Use a per-edge PRE PHI translation cache

This changes the phi translation cache to be per edge which
pushes it off the profiling radar.  For larger testcases the
combined hashtable causes a load of cache misses and making it
per edge allows to shrink the entry further.

2020-11-09  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/97765
	* tree-ssa-pre.c (bb_bitmap_sets::phi_translate_table): Add.
	(PHI_TRANS_TABLE): New macro.
	(phi_translate_table): Remove.
	(expr_pred_trans_d::pred): Remove.
	(expr_pred_trans_d::hash): Simplify.
	(expr_pred_trans_d::equal): Likewise.
	(phi_trans_add): Adjust.
	(phi_translate): Likewise.  Remove hash-table expansion
	detection and optimization.
	(phi_translate_set): Allocate PHI_TRANS_TABLE here.
	(init_pre): Adjsust.
	(fini_pre): Free PHI_TRANS_TABLE.