diff --git a/gcc/ree.cc b/gcc/ree.cc
index 413aec7c8eb..33c803f16ce 100644
--- a/gcc/ree.cc
+++ b/gcc/ree.cc
@@ -473,7 +473,8 @@ get_defs (rtx_insn *insn, rtx reg, vec<rtx_insn *> *dest)
 	break;
     }
 
-  gcc_assert (use != NULL);
+  if (use == NULL)
+    return NULL;
 
   ref_chain = DF_REF_CHAIN (use);
 
@@ -514,7 +515,8 @@ get_uses (rtx_insn *insn, rtx reg)
     if (REGNO (DF_REF_REG (def)) == REGNO (reg))
       break;
 
-  gcc_assert (def != NULL);
+  if (def == NULL)
+    return NULL;
 
   ref_chain = DF_REF_CHAIN (def);
 
@@ -771,6 +773,58 @@ combine_reaching_defs (ext_cand *cand, const_rtx set_pat, ext_state *state)
   state->defs_list.truncate (0);
   state->copies_list.truncate (0);
 
+  if (cand->code == ZERO_EXTEND)
+    {
+      rtx orig_src = XEXP (SET_SRC (cand->expr),0);
+      rtx set = single_set (cand->insn);
+
+      if (!set)
+	return false;
+
+      machine_mode ext_dst_mode = GET_MODE (SET_DEST (set));
+
+      if (!get_defs (cand->insn, orig_src, NULL))
+	{
+	   bool copy_needed
+	     = (REGNO (SET_DEST (cand->expr)) != REGNO (XEXP (SET_SRC (cand->expr), 0)));
+
+	  if (!copy_needed && ext_dst_mode != GET_MODE (orig_src)
+	      && FUNCTION_ARG_REGNO_P (REGNO (orig_src))
+	      && !FUNCTION_VALUE_REGNO_P (REGNO (orig_src)))
+	     {
+		if (side_effects_p (PATTERN (cand->insn)))
+		  return false;
+
+		struct df_link *uses
+		  = get_uses (cand->insn, SET_DEST (PATTERN (cand->insn)));
+
+		if (!uses) return false;
+
+		for (df_link *use = uses; use; use = use->next)
+		  {
+		    if (!use->ref)
+		      return false;
+
+		    if (BLOCK_FOR_INSN (cand->insn)
+			!= BLOCK_FOR_INSN (DF_REF_INSN (use->ref)))
+		      return false;
+
+		    rtx_insn *insn = DF_REF_INSN (use->ref);
+
+		    if (GET_CODE (PATTERN (insn)) == SET)
+		      {
+			rtx_code code = GET_CODE (SET_SRC (PATTERN (insn)));
+			if (GET_RTX_CLASS (code) == RTX_BIN_ARITH
+			    || GET_RTX_CLASS (code) == RTX_COMM_ARITH
+			    || GET_RTX_CLASS (code) == RTX_UNARY)
+			  return false;
+		       }
+		    }
+		 return true;
+	     }
+	 }
+    }
+
   outcome = make_defs_and_copies_lists (cand->insn, set_pat, state);
 
   if (!outcome)
@@ -1112,26 +1166,35 @@ add_removable_extension (const_rtx expr, rtx_insn *insn,
       rtx reg = XEXP (src, 0);
       struct df_link *defs, *def;
       ext_cand *cand;
+      defs = get_defs (insn, reg, NULL);
 
       /* Zero-extension of an undefined value is partly defined (it's
 	 completely undefined for sign-extension, though).  So if there exists
 	 a path from the entry to this zero-extension that leaves this register
 	 uninitialized, removing the extension could change the behavior of
 	 correct programs.  So first, check it is not the case.  */
-      if (code == ZERO_EXTEND && !bitmap_bit_p (init_regs, REGNO (reg)))
+      if (!defs && code == ZERO_EXTEND && FUNCTION_ARG_REGNO_P (REGNO (reg)))
 	{
-	  if (dump_file)
-	    {
-	      fprintf (dump_file, "Cannot eliminate extension:\n");
-	      print_rtl_single (dump_file, insn);
-	      fprintf (dump_file, " because it can operate on uninitialized"
-			          " data\n");
-	    }
+	  ext_cand e = {expr, code, mode, insn};
+	  insn_list->safe_push (e);
 	  return;
 	}
 
+
+       if ((code == ZERO_EXTEND
+	    && !bitmap_bit_p (init_regs, REGNO (reg))))
+	  {
+	    if (dump_file)
+	      {
+		fprintf (dump_file, "Cannot eliminate extension:\n");
+		print_rtl_single (dump_file, insn);
+		fprintf (dump_file, " because it can operate on uninitialized"
+				    " data\n");
+	      }
+	    return;
+	  }
+
       /* Second, make sure we can get all the reaching definitions.  */
-      defs = get_defs (insn, reg, NULL);
       if (!defs)
 	{
 	  if (dump_file)
@@ -1321,7 +1384,8 @@ find_and_remove_re (void)
 	      && (REGNO (SET_DEST (set)) != REGNO (XEXP (SET_SRC (set), 0))))
 	    {
               reinsn_copy_list.safe_push (curr_cand->insn);
-              reinsn_copy_list.safe_push (state.defs_list[0]);
+	      if (state.defs_list.length() != 0)
+		reinsn_copy_list.safe_push (state.defs_list[0]);
 	    }
 	  reinsn_del_list.safe_push (curr_cand->insn);
 	  state.modified[INSN_UID (curr_cand->insn)].deleted = 1;
@@ -1342,24 +1406,27 @@ find_and_remove_re (void)
      Remember that the memory reference will be changed to refer to the
      destination of the extention.  So we're actually emitting a copy
      from the new destination to the old destination.  */
-  for (unsigned int i = 0; i < reinsn_copy_list.length (); i += 2)
-    {
-      rtx_insn *curr_insn = reinsn_copy_list[i];
-      rtx_insn *def_insn = reinsn_copy_list[i + 1];
-
-      /* Use the mode of the destination of the defining insn
-	 for the mode of the copy.  This is necessary if the
-	 defining insn was used to eliminate a second extension
-	 that was wider than the first.  */
-      rtx sub_rtx = *get_sub_rtx (def_insn);
-      rtx set = single_set (curr_insn);
-      rtx new_dst = gen_rtx_REG (GET_MODE (SET_DEST (sub_rtx)),
-				 REGNO (XEXP (SET_SRC (set), 0)));
-      rtx new_src = gen_rtx_REG (GET_MODE (SET_DEST (sub_rtx)),
-				 REGNO (SET_DEST (set)));
-      rtx new_set = gen_rtx_SET (new_dst, new_src);
-      emit_insn_after (new_set, def_insn);
-    }
+   for (unsigned int i = 0; i < reinsn_copy_list.length (); i += 2)
+     {
+       rtx_insn *curr_insn = reinsn_copy_list[i];
+
+       if ((i+1) < reinsn_copy_list.length())
+	 {
+	   rtx_insn *def_insn = reinsn_copy_list[i + 1];
+	   /* Use the mode of the destination of the defining insn
+	      for the mode of the copy.  This is necessary if the
+	      defining insn was used to eliminate a second extension
+	      that was wider than the first.  */
+	   rtx sub_rtx = *get_sub_rtx (def_insn);
+	   rtx set = single_set (curr_insn);
+	   rtx new_dst = gen_rtx_REG (GET_MODE (SET_DEST (sub_rtx)),
+				      REGNO (XEXP (SET_SRC (set), 0)));
+	   rtx new_src = gen_rtx_REG (GET_MODE (SET_DEST (sub_rtx)),
+				      REGNO (SET_DEST (set)));
+	   rtx new_set = gen_rtx_SET (new_dst, new_src);
+	   emit_insn_after (new_set, def_insn);
+	}
+      }
 
   /* Delete all useless extensions here in one sweep.  */
   FOR_EACH_VEC_ELT (reinsn_del_list, i, curr_insn)
diff --git a/gcc/testsuite/g++.target/powerpc/zext-elim-3.C b/gcc/testsuite/g++.target/powerpc/zext-elim-3.C
new file mode 100644
index 00000000000..1d443af066a
--- /dev/null
+++ b/gcc/testsuite/g++.target/powerpc/zext-elim-3.C
@@ -0,0 +1,16 @@
+/* { dg-do compile { target { powerpc*-*-* } } } */
+/* { dg-require-effective-target lp64 } */
+/* { dg-require-effective-target powerpc_p9vector_ok } */
+/* { dg-options "-mcpu=power9 -O2 -free" } */
+
+void *memset(void *b, int c, unsigned long len)
+{
+  unsigned long i;
+
+  for (i = 0; i < len; i++)
+    ((unsigned char *)b)[i] = c;
+
+   return b;
+}
+
+/* { dg-final { scan-assembler-not "rlwinm" } } */
