[PATCH] rs6000: Fix lost ud chains in swap optimization

[Bill Schmidt]

Hi,

We recently discovered a problem in swap optimization where the du- and 
ud-chains
were getting corrupted after a preliminary modification phase and prior to the
main body of the pass.  The fix for this is to rebuild the chains between 
phases.

Bootstrapped and tested on powerpc64le-unknown-linux-gnu with no regressions.
I've not included a test case because the problem tends to get lost in 
reduction,
and may shift over time anyway.  Is this okay for trunk, and eventual backport
to 8 and 7?

Thanks!

Bill


2019-03-07  Bill Schmidt  <wschm...@linux.ibm.com>

        * config/rs6000/rs6000-p8swap.c (rs6000_analyze_swaps): Rebuild
        ud- and du-chains between phases.


Index: gcc/config/rs6000/rs6000-p8swap.c
===================================================================
--- gcc/config/rs6000/rs6000-p8swap.c   (revision 269471)
+++ gcc/config/rs6000/rs6000-p8swap.c   (working copy)
@@ -2316,7 +2316,14 @@ rs6000_analyze_swaps (function *fun)
 
   /* Pre-pass to recombine lvx and stvx patterns so we don't lose info.  */
   recombine_lvx_stvx_patterns (fun);
+
+  /* Rebuild ud- and du-chains.  */
+  df_remove_problem (df_chain);
   df_process_deferred_rescans ();
+  df_set_flags (DF_RD_PRUNE_DEAD_DEFS);
+  df_chain_add_problem (DF_DU_CHAIN | DF_UD_CHAIN);
+  df_analyze ();
+  df_set_flags (DF_DEFER_INSN_RESCAN);
 
   /* Allocate structure to represent webs of insns.  */
   insn_entry = XCNEWVEC (swap_web_entry, get_max_uid ());