[PATCH] In the pipeline, UNRECOG INSN is not executed in advance if it starts a live range.

[Jin Ma <jinma@linux.alibaba.com>]

  Unrecog insns (such as CLOBBER, USE) does not represent real instructions, but in the
process of pipeline optimization, they will wait for transmission in ready list like
other insns, without considering resource conflicts and cycles. This results in a
multi-issue CPU architecture that can be issued at any time if other regular insns
have resource conflicts or cannot be launched for other reasons. As a result, its
position is advanced in the generated insns sequence, which will affect register
allocation and often lead to more redundant mov instructions.

A simple example:
https://github.com/majin2020/gcc-test/blob/master/test.c
This is a function in the dhrystone benchmark.

https://github.com/majin2020/gcc-test/blob/0b08c1a13de9663d7d9aba7539b960ec0607ca24/test.c.299r.sched1
This is a log of the pass 'sched1' When issue_rate == 2. Among them, insn 13 and 14 are
much ahead of schedule, which risks generating redundant mov instructions, which seems
unreasonable.

Therefore, I submit patch again on the basis of the last review opinions to try to solve
this problem.

This is the new log of shed1 after patch is added.
https://github.com/majin2020/gcc-test/commit/efcb43e3369e771bde702955048bfe3f501263dd

gcc/ChangeLog:

        * haifa-sched.cc (unrecog_insn_for_forw_only_p): New.
        (prune_ready_list): UNRECOG INSN is not executed in advance if it starts a
	live range.
---
 gcc/haifa-sched.cc | 44 +++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 39 insertions(+), 5 deletions(-)

diff --git a/gcc/haifa-sched.cc b/gcc/haifa-sched.cc
index 2c881ede0ec..205680a4936 100644
--- a/gcc/haifa-sched.cc
+++ b/gcc/haifa-sched.cc
@@ -765,6 +765,23 @@ real_insn_for_shadow (rtx_insn *insn)
   return pair->i1;
 }
 
+/* Return true if INSN is unrecog that starts a live range.  */
+
+static bool
+unrecog_insn_for_forw_only_p (rtx_insn *insn)
+{
+  if (insn && !INSN_P (insn) && recog_memoized (insn) >= 0)
+    return false;
+
+  if ((GET_CODE (PATTERN (insn)) == CLOBBER
+       || GET_CODE (PATTERN (insn)) == USE)
+      && !sd_lists_empty_p (insn, SD_LIST_FORW)
+      && sd_lists_empty_p (insn, SD_LIST_BACK))
+    return true;
+
+  return false;
+}
+
 /* For a pair P of insns, return the fixed distance in cycles from the first
    insn after which the second must be scheduled.  */
 static int
@@ -6320,11 +6337,28 @@ prune_ready_list (state_t temp_state, bool first_cycle_insn_p,
 	    }
 	  else if (recog_memoized (insn) < 0)
 	    {
-	      if (!first_cycle_insn_p
-		  && (GET_CODE (PATTERN (insn)) == ASM_INPUT
-		      || asm_noperands (PATTERN (insn)) >= 0))
-		cost = 1;
-	      reason = "asm";
+	      if (GET_CODE (PATTERN (insn)) == ASM_INPUT
+		  || asm_noperands (PATTERN (insn)) >= 0)
+		{
+		  reason = "asm";
+		  if (!first_cycle_insn_p)
+		    cost = 1;
+		}
+	      else if (unrecog_insn_for_forw_only_p (insn))
+		{
+		  reason = "unrecog insn";
+		  if (!first_cycle_insn_p)
+		    cost = 1;
+		  else
+		    {
+		      int j = i;
+		      while (n > ++j)
+			if (!unrecog_insn_for_forw_only_p (ready_element (&ready, j)))
+			  break;
+
+		      cost = (j == n) ? 0 : 1;
+		    }
+		}
 	    }
 	  else if (sched_pressure != SCHED_PRESSURE_NONE)
 	    {
-- 
2.17.1