On Sun, Oct 7, 2012 at 8:56 AM, Richard Sandiford <rdsandif...@googlemail.com> wrote: > Eric Botcazou <ebotca...@adacore.com> writes: >>> 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 was thinking of the !TRULY_NOOP_TRUNCATION case, where the two operations >> aren't equivalent. Generating TRUNCATE in simplify_subreg seems suspicious >> to >> me in this case but, if not doing it is the source of the bug, I guess I need >> to do some homework on this TRULY_NOOP_TRUNCATION stuff. :-) >> >> Maybe add a blurb to the head comment of simplify_truncation, explaining that >> it is valid to call the function both for TRUNCATEs and truncations to the >> lowpart, and why it is correct to generate new TRUNCATEs in the latter case. > > Yeah, in hindsight, the patch was definitely lacking commentary. > How about the patch below? It also fixes the partial int case > and gets rid of the errant NOT hunk. Tested in the same way as before. > > Richard > > > gcc/ > * machmode.h (GET_MODE_UNIT_PRECISION): New macro. > * simplify-rtx.c (simplify_truncation): New function, > extracted from simplify_subreg and (in small part) from > simplify_unary_operation_1. > (simplify_unary_operation_1) <TRUNCATE>: Use it. Remove sign bit > test for !TRULY_NOOP_TRUNCATION_MODES_P. > (simplify_subreg): Use simplify_truncate for lowpart subregs > where both the inner and outer modes are scalar integers. > * config/mips/mips.c (mips_truncated_op_cost): New function. > (mips_rtx_costs): Adjust test for BADDU. > * config/mips/mips.md (*baddu_di<mode>): Push truncates to operands.
This triggers PR55052 on ARM.I've attached the .i file and the dumps to the bug report. Thanks, Ramana
