[Bug rtl-optimization/33224] failing rtl iv analysis (maybe due to df)

["dorit at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #5 from dorit at gcc dot gnu dot org  2007-08-30 16:29 -------
> dorit,
> i am having trouble exactly reproducing this example because you did not
> give the svn revision and so all of the numbers are a little bit
> different. 

it's revision 127623

> However, I am going to submit a patch which improves the dump
> information a lot for these passes and we should talk about it after we
> can get on the same page.

I applied your patch, and I'll send you the dump shorlty.

> However, from looking at your posting, there are some issues that you
> may want to look at before we talk:
> The reaching defs problem makes a scan for all of the defs in the blocks
> in the region.  Once all of the defs are found, they are sorted where
> the primary key is the regno. 
> The id's (DF_REF_ID) are then assigned based on this sorting.  The
> reaching defs problem actually depends on all of the defs for a regno to
> be contigious.
> The DF_REF_IDs are not stable between calls to df_set_blocks and any def
> outside of the region has an undefined DF_REF_ID.
> In your posting you have:
> > Below is the output of df_ref_debug for adef in each iteration of the loop in
> > latch_dominating_def:
> > d40 reg 187 bb 3 insn 255 flag 0x0 type 0x0 loc 0xf7da4608(0xf7d9a4e0) chain { }
> > d93 reg 187 bb 2 insn 40 flag 0x0 type 0x0 loc 0xf7d89cc8(0xf7d9a4e0) chain { }
> The number after the first "d" is the DF_REF_ID.  Note that they are not
> contiguous. 
> Given the sorting that occurred, they must be contiguous.  I assume from this
> that 
> someone is holding on to old id's.  This is not correct.
> If you are going to play the game with df_set_blocks, you are allowed to hold
> onto a 
> def, but not the DF_REF_ID, you cannot look at the DF_REF_ID for a def 
> that is not in the blocks set by df_set_blocks.   

are you saying it's safer not to call df_set_blocks in iv_analysis_loop_init?
(iv-analysis still fails when I do that, but maybe that in turn requires other
changes?)


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33224