ARC: Split asl dst,1,src into bset dst,0,src to implement 1<<x.

This patch adds a pre-reload splitter to arc.md, to use the bset (set
specific bit instruction) to implement 1<<x (i.e. left shifts of one)
on ARC processors that don't have a barrel shifter.

Currently,

int foo(int x) {
  return 1 << x;
}

when compiled with -O2 -mcpu=em is compiled as a loop:

foo:	mov_s   r2,1    ;3
        and.f lp_count,r0, 0x1f
        lpnz    2f
        add r2,r2,r2
        nop
2:      # end single insn loop
        j_s.d   [blink]
        mov_s   r0,r2   ;4

with this patch we instead generate a single instruction:

foo:	bset    r0,0,r0
        j_s     [blink]

2023-10-16  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* config/arc/arc.md (*ashlsi3_1): New pre-reload splitter to
	use bset dst,0,src to implement 1<<x on !TARGET_BARREL_SHIFTER.

0 files changed, 0 insertions, 0 deletions