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Re: Fix a case where combine generates noncanonical debug rtl
Richard Sandiford writes:
> Mikael Pettersson <mikpe@it.uu.se> writes:
> > Richard Sandiford writes:
> > > Eric Botcazou <ebotcazou@adacore.com> writes:
> > > >> Sorry, I should have mentioned this (because I did check!). The only
> > > >> use of i2src that isn't conditional on MAY_HAVE_DEBUG_INSNS is for calls,
> > > >> and find_split_point doesn't try to split those.
> > > >
> > > > Fair enough. Then set i2src in an 'else' branch to a piece of RTL that would
> > > > cause the compiler to blow up if ever touched later (e.g. some virtual_*_rtx)
> > > > with a small blurb in the comment. OK with this change.
> > >
> > > Using virtual_*_rtx seemed a bit non-obvious, so I just went for NULL
> > > and asserted that i2src was indeed nonnull in the call code. Here's
> > > what I installed after bootstrapping & regression-testing on
> > > x86_64-linux-gnu.
> > >
> > > Richard
> > >
> > > gcc/
> > > * combine.c (propagate_for_debug): Call make_compound_operation
> > > on the source value.
> > > (try_combine): When implementing a split chosen by find_split_point,
> > > either copy i2src or set it to null. Assert that i2src is not null
> > > before substituting into CALL_INSN_FUNCTION_USAGE.
> >
> > This (r159600) triggered a bootstrap failure with trunk on sparc64-linux:
> > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44255
> >
> > (ARM sees the identical bootstrap failure, but I haven't yet verified
> > that the same commit is the cause.)
>
> Sorry for the breakage. It'll probably be hard to track this down
> without access to the targets involved, but it'd be interesting to
> know if reverting this hunk:
>
> @@ -3294,6 +3301,11 @@ try_combine (rtx i3, rtx i2, rtx i1, int
>
> i2scratch = true;
>
> + /* *SUBST may be part of I2SRC, so make sure we have the
> + original expression around for later debug processing. */
> + if (MAY_HAVE_DEBUG_INSNS)
> + i2src = copy_rtx (i2src);
> +
> /* Get NEWDEST as a register in the proper mode. We have already
> validated that we can do this. */
> if (GET_MODE (i2dest) != split_mode && split_mode != VOIDmode)
>
> makes the problem go away.
That was in your original patch, but the version you committed is
slightly different. I'm currently trying to bootstrap with the patch
below applied.
/Mikael
--- gcc-4.6-20100522/gcc/combine.c.~1~ 2010-05-21 15:53:22.000000000 +0200
+++ gcc-4.6-20100522/gcc/combine.c 2010-05-24 21:04:33.000000000 +0200
@@ -3303,10 +3303,12 @@ try_combine (rtx i3, rtx i2, rtx i1, int
/* *SPLIT may be part of I2SRC, so make sure we have the
original expression around for later debug processing.
We should not need I2SRC any more in other cases. */
+#if 0
if (MAY_HAVE_DEBUG_INSNS)
i2src = copy_rtx (i2src);
else
i2src = NULL;
+#endif
/* Get NEWDEST as a register in the proper mode. We have already
validated that we can do this. */