https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54089
--- Comment #89 from Alexander Klepikov <klepikov.alex+bugs at gmail dot com>
---
Here's what I did
sh.md:
(define_expand "ashrsi3"
[(parallel [(set (match_operand:SI 0 "arith_reg_dest" "")
(ashiftrt:SI (match_operand:SI 1 "arith_reg_operand" "")
(match_operand:SI 2 "nonmemory_operand" "")))
(clobber (reg:SI T_REG))])]
""
{
if (expand_ashiftrt (operands))
DONE;
if (!CONST_INT_P (operands[2]))
FAIL;
int value = INTVAL (operands[2]) & 31;
emit_insn (gen_ashrsi3_n_call (operands[0], operands[1], GEN_INT(value)));
DONE;
})
(define_insn_and_split "ashrsi3_n_call"
[(set (match_operand:SI 0 "arith_reg_dest" "=r")
(ashiftrt:SI (match_operand:SI 1 "arith_reg_operand" "0")
(match_operand:SI 2 "const_int_operand")))
(clobber (reg:SI T_REG))]
"TARGET_SH1"
"#"
"&& can_create_pseudo_p ()"
[(const_int 0)]
{
char func[18];
int value;
rtx wrk;
cfun->machine->ashrsi3_libcall_expanded++;
if (expand_ashiftrt (operands))
DONE;
if (!CONST_INT_P (operands[2]))
FAIL;
value = INTVAL (operands[2]) & 31;
if (dump_file)
fprintf(dump_file, "ashrsi3_n_call: Expanding ashrsi3 libcall\n");
wrk = gen_reg_rtx (Pmode);
/* Load the value into an arg reg and call a helper. */
emit_move_insn (gen_rtx_REG (SImode, 4), operands[1]);
sprintf (func, "__ashiftrt_r4_%d", value);
rtx lab = function_symbol (wrk, func, SFUNC_STATIC).lab;
emit_insn (gen_ashrsi3_n (GEN_INT (value), wrk, lab));
emit_move_insn (operands[0], gen_rtx_REG (SImode, 4));
DONE;
})
sh.cc:
bool
expand_ashiftrt (rtx *operands)
{
rtx wrk;
int value;
if (TARGET_DYNSHIFT)
{
if (!CONST_INT_P (operands[2]))
{
rtx count = copy_to_mode_reg (SImode, operands[2]);
emit_insn (gen_negsi2 (count, count));
emit_insn (gen_ashrsi3_d (operands[0], operands[1], count));
return true;
}
else if (ashiftrt_insns[INTVAL (operands[2]) & 31]
> 1 + SH_DYNAMIC_SHIFT_COST)
{
rtx count
= force_reg (SImode, GEN_INT (- (INTVAL (operands[2]) & 31)));
emit_insn (gen_ashrsi3_d (operands[0], operands[1], count));
return true;
}
}
if (!CONST_INT_P (operands[2]))
return false;
value = INTVAL (operands[2]) & 31;
if (value == 31)
{
/* If we are called from abs expansion, arrange things so that we
we can use a single MT instruction that doesn't clobber the source,
if LICM can hoist out the load of the constant zero. */
if (currently_expanding_to_rtl)
{
emit_insn (gen_cmpgtsi_t (force_reg (SImode, CONST0_RTX (SImode)),
operands[1]));
emit_insn (gen_mov_neg_si_t (operands[0], get_t_reg_rtx ()));
return true;
}
emit_insn (gen_ashrsi2_31 (operands[0], operands[1]));
return true;
}
else if (value >= 16 && value <= 19)
{
wrk = gen_reg_rtx (SImode);
emit_insn (gen_ashrsi2_16 (wrk, operands[1]));
value -= 16;
while (value--)
gen_ashift (ASHIFTRT, 1, wrk);
emit_move_insn (operands[0], wrk);
return true;
}
/* Expand a short sequence inline, longer call a magic routine. */
else if (value <= 5)
{
wrk = gen_reg_rtx (SImode);
emit_move_insn (wrk, operands[1]);
while (value--)
gen_ashift (ASHIFTRT, 1, wrk);
emit_move_insn (operands[0], wrk);
return true;
}
return false;
}
Now GCC falls into infinite loop when compiling this:
int f_short_rshift_signed(char v){
return v >> 5;
}
It looks like it splits and then combines again.
