"Robin Dapp" <[email protected]> writes:
> Grml, setting REGMODE_NATURAL_SIZE for advsimd modes as well uncovered
> several
> other lower-subreg issues and it, again, turned into a game of whack-a-mole
> and
> obviously took way longer than I would have hoped.
Yeah, the aarch64 change looks good to me (but I shouldn't approve it).
And sorry for the late reply. Since like you said the lower-subreg
changes came from whack-a-mole, I kind-of needed to play the same game
to review.
An aarch64 bootstrap & regression test succeeded for me except for:
FAIL: gcc.target/aarch64/simd/fold_to_highpart_6.c check-function-bodies
test_256b_type
with:
1. the read_complex_part change (already approved)
2. the expemd.cc changes (already approved)
3. the interesting_mode_p change
4. the change below
5. the aarch64 change
Do (3) and (4) work for you too, or do you still need some of the other
lower-subreg changes from your patch? Could you give an example if so?
> @@ -4714,6 +4711,22 @@ emit_move_insn (rtx x, rtx y)
> mode = GET_MODE (x_inner);
> }
>
> + /* If we don't have a move for MODE, emit_move_insn_1 will fall back to
> + emit_move_multi_word at which point we'll try to decompose the
> + inner reg via operand_subword_force. If that fails we're back
> + here again without having made progress.
> + Therefore, spill Y to memory before we cannot escape anymore. */
> + rtx yreg = SUBREG_P (y) ? SUBREG_REG (y) : y;
> + if (optab_handler (mov_optab, mode) == CODE_FOR_nothing
> + && maybe_lt ((unsigned) UNITS_PER_WORD,
> + (poly_uint64) REGMODE_NATURAL_SIZE (GET_MODE (yreg))))
> + {
> + rtx mem = assign_stack_temp (GET_MODE (yreg),
> + GET_MODE_SIZE (GET_MODE (yreg)));
> + emit_move_insn (mem, yreg);
> + y = adjust_address (mem, mode, 0);
The 0 would need to be subreg_memory_offset (y) when y is a subreg.
But this might still go wrong for paradoxical subregs, where we could
read beyond the stack temporary.
Could you list some of the testcases that fail for RISC-V without the
emit_move_insn change? (Maybe you already did, sorry.)
I won't be able to reply for a week or so. I'll have a look at
fold_to_highpart_6.c when I get back.
Thanks,
Richard
diff --git a/gcc/lower-subreg.cc b/gcc/lower-subreg.cc
index 5dee6a0b646..3d0654e7d93 100644
--- a/gcc/lower-subreg.cc
+++ b/gcc/lower-subreg.cc
@@ -302,7 +304,21 @@ static bool
simple_move_operand (rtx x)
{
if (GET_CODE (x) == SUBREG)
- x = SUBREG_REG (x);
+ {
+ /* Exclude subregs whose outer mode can be split into multiple words
+ but whose inner mode cannot. Attempting to split such a subreg
+ would mean trying to split the unsplittable inner register.
+
+ If instead the subreg occupies a single word, we can keep it as-is,
+ regardless of what the SUBREG_REG is. If the outer mode cannot be
+ split then the subreg makes things no worse than they already are. */
+ unsigned int factor, size;
+ if (interesting_mode_p (GET_MODE (x), &size, &factor)
+ && factor > 1
+ && !interesting_mode_p (GET_MODE (SUBREG_REG (x)), &size, &factor))
+ return false;
+ x = SUBREG_REG (x);
+ }
if (!OBJECT_P (x))
return false;
