Fix 92085-2.c ICE due to having (const_int 0) as the destination of a set.

gcc/
	* lower-subreg.c (resolve_simple_move): If simplify_gen_subreg_concatn
	returns (const_int 0) for the destination, then emit nothing.

diff --git a/gcc/lower-subreg.c b/gcc/lower-subreg.c
index a11e535..abe7180 100644 (file)
--- a/gcc/lower-subreg.c
+++ b/gcc/lower-subreg.c
@@ -1087,12 +1087,21 @@ resolve_simple_move (rtx set, rtx_insn *insn)
        emit_clobber (dest);
 
       for (i = 0; i < words; ++i)
-       emit_move_insn (simplify_gen_subreg_concatn (word_mode, dest,
-                                                    dest_mode,
-                                                    i * UNITS_PER_WORD),
-                       simplify_gen_subreg_concatn (word_mode, src,
-                                                    orig_mode,
-                                                    i * UNITS_PER_WORD));
+       {
+         rtx t = simplify_gen_subreg_concatn (word_mode, dest,
+                                              dest_mode,
+                                              i * UNITS_PER_WORD);
+         /* simplify_gen_subreg_concatn can return (const_int 0) for
+            some sub-objects of paradoxical subregs.  As a source operand,
+            that's fine.  As a destination it must be avoided.  Those are
+            supposed to be don't care bits, so we can just drop that store
+            on the floor.  */
+         if (t != CONST0_RTX (word_mode))
+           emit_move_insn (t,
+                           simplify_gen_subreg_concatn (word_mode, src,
+                                                        orig_mode,
+                                                        i * UNITS_PER_WORD));
+       }
     }
 
   if (real_dest != NULL_RTX)