Index: config/rs6000/rs6000.c
===================================================================
--- config/rs6000/rs6000.c	(revision 248140)
+++ config/rs6000/rs6000.c	(working copy)
@@ -28372,7 +28372,21 @@ rs6000_emit_allocate_stack (HOST_WIDE_IN
 	  && REGNO (stack_limit_rtx) > 1
 	  && REGNO (stack_limit_rtx) <= 31)
 	{
-	  emit_insn (gen_add3_insn (tmp_reg, stack_limit_rtx, GEN_INT (size)));
+	  rtx cst = GEN_INT (size);
+
+	  /* The add expander doesn't correctly handle r0.  */
+	  if (satisfies_constraint_I (cst))
+	    emit_insn (gen_rtx_SET (tmp_reg,
+				    gen_rtx_PLUS (Pmode, stack_limit_rtx,
+						  cst)));
+	  else
+	    {
+	      emit_move_insn (tmp_reg, cst);
+	      emit_insn (gen_rtx_SET (tmp_reg,
+				      gen_rtx_PLUS (Pmode, stack_limit_rtx,
+						    tmp_reg)));
+	    }
+
 	  emit_insn (gen_cond_trap (LTU, stack_reg, tmp_reg,
 				    const0_rtx));
 	}