rtl-optimization/98144 - tame REE memory usage

This changes the REE dataflow to change the explicit all-ones
starting solution to be implicit via a visited flag, removing
the need to initially start with fully populated bitmaps for
all basic-blocks.  That reduces peak memory use when compiling
the RTL checking enabled insn-extract.c testcase from PR98144
from 6GB to less than 2GB.

2021-01-29  Richard Biener  <rguenther@suse.de>

	PR rtl-optimization/98144
	* df.h (df_mir_bb_info): Add con_visited member.
	* df-problems.c (df_mir_alloc): Initialize con_visited,
	do not fully populate IN and OUT.
	(df_mir_reset): Likewise.
	(df_mir_confluence_0): Set con_visited.
	(df_mir_confluence_n): Properly handle implicitely
	fully populated IN and OUT as designated by con_visited
	and update con_visited accordingly.

1 files changed, 1 insertions, 0 deletions

diff --git a/gcc/df.h b/gcc/df.h
index 88d35e4..5effefa 100644
--- a/gcc/df.h
+++ b/gcc/df.h
@@ -929,6 +929,7 @@ public:
   /* The results of the dataflow problem.  */
   bitmap_head in;    /* At the top of the block.  */
   bitmap_head out;   /* At the bottom of the block.  */
+  bool con_visited;  /* Visited by con_fun_{0,n}.  */
 };