[Bug target/94710] [8/9/10 Regression] Assembler messages: Error: operand out of range (4 is not between 0 and 3) (xxsldwi 0,32,33,4)

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94710

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
For the middle-end side, I think we can do:
2020-04-23  Jakub Jelinek  <ja...@redhat.com>

        PR target/94710
        * optabs.c (expand_vec_perm_const): For shift_amt const0_rtx
        just return v2.

--- gcc/optabs.c.jj     2020-04-17 14:18:44.380437703 +0200
+++ gcc/optabs.c        2020-04-23 11:50:07.931780323 +0200
@@ -5627,6 +5627,8 @@ expand_vec_perm_const (machine_mode mode
       if (shift_amt)
        {
          class expand_operand ops[3];
+         if (shift_amt == const0_rtx)
+           return v2;
          if (shift_code != CODE_FOR_nothing)
            {
              create_output_operand (&ops[0], target, mode);

Though, the backend shouldn't rely on the middle-end doing this optimization.