re PR target/70574 (wrong code with -mavx2, read of partially initialised stack variable)

	PR rtl-optimization/70574
	* fwprop.c (forward_propagate_and_simplify): Don't add
	REG_EQUAL note if DF_REF_REG (use) is a paradoxical subreg.
	(try_fwprop_subst): Don't add REG_EQUAL note if there are any
	paradoxical subregs within *loc.

	* gcc.target/i386/avx2-pr70574.c: New test.

From-SVN: r234833

1 files changed, 27 insertions, 5 deletions

diff --git a/gcc/fwprop.c b/gcc/fwprop.c
index c4587d7..d8cb9fa 100644
--- a/gcc/fwprop.c
+++ b/gcc/fwprop.c
@@ -999,10 +999,27 @@ try_fwprop_subst (df_ref use, rtx *loc, rtx new_rtx, rtx_insn *def_insn,
 	 making a new one if one does not already exist.  */
       if (set_reg_equal)
 	{
-	  if (dump_file)
-	    fprintf (dump_file, " Setting REG_EQUAL note\n");
+	  /* If there are any paradoxical SUBREGs, don't add REG_EQUAL note,
+	     because the bits in there can be anything and so might not
+	     match the REG_EQUAL note content.  See PR70574.  */
+	  subrtx_var_iterator::array_type array;
+	  FOR_EACH_SUBRTX_VAR (iter, array, *loc, NONCONST)
+	    {
+	      rtx x = *iter;
+	      if (SUBREG_P (x) && paradoxical_subreg_p (x))
+		{
+		  set_reg_equal = false;
+		  break;
+		}
+	    }
 
-	  note = set_unique_reg_note (insn, REG_EQUAL, copy_rtx (new_rtx));
+	  if (set_reg_equal)
+	    {
+	      if (dump_file)
+		fprintf (dump_file, " Setting REG_EQUAL note\n");
+
+	      note = set_unique_reg_note (insn, REG_EQUAL, copy_rtx (new_rtx));
+	    }
 	}
     }
 
@@ -1300,14 +1317,19 @@ forward_propagate_and_simplify (df_ref use, rtx_insn *def_insn, rtx def_set)
 	 that isn't mentioned in USE_SET, as the note would be invalid
 	 otherwise.  We also don't want to install a note if we are merely
 	 propagating a pseudo since verifying that this pseudo isn't dead
-	 is a pain; moreover such a note won't help anything.  */
+	 is a pain; moreover such a note won't help anything.
+	 If the use is a paradoxical subreg, make sure we don't add a
+	 REG_EQUAL note for it, because it is not equivalent, it is one
+	 possible value for it, but we can't rely on it holding that value.
+	 See PR70574.  */
       set_reg_equal = (note == NULL_RTX
 		       && REG_P (SET_DEST (use_set))
 		       && !REG_P (src)
 		       && !(GET_CODE (src) == SUBREG
 			    && REG_P (SUBREG_REG (src)))
 		       && !reg_mentioned_p (SET_DEST (use_set),
-					    SET_SRC (use_set)));
+					    SET_SRC (use_set))
+		       && !paradoxical_subreg_p (DF_REF_REG (use)));
     }
 
   if (GET_MODE (*loc) == VOIDmode)