) <signed-boolean:8> is handled
differently from vector<1> <signed-boolean:16>?

Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}.
Ok for trunk?

gcc/ChangeLog:

        PR middle-end/115406
        * fold-const.cc (native_encode_vector_part): Don't set each
        bit to the dest when TYPE_PRECISION (itype) == BITS_PER_UNIT.

gcc/testsuite/ChangeLog:

        * gcc.target/i386/pr115406.c: New test.
---
 gcc/fold-const.cc                        |  2 +-
 gcc/testsuite/gcc.target/i386/pr115406.c | 23 +++++++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.target/i386/pr115406.c

diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index 710d697c021..0f045f851d1 100644
--- a/gcc/fold-const.cc
+++ b/gcc/fold-const.cc
@@ -8077,7 +8077,7 @@ native_encode_vector_part (const_tree expr, unsigned char 
*ptr, int len,
 {
   tree itype = TREE_TYPE (TREE_TYPE (expr));
   if (VECTOR_BOOLEAN_TYPE_P (TREE_TYPE (expr))
-      && TYPE_PRECISION (itype) <= BITS_PER_UNIT)
+      && TYPE_PRECISION (itype) < BITS_PER_UNIT)
     {
       /* This is the only case in which elements can be smaller than a byte.
         Element 0 is always in the lsb of the containing byte.  */
diff --git a/gcc/testsuite/gcc.target/i386/pr115406.c 
b/gcc/testsuite/gcc.target/i386/pr115406.c
new file mode 100644
index 00000000000..623dff06fc3
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr115406.c
@@ -0,0 +1,23 @@
+/* { dg-do run } */
+/* { dg-options "-O0 -mavx512f" } */
+/* { dg-require-effective-target avx512f } */
+
+typedef __attribute__((__vector_size__ (1))) char V;
+
+char
+foo (V v)
+{
+  return ((V) v == v)[0];
+}
+
+int
+main ()
+{
+  if (!__builtin_cpu_supports ("avx512f"))
+    return 0;
+
+  char x = foo ((V) { });
+  if (x != -1)
+    __builtin_abort ();
+  return 0;
+}
-- 
2.31.1