[Patch,AVR]: Fix PR39386 (x << x and x >> x)

[Georg-Johann Lay]

This is a fix for pathological, variable shift offset shifts of
the form x << x resp. x >> x.

Such shifts need a shift register which might overlap with the
shift operand.

unsigned char shift (unsigned int x)
{
    return x << x;
}


Without patch, note r24 is part of operand and used in loop:

shift:
        rjmp 2f
1:      lsl r24
        rol r25
2:      dec r24
        brpl 1b
        ret

With patch use tmp_reg (R0) as counter:

shift:
        mov r0,r24
        rjmp 2f
1:      lsl r24
        rol r25
2:      dec r0
        brpl 1b
        ret

Patch as obvious. Increased instruction length is already
taken into account because the RO = Rx will be needed if
Rx is used afterwards, anyway.

Ok to install?

Johann


        PR target/39386
        * config/avr/avr.c (out_shift_with_cnt): Use tmp_reg as
        shift counter for x << x and x >> x shifts.


Index: config/avr/avr.c
===================================================================
--- config/avr/avr.c	(revision 176624)
+++ config/avr/avr.c	(working copy)
@@ -3147,8 +3147,11 @@ out_shift_with_cnt (const char *templ, r
     }
   else if (register_operand (operands[2], QImode))
     {
-      if (reg_unused_after (insn, operands[2]))
-	op[3] = op[2];
+      if (reg_unused_after (insn, operands[2])
+          && !reg_overlap_mentioned_p (operands[0], operands[2]))
+        {
+          op[3] = op[2];
+        }
       else
 	{
 	  op[3] = tmp_reg_rtx;