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Ping: [RFA:] Fix frame-pointer-clobbering in builtins.c:expand_builtin_setjmp_receiver
CC:ing middle-end maintainers this time. I was a bit surprised
when Eric Botcazou wrote in his review, quoted below, that he's
not one of you. Maybe approve that too?
On Mon, 15 Oct 2012, Hans-Peter Nilsson wrote:
> On Fri, 12 Oct 2012, Eric Botcazou wrote:
> > > (insn 168 49 51 3 (set (reg/f:DI 253 $253)
> > > (plus:DI (reg/f:DI 253 $253)
> > > (const_int 24 [0x18])))
> > > /tmp/mmiximp2/gcc/gcc/testsuite/gcc.c-torture/execute/built-in-setjmp.c:21
> > > -1 (nil))
> > > (insn 51 168 52 3 (clobber (reg/f:DI 253 $253))
> ...
>
> > > Note that insn 168 deleted, which seems a logical optimization. The
> > > bug is to emit the clobber, not that the restoring insn is removed.
> >
> > Had that worked in the past for MMIX?
>
> Yes, for svn revision 106027 (20051030) 4.1.0-era (!)
> <http://gcc.gnu.org/ml/gcc-testresults/2005-10/msg01340.html>
> where the test must have passed, as
> gcc.c-torture/execute/built-in-setjmp.c is at least four years
> older than that.
>
> > If so, what changed recently?
>
> By "these days" I didn't mean "recent", just not "eons ago". :)
> I see in a gcc-test-results posting from Mike Stein (whom I'd
> like to thank for test-results posting over the years), matching
> FAILs for svn revision 126095 (20070628) 4.3.0-era
> <http://gcc.gnu.org/ml/gcc-testresults/2007-06/msg01287.html>.
>
> Sorry, I have nothing in between those reports, my bad. Though
> I see no point narrowing down the failing revision further here
> IMO; as mentioned the bug is not that the restoring insn is
> removed.
>
> > Agreed. However, I'd suggest rescuing the comment for the ELIMINABLE_REGS
> > block from expand_nl_goto_receiver as it still sounds valid to me.
>
> Oops, my bad; I see I removed all the good comments. Fixed.
>
> > > * stmt.c (expand_nl_goto_receiver): Remove almost-copy of
> > > expand_builtin_setjmp_receiver.
> > > (expand_label): Adjust, call expand_builtin_setjmp_receiver
> > > with NULL for the label parameter.
> > > * builtins.c (expand_builtin_setjmp_receiver): Don't clobber
> > > the frame-pointer. Adjust comments.
> > > [HAVE_builtin_setjmp_receiver]: Emit builtin_setjmp_receiver
> > > only if LABEL is non-NULL.
> >
> > I cannot formally approve, but this looks good to me modulo:
>
> > > + If RECEIVER_LABEL is NULL, instead the port-specific parts of a
> > > + nonlocal goto handler are emitted. */
> >
> > The "port-specific parts" wording is a bit confusing I think. I'd just write:
> >
> > If RECEIVER_LABEL is NULL, instead contruct a nonlocal goto handler.
>
> Sure. Thanks for the review. Updated patch below. As nothing
> was changed from the previous post but comments as per the
> review (mostly moving / reviving, fixing one grammo), already
> covered by the changelog quoted above, the previous testing is
> still valid.
>
> Ok for trunk, approvers?
>
> Index: gcc/builtins.c
> ===================================================================
> --- gcc/builtins.c (revision 192353)
> +++ gcc/builtins.c (working copy)
> @@ -885,14 +885,15 @@ expand_builtin_setjmp_setup (rtx buf_add
> }
>
> /* Construct the trailing part of a __builtin_setjmp call. This is
> - also called directly by the SJLJ exception handling code. */
> + also called directly by the SJLJ exception handling code.
> + If RECEIVER_LABEL is NULL, instead contruct a nonlocal goto handler. */
>
> void
> expand_builtin_setjmp_receiver (rtx receiver_label ATTRIBUTE_UNUSED)
> {
> rtx chain;
>
> - /* Clobber the FP when we get here, so we have to make sure it's
> + /* Mark the FP as used when we get here, so we have to make sure it's
> marked as used by this function. */
> emit_use (hard_frame_pointer_rtx);
>
> @@ -907,17 +908,28 @@ expand_builtin_setjmp_receiver (rtx rece
> #ifdef HAVE_nonlocal_goto
> if (! HAVE_nonlocal_goto)
> #endif
> - {
> - emit_move_insn (virtual_stack_vars_rtx, hard_frame_pointer_rtx);
> - /* This might change the hard frame pointer in ways that aren't
> - apparent to early optimization passes, so force a clobber. */
> - emit_clobber (hard_frame_pointer_rtx);
> - }
> + /* First adjust our frame pointer to its actual value. It was
> + previously set to the start of the virtual area corresponding to
> + the stacked variables when we branched here and now needs to be
> + adjusted to the actual hardware fp value.
> +
> + Assignments to virtual registers are converted by
> + instantiate_virtual_regs into the corresponding assignment
> + to the underlying register (fp in this case) that makes
> + the original assignment true.
> + So the following insn will actually be decrementing fp by
> + STARTING_FRAME_OFFSET. */
> + emit_move_insn (virtual_stack_vars_rtx, hard_frame_pointer_rtx);
>
> #if !HARD_FRAME_POINTER_IS_ARG_POINTER
> if (fixed_regs[ARG_POINTER_REGNUM])
> {
> #ifdef ELIMINABLE_REGS
> + /* If the argument pointer can be eliminated in favor of the
> + frame pointer, we don't need to restore it. We assume here
> + that if such an elimination is present, it can always be used.
> + This is the case on all known machines; if we don't make this
> + assumption, we do unnecessary saving on many machines. */
> size_t i;
> static const struct elims {const int from, to;} elim_regs[] = ELIMINABLE_REGS;
>
> @@ -938,7 +950,7 @@ expand_builtin_setjmp_receiver (rtx rece
> #endif
>
> #ifdef HAVE_builtin_setjmp_receiver
> - if (HAVE_builtin_setjmp_receiver)
> + if (receiver_label != NULL && HAVE_builtin_setjmp_receiver)
> emit_insn (gen_builtin_setjmp_receiver (receiver_label));
> else
> #endif
> Index: gcc/stmt.c
> ===================================================================
> --- gcc/stmt.c (revision 192353)
> +++ gcc/stmt.c (working copy)
> @@ -102,7 +102,6 @@ typedef struct case_node *case_node_ptr;
>
> static int n_occurrences (int, const char *);
> static bool tree_conflicts_with_clobbers_p (tree, HARD_REG_SET *);
> -static void expand_nl_goto_receiver (void);
> static bool check_operand_nalternatives (tree, tree);
> static bool check_unique_operand_names (tree, tree, tree);
> static char *resolve_operand_name_1 (char *, tree, tree, tree);
> @@ -196,7 +195,7 @@ expand_label (tree label)
>
> if (DECL_NONLOCAL (label))
> {
> - expand_nl_goto_receiver ();
> + expand_builtin_setjmp_receiver (NULL);
> nonlocal_goto_handler_labels
> = gen_rtx_EXPR_LIST (VOIDmode, label_r,
> nonlocal_goto_handler_labels);
> @@ -1552,77 +1551,6 @@ expand_return (tree retval)
> }
> }
>
> -/* Emit code to restore vital registers at the beginning of a nonlocal goto
> - handler. */
> -static void
> -expand_nl_goto_receiver (void)
> -{
> - rtx chain;
> -
> - /* Clobber the FP when we get here, so we have to make sure it's
> - marked as used by this function. */
> - emit_use (hard_frame_pointer_rtx);
> -
> - /* Mark the static chain as clobbered here so life information
> - doesn't get messed up for it. */
> - chain = targetm.calls.static_chain (current_function_decl, true);
> - if (chain && REG_P (chain))
> - emit_clobber (chain);
> -
> -#ifdef HAVE_nonlocal_goto
> - if (! HAVE_nonlocal_goto)
> -#endif
> - /* First adjust our frame pointer to its actual value. It was
> - previously set to the start of the virtual area corresponding to
> - the stacked variables when we branched here and now needs to be
> - adjusted to the actual hardware fp value.
> -
> - Assignments are to virtual registers are converted by
> - instantiate_virtual_regs into the corresponding assignment
> - to the underlying register (fp in this case) that makes
> - the original assignment true.
> - So the following insn will actually be
> - decrementing fp by STARTING_FRAME_OFFSET. */
> - emit_move_insn (virtual_stack_vars_rtx, hard_frame_pointer_rtx);
> -
> -#if !HARD_FRAME_POINTER_IS_ARG_POINTER
> - if (fixed_regs[ARG_POINTER_REGNUM])
> - {
> -#ifdef ELIMINABLE_REGS
> - /* If the argument pointer can be eliminated in favor of the
> - frame pointer, we don't need to restore it. We assume here
> - that if such an elimination is present, it can always be used.
> - This is the case on all known machines; if we don't make this
> - assumption, we do unnecessary saving on many machines. */
> - static const struct elims {const int from, to;} elim_regs[] = ELIMINABLE_REGS;
> - size_t i;
> -
> - for (i = 0; i < ARRAY_SIZE (elim_regs); i++)
> - if (elim_regs[i].from == ARG_POINTER_REGNUM
> - && elim_regs[i].to == HARD_FRAME_POINTER_REGNUM)
> - break;
> -
> - if (i == ARRAY_SIZE (elim_regs))
> -#endif
> - {
> - /* Now restore our arg pointer from the address at which it
> - was saved in our stack frame. */
> - emit_move_insn (crtl->args.internal_arg_pointer,
> - copy_to_reg (get_arg_pointer_save_area ()));
> - }
> - }
> -#endif
> -
> -#ifdef HAVE_nonlocal_goto_receiver
> - if (HAVE_nonlocal_goto_receiver)
> - emit_insn (gen_nonlocal_goto_receiver ());
> -#endif
> -
> - /* We must not allow the code we just generated to be reordered by
> - scheduling. Specifically, the update of the frame pointer must
> - happen immediately, not later. */
> - emit_insn (gen_blockage ());
> -}
>
> /* Emit code to save the current value of stack. */
> rtx
> brgds, H-P
>