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Re: Fix PR rtl-optimization/33822
- From: Eric Botcazou <ebotcazou at libertysurf dot fr>
- To: Richard Sandiford <rsandifo at nildram dot co dot uk>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Tue, 18 Dec 2007 18:57:47 +0100
- Subject: Re: Fix PR rtl-optimization/33822
- References: <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org>
> I think rtl.texi already describes the SUBREG_BYTE calculation in enough
> detail, but I noticed that rtl.def was years out of date. I think that
> shows we should have detailed documentation in one place only (rtl.texi),
> so I simplified the rtl.def version.
Interesting left-overs of an old era. :-)
> I've made the comments for update_reg_offset, gen_rtx_REG_offset
> and gen_reg_rtx_offset say "with OFFSET added to the REG_OFFSET"
> rather than "offsetted by OFFSET". I think this, in combination
> with the reg_attrs comment, makes the type of offset more explicit.
> * rtl.def (SUBREG): Update comments.
> * rtl.h (reg_attrs): Be explicit about the type of offset used.
> (set_reg_attrs_from_mem): Rename to...
> (set_reg_attrs_from_value): ...this.
> (adjust_reg_mode, byte_lowpart_offset): Declare.
> * emit-rtl.c (byte_lowpart_offset): New function.
> (update_reg_offset): Remove special offset handling for big-endian
> (gen_rtx_REG_offset, gen_reg_rtx_offset): Explicitly say that the
> offset parameter is added to REG_OFFSET.
> (adjust_reg_mode): New function.
> (set_reg_attrs_for_mem): Rename to...
> (set_reg_attrs_for_value): ...this and generalize to all values.
> If the register is a lowpart of the value, adjust the offset
> (set_reg_attrs_for_parm): Update after the above renaming.
> (set_reg_attrs_for_decl_rtl): New function, split out from
> set_decl_incoming_rtl. Set the offset of plain REGs to the
> offset of the REG's mode from the decl's. Assert that all
> subregs are lowparts and handle their inner registers in the
> same way as plain REGs.
> (set_decl_rtl, set_incoming_decl_rtl): Use reg_attrs_for_decl_rtl.
> (subreg_lowpart_offset): Explicitly say that the returned offset
> is a SUBREG_BYTE.
> * combine.c (do_SUBST_MODE, try_combine, undo_all): Use adjust_reg_mode
> instead of PUT_MODE.
> * final.c (alter_subreg): Fix/update argument to gen_rtx_REG_offset.
> * config/ia64/ia64.c (ia64_expand_load_address): Likewise.
> * regclass.c (reg_scan_mark_refs): Use set_reg_attrs_from_value.
> * reload.c (find_reloads_subreg_address): Call set_mem_offset
> when offseting a MEM.
> * var-tracking.c (offset_valid_for_tracked_p): Delete.
> (mode_for_reg_attrs): Replace with...
> (track_loc_p): ...this new function. Return the mode and offset
> to the caller, checking that the latter is valid. If the rtx is
> a paradoxical lowpart of the decl, use the decl's mode instead.
> Do the same when storing to a register that contains the entire decl.
> (var_lowpart): Use byte_lowpart_offset rather than
> subreg_lowpart_offset when adjusting the offset attribute.
> (count_uses, add_uses, add_stores): Use track_reg_p instead of
> REG_EXPR, MEM_EXPR, REG_OFFSET, INT_MEM_OFFSET, track_expr_p,
> offset_valid_for_tracked_p and mode_for_reg_attrs. Generate
> lowparts for MEMs as well as REGs.
> (vt_add_function_parameters): When obtaining the information from
> the decl_rtl, adjust the offset to match incoming. Use track_loc_p
> and var_lowpart.
Btw, could we do something clever for the many similar calculations in
alter_subreg and simplify_subreg (and maybe elsewhere):
/* The SUBREG_BYTE represents offset, as if the value were stored
in memory. Irritating exception is paradoxical subreg, where
we define SUBREG_BYTE to be 0. On big endian machines, this
value should be negative. For a moment, undo this exception. */
if (byte == 0 && GET_MODE_SIZE (innermode) < GET_MODE_SIZE (outermode))
int difference = (GET_MODE_SIZE (innermode) - GET_MODE_SIZE (outermode));
final_offset += (difference / UNITS_PER_WORD) * UNITS_PER_WORD;
final_offset += difference % UNITS_PER_WORD;