cse.c (fold_rtx): Update comments for (const (minus (label) (label))) case.

�
        * cse.c (fold_rtx): Update comments for (const (minus (label) (label)))
        case.
        (cse_insn): Avoid creating a bogus REG_EQUAL note for
        (const (minus (label) (label)))
        (record_jump_cond): Fix mismatched paren in comment.

From-SVN: r25490

diff --git a/gcc/cse.c b/gcc/cse.c
index 3b543f4ba699ef1d4f877d2a91b019663ddab991..cfcc4fac8efc0c3041a7b11cc49213b549e517bc 100644 (file)
--- a/gcc/cse.c
+++ b/gcc/cse.c
@@ -5167,7 +5167,11 @@ fold_rtx (x, insn)
                    /* Indicate this is a constant.  This isn't a 
                       valid form of CONST, but it will only be used
                       to fold the next insns and then discarded, so
-                      it should be safe.  */
+                      it should be safe.
+
+                      Note this expression must be explicitly discarded,
+                      by cse_insn, else it may end up in a REG_EQUAL note
+                      and "escape" to cause problems elsewhere.  */
                    return gen_rtx_CONST (GET_MODE (new), new);
                  }
              }
@@ -5913,7 +5917,7 @@ record_jump_cond (code, mode, op0, op1, reversed_nonequality)
   /* If OP0 and OP1 are known equal, and either is a paradoxical SUBREG,
      we know that they are also equal in the smaller mode (this is also
      true for all smaller modes whether or not there is a SUBREG, but
-     is not worth testing for with no SUBREG.  */
+     is not worth testing for with no SUBREG).  */
 
   /* Note that GET_MODE (op0) may not equal MODE.  */
   if (code == EQ && GET_CODE (op0) == SUBREG
@@ -7046,9 +7050,18 @@ cse_insn (insn, libcall_insn)
         equivalent constant, we want to add a REG_NOTE.   We don't want
         to write a REG_EQUAL note for a constant pseudo since verifying that
         that pseudo hasn't been eliminated is a pain.  Such a note also
-        won't help anything.  */
+        won't help anything. 
+
+        Avoid a REG_EQUAL note for (CONST (MINUS (LABEL_REF) (LABEL_REF)))
+        which can be created for a reference to a compile time computable
+        entry in a jump table.  */
+
       if (n_sets == 1 && src_const && GET_CODE (dest) == REG
-         && GET_CODE (src_const) != REG)
+         && GET_CODE (src_const) != REG
+         && ! (GET_CODE (src_const) == CONST
+               && GET_CODE (XEXP (src_const, 0)) == MINUS
+               && GET_CODE (XEXP (XEXP (src_const, 0), 0)) == LABEL_REF
+               && GET_CODE (XEXP (XEXP (src_const, 0), 1)) == LABEL_REF))
        {
          tem = find_reg_note (insn, REG_EQUAL, NULL_RTX);