diff --git a/gcc/combine.c b/gcc/combine.c
index cb5fa40..290a366 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -5903,7 +5903,8 @@ combine_simplify_rtx (rtx x, machine_mode op0_mode, int in_dest,
       if (HWI_COMPUTABLE_MODE_P (mode)
 	  && (STORE_FLAG_VALUE & ~GET_MODE_MASK (mode)) == 0
 	  && (temp = get_last_value (XEXP (x, 0)))
-	  && COMPARISON_P (temp))
+	  && COMPARISON_P (temp)
+	  && TRULY_NOOP_TRUNCATION_MODES_P (mode, GET_MODE (XEXP (x, 0))))
 	return gen_lowpart (mode, XEXP (x, 0));
       break;
 
diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
index c81e27e..e431e0c 100644
--- a/gcc/simplify-rtx.c
+++ b/gcc/simplify-rtx.c
@@ -1249,7 +1249,8 @@ simplify_context::simplify_unary_operation_1 (rtx_code code, machine_mode mode,
          than HOST_BITS_PER_WIDE_INT.  */
       if (HWI_COMPUTABLE_MODE_P (mode)
 	  && COMPARISON_P (op)
-	  && (STORE_FLAG_VALUE & ~GET_MODE_MASK (mode)) == 0)
+	  && (STORE_FLAG_VALUE & ~GET_MODE_MASK (mode)) == 0
+	  && TRULY_NOOP_TRUNCATION_MODES_P (mode, GET_MODE (op)))
 	{
 	  temp = rtl_hooks.gen_lowpart_no_emit (mode, op);
 	  if (temp)