Thanks for the review.
Eric Botcazou <[email protected]> writes:
>> Tested on x86_64-linux-gnu, mipsisa32-elf and mipsisa64-elf. Also tested
>> by making sure that there were no code differences for a set of gcc .ii
>> files on gcc20 (-O2 -march=native). OK to install?
>
> Are you sure that generating TRUNCATEs out of nowhere in simplify_subreg is
> always correct?
We only use TRUNCATEs when truncating the operands of an existing operation.
We don't convert the SUBREG itself to a TRUNCATE. I don't think it matters
whether the narrowing of the operation was brought about by a TRUNCATE
or by a SUBREG.
I think modelling it as a TRUNCATE operation is correct for
!TRULY_NOOP_TRUNCATION (it's the bug that Andrew pointed out).
And we shouldn't generate an actual TRUNCATE rtx for
TRULY_NOOP_TRUNCATION (the thing about making
simplify_gen_unary (TRUNCATE, ...) no worse than simplify_gen_subreg
for those targets). I suppose:
/* We can't handle truncation to a partial integer mode here
because we don't know the real bitsize of the partial
integer mode. */
if (GET_MODE_CLASS (mode) == MODE_PARTIAL_INT)
break;
might be a problem though; we should still allow a subreg to be
generated. Is that what you were thinking of, or something else?
I'm certainly open to other ideas though. Or do you think that I was
wrong about doing this narrowing in simplify_subreg to begin with?
>> gcc/
>> * machmode.h (GET_MODE_UNIT_PRECISION): New macro.
>> * simplify-rtx.c (simplify_truncation): New function.
>
> You should say where it comes from.
OK.
>> (simplify_unary_operation_1): Use it. Remove sign bit test
>> for !TRULY_NOOP_TRUNCATION_MODES_P.
>
> (simplify_unary_operation_1) <TRUNCATE>: ...
>
>> (simplify_subreg): Use simplify_int_lowpart for TRUNCATE.
>
> This function doesn't exist. And this is misleading, it's not just for
> TRUNCATE, it's for a truncation to the lowpart.
Curses, forgot to update that part. Thanks.
>> /* Try to simplify a unary operation CODE whose output mode is to be
>> MODE with input operand OP whose mode was originally OP_MODE.
>> Return zero if no simplification can be made. */
>> @@ -689,12 +850,6 @@ simplify_unary_operation_1 (enum rtx_cod
>> op_mode = mode;
>> in2 = simplify_gen_unary (NOT, op_mode, in2, op_mode);
>>
>> - if (GET_CODE (in2) == NOT && GET_CODE (in1) != NOT)
>> - {
>> - rtx tem = in2;
>> - in2 = in1; in1 = tem;
>> - }
>> -
>> return gen_rtx_fmt_ee (GET_CODE (op) == IOR ? AND : IOR,
>> mode, in1, in2);
>> }
>
> Why is this hunk here?
Sorry, I've no idea :-(
>> @@ -5595,14 +5730,6 @@ simplify_subreg (enum machine_mode outer
>> return NULL_RTX;
>> }
>>
>> - /* Merge implicit and explicit truncations. */
>> -
>> - if (GET_CODE (op) == TRUNCATE
>> - && GET_MODE_SIZE (outermode) < GET_MODE_SIZE (innermode)
>> - && subreg_lowpart_offset (outermode, innermode) == byte)
>> - return simplify_gen_unary (TRUNCATE, outermode, XEXP (op, 0),
>> - GET_MODE (XEXP (op, 0)));
>> -
>> /* SUBREG of a hard register => just change the register number
>> and/or mode. If the hard register is not valid in that mode,
>> suppress this simplification. If the hard register is the stack,
>
> Likewise.
This moved to simplify_truncation:
/* (truncate:A (truncate:B X)) is (truncate:A X). */
if (GET_CODE (op) == TRUNCATE)
return simplify_gen_unary (TRUNCATE, mode, XEXP (op, 0),
GET_MODE (XEXP (op, 0)));
I haven't included an updated patch because of your general concern above.
Richard
