[PATCH, rs6000] Fix PR78556 - left shift of negative values

[Markus Trippelsdorf]

Running bootstrap-ubsan on ppc64le shows many instances of e.g.:
 config/rs6000/rs6000.c:6217:36: runtime error: left shift of negative value 
-12301

The attached patch fixes the issue and was tested on ppc64le.

OK for trunk?

Thanks.

        PR target/78556
        * config/rs6000/rs6000.h (vspltis_constant): Add casts to avoid
        left shifting of negative values.

diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index 6c28e6a..dfb5dc8 100644
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -6214,7 +6214,9 @@ vspltis_constant (rtx op, unsigned step, unsigned copies)
       bitsize /= 2;
       small_val = splat_val >> bitsize;
       mask >>= bitsize;
-      if (splat_val != ((small_val << bitsize) | (small_val & mask)))
+      if (splat_val != ((HOST_WIDE_INT)
+          ((unsigned HOST_WIDE_INT) small_val << bitsize)
+          | (small_val & mask)))
        return false;
       splat_val = small_val;
     }

--
Markus