1 files changed, 5 insertions, 1 deletions
diff --git a/gcc/cse.c b/gcc/cse.c
index 0ad7b2e..9f4e979 100644
--- a/gcc/cse.c
+++ b/gcc/cse.c
@@ -3786,8 +3786,12 @@ equiv_constant (rtx x)
 	    }
 	}
 
-      /* Otherwise see if we already have a constant for the inner REG.  */
+      /* Otherwise see if we already have a constant for the inner REG,
+	 and if that is enough to calculate an equivalent constant for
+	 the subreg.  Note that the upper bits of paradoxical subregs
+	 are undefined, so they cannot be said to equal anything.  */
       if (REG_P (SUBREG_REG (x))
+	  && GET_MODE_SIZE (mode) <= GET_MODE_SIZE (imode)
 	  && (new_rtx = equiv_constant (SUBREG_REG (x))) != 0)
         return simplify_subreg (mode, new_rtx, imode, SUBREG_BYTE (x));