Cleanup --params for backward threader.

The new backward threader makes some of the --param knobs used to
control it questionable at best or no longer applicable at worst.

The fsm-maximum-phi-arguments param is unused and can be removed.

The max-fsm-thread-length param is block based which is a bit redundant,
since we already restrict paths based on instruction estimates.

The max-fsm-thread-paths restricts the total number of threadable paths
in a function.  We probably don't need this.  Besides, the forward
threader has no such restriction.

Tested on x86-64 Linux.

gcc/ChangeLog:

	* doc/invoke.texi: Remove max-fsm-thread-length,
	max-fsm-thread-paths, and fsm-maximum-phi-arguments.
	* params.opt: Same.
	* tree-ssa-threadbackward.c (back_threader::back_threader): Remove
	argument.
	(back_threader_registry::back_threader_registry): Same.
	(back_threader_profitability::profitable_path_p): Remove
	param_max_fsm_thread-length.
	(back_threader_registry::register_path): Remove
	m_max_allowable_paths.

gcc/doc/invoke.texi

@@ -14468,14 +14468,6 @@ Emit instrumentation calls to __tsan_func_entry() and __tsan_func_exit().
 Maximum number of instructions to copy when duplicating blocks on a
 finite state automaton jump thread path.
 
-@item max-fsm-thread-length
-Maximum number of basic blocks on a finite state automaton jump thread
-path.
-
-@item max-fsm-thread-paths
-Maximum number of new jump thread paths to create for a finite state
-automaton.
-
 @item parloops-chunk-size
 Chunk size of omp schedule for loops parallelized by parloops.
 
@@ -14630,10 +14622,6 @@ The maximum depth of recursive inlining for non-inline functions.
 Scale factor to apply to the number of statements in a threading path
 when comparing to the number of (scaled) blocks.
 
-@item fsm-maximum-phi-arguments
-Maximum number of arguments a PHI may have before the FSM threader
-will not try to thread through its block.
-
 @item uninit-control-dep-attempts
 Maximum number of nested calls to search for control dependencies
 during uninitialized variable analysis.

gcc/params.opt

@@ -173,10 +173,6 @@ Common Joined UInteger Var(param_ranger_logical_depth) Init(6) IntegerRange(1, 9
 Maximum depth of logical expression evaluation ranger will look through when
 evaluating outgoing edge ranges.
 
--param=fsm-maximum-phi-arguments=
-Common Joined UInteger Var(param_fsm_maximum_phi_arguments) Init(100) IntegerRange(1, 999999) Param Optimization
-Maximum number of arguments a PHI may have before the FSM threader will not try to thread through its block.
-
 -param=fsm-scale-path-blocks=
 Common Joined UInteger Var(param_fsm_scale_path_blocks) Init(3) IntegerRange(1, 10) Param Optimization
 Scale factor to apply to the number of blocks in a threading path when comparing to the number of (scaled) statements.
@@ -537,18 +533,10 @@ The maximum number of nested indirect inlining performed by early inliner.
 Common Joined UInteger Var(param_max_fields_for_field_sensitive) Param
 Maximum number of fields in a structure before pointer analysis treats the structure as a single variable.
 
--param=max-fsm-thread-length=
-Common Joined UInteger Var(param_max_fsm_thread_length) Init(10) IntegerRange(1, 999999) Param Optimization
-Maximum number of basic blocks on a finite state automaton jump thread path.
-
 -param=max-fsm-thread-path-insns=
 Common Joined UInteger Var(param_max_fsm_thread_path_insns) Init(100) IntegerRange(1, 999999) Param Optimization
 Maximum number of instructions to copy when duplicating blocks on a finite state automaton jump thread path.
 
--param=max-fsm-thread-paths=
-Common Joined UInteger Var(param_max_fsm_thread_paths) Init(50) IntegerRange(1, 999999) Param Optimization
-Maximum number of new jump thread paths to create for a finite state automaton.
-
 -param=max-gcse-insertion-ratio=
 Common Joined UInteger Var(param_max_gcse_insertion_ratio) Init(20) Param Optimization
 The maximum ratio of insertions to deletions of expressions in GCSE.

gcc/tree-ssa-threadbackward.c

@@ -52,12 +52,11 @@ along with GCC; see the file COPYING3.  If not see
 class back_threader_registry
 {
 public:
-  back_threader_registry (int max_allowable_paths);
+  back_threader_registry ();
   bool register_path (const vec<basic_block> &, edge taken);
   bool thread_through_all_blocks (bool may_peel_loop_headers);
 private:
   back_jt_path_registry m_lowlevel_registry;
-  const int m_max_allowable_paths;
   int m_threaded_paths;
 };
 
@@ -120,8 +119,7 @@ private:
 const edge back_threader::UNREACHABLE_EDGE = (edge) -1;
 
 back_threader::back_threader (bool speed_p)
-  : m_registry (param_max_fsm_thread_paths),
-    m_profit (speed_p),
+  : m_profit (speed_p),
     m_solver (m_ranger, /*resolve=*/false)
 {
   m_last_stmt = NULL;
@@ -547,8 +545,7 @@ back_threader::debug ()
   dump (stderr);
 }
 
-back_threader_registry::back_threader_registry (int max_allowable_paths)
-  : m_max_allowable_paths (max_allowable_paths)
+back_threader_registry::back_threader_registry ()
 {
   m_threaded_paths = 0;
 }
@@ -594,15 +591,6 @@ back_threader_profitability::profitable_path_p (const vec<basic_block> &m_path,
   if (m_path.length () <= 1)
       return false;
 
-  if (m_path.length () > (unsigned) param_max_fsm_thread_length)
-    {
-      if (dump_file && (dump_flags & TDF_DETAILS))
-	fprintf (dump_file, "  FAIL: Jump-thread path not considered: "
-		 "the number of basic blocks on the path "
-		 "exceeds PARAM_MAX_FSM_THREAD_LENGTH.\n");
-      return false;
-    }
-
   int n_insns = 0;
   gimple_stmt_iterator gsi;
   loop_p loop = m_path[0]->loop_father;
@@ -885,15 +873,6 @@ bool
 back_threader_registry::register_path (const vec<basic_block> &m_path,
 				       edge taken_edge)
 {
-  if (m_threaded_paths > m_max_allowable_paths)
-    {
-      if (dump_file && (dump_flags & TDF_DETAILS))
-	fprintf (dump_file, "  FAIL: Jump-thread path not considered: "
-		 "the number of previously recorded paths to "
-		 "thread exceeds PARAM_MAX_FSM_THREAD_PATHS.\n");
-      return false;
-    }
-
   vec<jump_thread_edge *> *jump_thread_path
     = m_lowlevel_registry.allocate_thread_path ();