(num_sign_bit_copies): Can handle paradoxical subreg only

if LOAD_EXTEND_OP is defined to SIGN_EXTEND.

From-SVN: r8787

diff --git a/gcc/combine.c b/gcc/combine.c
index d7248bf610fa4127798e17451fafd8635c928f60..3a16a70f06cca979d703eb6f0fd58f4c16f2a147 100644 (file)
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -7139,14 +7139,22 @@ num_sign_bit_copies (x, mode)
        }
 
 #ifdef WORD_REGISTER_OPERATIONS
+#ifdef LOAD_EXTEND_OP
       /* For paradoxical SUBREGs on machines where all register operations
         affect the entire register, just look inside.  Note that we are
         passing MODE to the recursive call, so the number of sign bit copies
         will remain relative to that mode, not the inner mode.  */
 
-      if (GET_MODE_SIZE (GET_MODE (x))
-         > GET_MODE_SIZE (GET_MODE (SUBREG_REG (x))))
+      /* This works only if loads sign extend.  Otherwise, if we get a
+        reload for the inner part, it may be loaded from the stack, and
+        then we lose all sign bit copies that existed before the store
+        to the stack.  */
+
+      if ((GET_MODE_SIZE (GET_MODE (x))
+          > GET_MODE_SIZE (GET_MODE (SUBREG_REG (x))))
+         && LOAD_EXTEND_OP (GET_MODE (SUBREG_REG (x))) == SIGN_EXTEND)
        return num_sign_bit_copies (SUBREG_REG (x), mode);
+#endif
 #endif
       break;