[PATCH] more PR33928: DIY dataflow in fwprop, to enable it at -O1 and speed it up at -O2

[Paolo Bonzini]

>> +static inline df_ref
>> +get_def_for_use (df_ref use)
> 
> Missing comment before function.

/* Return the only def in USE's use-def chain, or NULL if there is
   more than one def in the chain.  */

>> +static inline int
>> +bitmap_only_bit_between (const_bitmap b, unsigned first, unsigned last)
> 
> Missing comment before function.

/* Return the only bit between FIRST and LAST that is set in B,
   or -1 if there are zero or more than one such bits.  */

>> +static void
>> +process_uses (bitmap local_rd, df_ref *use_rec, int top_flag)
> 
> Missing comment before function.

/* Fill the use_def_ref vector with values for the uses in USE_REC,
   taking reaching definitions info from LOCAL_RD.  TOP_FLAG says
   which artificials uses should be used, when USE_REC is an
   artificial use vector.  */

>> +static void
>> +build_single_def_use_links (void)
> 
> Missing comment before function.

/* Do dataflow analysis and use reaching definitions to build
   a vector holding the reaching definitions of uses that have a
   single RD.  */

> I think Bernd will not be pleased (added to CC:), but I think this
> approach is the best thing we can do for the moment.

Yes, on the other hand with SSA expand probably we're better off marking
those things are TER-even-if-not-single-use, thus providing also a
better fix for PR39543.

Paolo