Remove no-op register to register copies in CSE just like we remove no-op memory to memory copies.

        PR rtl-optimization/90275
        * cse.c (cse_insn): Delete no-op register moves too.

        PR rtl-optimization/90275
        * gcc.c-torture/compile/pr90275.c: New test.

gcc/ChangeLog

+2020-03-12  Richard Sandiford  <richard.sandiford@arm.com>
+
+	PR rtl-optimization/90275
+	* cse.c (cse_insn): Delete no-op register moves too.
+
 2020-03-12  Darius Galis  <darius.galis@cyberthorstudios.com>
 
 	* config/rx/rx.md (CTRLREG_CPEN): Remove.

gcc/cse.c

@@ -4625,7 +4625,7 @@ cse_insn (rtx_insn *insn)
   for (i = 0; i < n_sets; i++)
     {
       bool repeat = false;
-      bool mem_noop_insn = false;
+      bool noop_insn = false;
       rtx src, dest;
       rtx src_folded;
       struct table_elt *elt = 0, *p;
@@ -5324,9 +5324,11 @@ cse_insn (rtx_insn *insn)
 	    }
 
 	  /* Similarly, lots of targets don't allow no-op
-	     (set (mem x) (mem x)) moves.  */
+	     (set (mem x) (mem x)) moves.  Even (set (reg x) (reg x))
+	     might be impossible for certain registers (like CC registers).  */
 	  else if (n_sets == 1
-		   && MEM_P (trial)
+		   && !CALL_P (insn)
+		   && (MEM_P (trial) || REG_P (trial))
 		   && MEM_P (dest)
 		   && rtx_equal_p (trial, dest)
 		   && !side_effects_p (dest)
@@ -5334,7 +5336,7 @@ cse_insn (rtx_insn *insn)
 		       || insn_nothrow_p (insn)))
 	    {
 	      SET_SRC (sets[i].rtl) = trial;
-	      mem_noop_insn = true;
+	      noop_insn = true;
 	      break;
 	    }
 
@@ -5562,8 +5564,8 @@ cse_insn (rtx_insn *insn)
 	  sets[i].rtl = 0;
 	}
 
-      /* Similarly for no-op MEM moves.  */
-      else if (mem_noop_insn)
+      /* Similarly for no-op moves.  */
+      else if (noop_insn)
 	{
 	  if (cfun->can_throw_non_call_exceptions && can_throw_internal (insn))
 	    cse_cfg_altered = true;

gcc/testsuite/ChangeLog

+2020-03-12  Jeff Law  <law@redhat.com>
+
+	PR rtl-optimization/90275
+	* gcc.c-torture/compile/pr90275.c: New test.
+
 2020-03-12  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/94103

gcc/testsuite/gcc.c-torture/compile/pr90275.c

+a, b, c;
+
+long long d;
+
+e() {
+
+  char f;
+
+  for (;;) {
+
+    c = a = c ? 5 : 0;
+
+    if (f) {
+
+      b = a;
+
+      f = d;
+
+    }
+
+    (d || b) < (a > e) ?: (b ? 0 : f) || (d -= f);
+
+  }
+
+}
+
+