[gcc r9-10092] rs6000: Fix up easy_vector_constant_msb handling [PR101384]

[gcc r9-10092] rs6000: Fix up easy_vector_constant_msb handling [PR101384]

[Jakub Jelinek]

https://gcc.gnu.org/g:883690ff6bd8e4f16c871b307cebb13d6c14edcb

commit r9-10092-g883690ff6bd8e4f16c871b307cebb13d6c14edcb
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Jul 20 16:41:29 2021 +0200

    rs6000: Fix up easy_vector_constant_msb handling [PR101384]
    
    The following gcc.dg/pr101384.c testcase is miscompiled on
    powerpc64le-linux.
    easy_altivec_constant has code to try construct vector constants with
    different element sizes, perhaps different from CONST_VECTOR's mode.  But as
    written, that works fine for vspltis[bhw] cases, but not for the vspltisw
    x,-1; vsl[bhw] x,x,x case, because that creates always a V16QImode, V8HImode
    or V4SImode constant containing broadcasted constant with just the MSB set.
    The vspltis_constant function etc. expects the vspltis[bhw] instructions
    where the small [-16..15] or even [-32..30] constant is sign-extended to the
    remaining step bytes, but that is not the case for the 0x80...00 constants,
    with step 1 we can't handle e.g.
    { 0x80, 0xff, 0xff, 0xff, 0x80, 0xff, 0xff, 0xff, 0x80, 0xff, 0xff, 0xff, 0x80, 0xff, 0xff, 0xff }
    vectors but do want to handle e.g.
    { 0, 0, 0, 0x80, 0, 0, 0, 0x80, 0, 0, 0, 0x80, 0, 0, 0, 0x80 }
    and similarly with copies 1 we do want to handle e.g.
    { 0x80808080, 0x80808080, 0x80808080, 0x80808080 }.
    
    This is a simpler version of the fix for backports, which limits the EASY_VECTOR_MSB case
    matching to step == 1 && copies == 1, because that is the only case the
    splitter handles correctly.
    
    2021-07-20  Jakub Jelinek  <jakub@redhat.com>
    
            PR target/101384
            * config/rs6000/rs6000.c (vspltis_constant): Accept EASY_VECTOR_MSB
            only if step and copies are equal to 1.
    
            * gcc.dg/pr101384.c: New test.
    
    (cherry picked from commit dc386b020869ad0095cf58f8c76a40ea457e7a2c)

Diff:
---
 gcc/config/rs6000/rs6000.c      |  2 +-
 gcc/testsuite/gcc.dg/pr101384.c | 39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index a6e683fe2df..84d93f79343 100644
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -6081,7 +6081,7 @@ vspltis_constant (rtx op, unsigned step, unsigned copies)
 
   /* Also check if are loading up the most significant bit which can be done by
      loading up -1 and shifting the value left by -1.  */
-  else if (EASY_VECTOR_MSB (splat_val, inner))
+  else if (EASY_VECTOR_MSB (splat_val, inner) && step == 1 && copies == 1)
     ;
 
   else
diff --git a/gcc/testsuite/gcc.dg/pr101384.c b/gcc/testsuite/gcc.dg/pr101384.c
new file mode 100644
index 00000000000..7030c0a481e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr101384.c
@@ -0,0 +1,39 @@
+/* PR target/101384 */
+/* { dg-do run } */
+/* { dg-options "-O2 -Wno-psabi -w" } */
+
+typedef unsigned char __attribute__((__vector_size__ (16))) U;
+typedef unsigned short __attribute__((__vector_size__ (8 * sizeof (short)))) V;
+
+U u;
+V v;
+
+__attribute__((noipa)) U
+foo (void)
+{
+  U y = (U) { 0x80, 0xff, 0xff, 0xff, 0x80, 0xff, 0xff, 0xff,
+              0x80, 0xff, 0xff, 0xff, 0x80, 0xff, 0xff, 0xff } + u;
+  return y;
+}
+
+__attribute__((noipa)) V
+bar (void)
+{
+  V y = (V) { 0x8000, 0xffff, 0x8000, 0xffff,
+              0x8000, 0xffff, 0x8000, 0xffff } + v;
+  return y;
+}
+
+int
+main ()
+{
+  U x = foo ();
+  for (unsigned i = 0; i < 16; i++)
+    if (x[i] != ((i & 3) ? 0xff : 0x80))
+      __builtin_abort ();
+  V y = bar ();
+  for (unsigned i = 0; i < 8; i++)
+    if (y[i] != ((i & 1) ? 0xffff : 0x8000))
+      __builtin_abort ();
+  return 0;
+}