[Bug debug/106746] [13 Regression] '-fcompare-debug' failure (length) with -O2 -fsched2-use-superblocks since r13-2041-g6624ad73064de241

["hjl.tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106746

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |richard.sandiford at arm dot com,
                   |                            |roger at nextmovesoftware dot com,
                   |                            |segher at kernel dot crashing.org

--- Comment #6 from H.J. Lu <hjl.tools at gmail dot com> ---
Revert

diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc
index fa20665bb01..7d09bf7103d 100644
--- a/gcc/simplify-rtx.cc
+++ b/gcc/simplify-rtx.cc
@@ -1615,6 +1639,24 @@ simplify_context::simplify_unary_operation_1 (rtx_code
co
de, machine_mode mode,
            }
        }

+      /* We can canonicalize SIGN_EXTEND (op) as ZERO_EXTEND (op) when
+         we know the sign bit of OP must be clear.  */
+      if (val_signbit_known_clear_p (GET_MODE (op),
+                                    nonzero_bits (op, GET_MODE (op))))
+       return simplify_gen_unary (ZERO_EXTEND, mode, op, GET_MODE (op));
+
+      /* (sign_extend:DI (subreg:SI (ctz:DI ...))) is (ctz:DI ...).  */
+      if (GET_CODE (op) == SUBREG
+         && subreg_lowpart_p (op)
+         && GET_MODE (SUBREG_REG (op)) == mode
+         && is_a <scalar_int_mode> (mode, &int_mode)
+         && is_a <scalar_int_mode> (GET_MODE (op), &op_mode)
+         && GET_MODE_PRECISION (int_mode) <= HOST_BITS_PER_WIDE_INT
+         && GET_MODE_PRECISION (op_mode) < GET_MODE_PRECISION (int_mode)
+         && (nonzero_bits (SUBREG_REG (op), mode)
+             & ~(GET_MODE_MASK (op_mode) >> 1)) == 0)
+       return SUBREG_REG (op);
+
 #if defined(POINTERS_EXTEND_UNSIGNED)
       /* As we do not know which address space the pointer is referring to,
         we can do this only if the target does not support different pointer

fixes the failure.