On Wed, Feb 12, 2025 at 6:25 AM H.J. Lu <hjl.to...@gmail.com> wrote:
>
> Don't assume that stack slots can only be accessed by stack or frame
> registers. We first find all registers defined by stack or frame
> registers. Then check memory accesses by such registers, including
> stack and frame registers.
>
> gcc/
>
> PR target/109780
> PR target/109093
> * config/i386/i386.cc (ix86_update_stack_alignment): New.
> (ix86_find_all_reg_use): Likewise.
> (ix86_find_max_used_stack_alignment): Also check memory accesses
> from registers defined by stack or frame registers.
>
> gcc/testsuite/
>
> PR target/109780
> PR target/109093
> * g++.target/i386/pr109780-1.C: New test.
> * gcc.target/i386/pr109093-1.c: Likewise.
> * gcc.target/i386/pr109780-1.c: Likewise.
> * gcc.target/i386/pr109780-2.c: Likewise.
> +/* Find all registers defined with REG. */
> +
> +static void
> +ix86_find_all_reg_use (HARD_REG_SET &stack_slot_access,
> + unsigned int reg, auto_bitmap &worklist)
> +{
> + for (df_ref ref = DF_REG_USE_CHAIN (reg);
> + ref != NULL;
> + ref = DF_REF_NEXT_REG (ref))
> + {
> + if (DF_REF_IS_ARTIFICIAL (ref))
> + continue;
> +
> + rtx_insn *insn = DF_REF_INSN (ref);
> + if (!NONDEBUG_INSN_P (insn))
> + continue;
> +
> + rtx set = single_set (insn);
> + if (!set)
> + continue;
> +
Isn't the above condition a bit too limiting? We can have insn with
multiple sets in the chain.
The issue at hand is the correctness issue (the program will segfault
if registers are not tracked correctly), not some missing
optimization. I'd suggest to stay on the safe side and also process
PARALLELs. Something similar to e.g. store_data_bypass_p from
recog.cc:
--cut here--
rtx set = single_set (insn);
if (set)
ix86_find_all_reg_use_1(...);
rtx pat = PATTERN (insn);
if (GET_CODE (pat) != PARALLEL)
return false;
for (int i = 0; i < XVECLEN (pat, 0); i++)
{
rtx exp = XVECEXP (pat, 0, i);
if (GET_CODE (exp) == CLOBBER || GET_CODE (exp) == USE)
continue;
gcc_assert (GET_CODE (exp) == SET);
ix86_find_all_reg_use_1(...);
}
--cut here--
The above will make ix86_find_all_reg_use significantly more robust.
Uros.
