+static void delete_computation (rtx insn);
+
+/* Recursively delete prior insns that compute the value (used only by INSN
+ which the caller is deleting) stored in the register mentioned by NOTE
+ which is a REG_DEAD note associated with INSN. */
+
+static void
+delete_prior_computation (rtx note, rtx insn)
+{
+ rtx our_prev;
+ rtx reg = XEXP (note, 0);
+
+ for (our_prev = prev_nonnote_insn (insn);
+ our_prev && (NONJUMP_INSN_P (our_prev)
+ || CALL_P (our_prev));
+ our_prev = prev_nonnote_insn (our_prev))
+ {
+ rtx pat = PATTERN (our_prev);
+
+ /* If we reach a CALL which is not calling a const function
+ or the callee pops the arguments, then give up. */
+ if (CALL_P (our_prev)
+ && (! RTL_CONST_CALL_P (our_prev)
+ || GET_CODE (pat) != SET || GET_CODE (SET_SRC (pat)) != CALL))
+ break;
+
+ /* If we reach a SEQUENCE, it is too complex to try to
+ do anything with it, so give up. We can be run during
+ and after reorg, so SEQUENCE rtl can legitimately show
+ up here. */
+ if (GET_CODE (pat) == SEQUENCE)
+ break;
+
+ if (GET_CODE (pat) == USE
+ && NONJUMP_INSN_P (XEXP (pat, 0)))
+ /* reorg creates USEs that look like this. We leave them
+ alone because reorg needs them for its own purposes. */
+ break;
+
+ if (reg_set_p (reg, pat))
+ {
+ if (side_effects_p (pat) && !CALL_P (our_prev))
+ break;
+
+ if (GET_CODE (pat) == PARALLEL)
+ {
+ /* If we find a SET of something else, we can't
+ delete the insn. */
+
+ int i;
+
+ for (i = 0; i < XVECLEN (pat, 0); i++)
+ {
+ rtx part = XVECEXP (pat, 0, i);
+
+ if (GET_CODE (part) == SET
+ && SET_DEST (part) != reg)
+ break;
+ }
+
+ if (i == XVECLEN (pat, 0))
+ delete_computation (our_prev);
+ }
+ else if (GET_CODE (pat) == SET
+ && REG_P (SET_DEST (pat)))
+ {
+ int dest_regno = REGNO (SET_DEST (pat));
+ int dest_endregno = END_REGNO (SET_DEST (pat));
+ int regno = REGNO (reg);
+ int endregno = END_REGNO (reg);
+
+ if (dest_regno >= regno
+ && dest_endregno <= endregno)
+ delete_computation (our_prev);
+
+ /* We may have a multi-word hard register and some, but not
+ all, of the words of the register are needed in subsequent
+ insns. Write REG_UNUSED notes for those parts that were not
+ needed. */
+ else if (dest_regno <= regno
+ && dest_endregno >= endregno)
+ {
+ int i;
+
+ add_reg_note (our_prev, REG_UNUSED, reg);
+
+ for (i = dest_regno; i < dest_endregno; i++)
+ if (! find_regno_note (our_prev, REG_UNUSED, i))
+ break;
+
+ if (i == dest_endregno)
+ delete_computation (our_prev);
+ }
+ }
+
+ break;
+ }
+
+ /* If PAT references the register that dies here, it is an
+ additional use. Hence any prior SET isn't dead. However, this
+ insn becomes the new place for the REG_DEAD note. */
+ if (reg_overlap_mentioned_p (reg, pat))
+ {
+ XEXP (note, 1) = REG_NOTES (our_prev);
+ REG_NOTES (our_prev) = note;
+ break;
+ }
+ }
+}
+
+/* Delete INSN and recursively delete insns that compute values used only
+ by INSN. This uses the REG_DEAD notes computed during flow analysis.
+
+ Look at all our REG_DEAD notes. If a previous insn does nothing other
+ than set a register that dies in this insn, we can delete that insn
+ as well.
+
+ On machines with CC0, if CC0 is used in this insn, we may be able to
+ delete the insn that set it. */
+
+static void
+delete_computation (rtx insn)
+{
+ rtx note, next;
+
+#ifdef HAVE_cc0
+ if (reg_referenced_p (cc0_rtx, PATTERN (insn)))
+ {
+ rtx prev = prev_nonnote_insn (insn);
+ /* We assume that at this stage
+ CC's are always set explicitly
+ and always immediately before the jump that
+ will use them. So if the previous insn
+ exists to set the CC's, delete it
+ (unless it performs auto-increments, etc.). */
+ if (prev && NONJUMP_INSN_P (prev)
+ && sets_cc0_p (PATTERN (prev)))
+ {
+ if (sets_cc0_p (PATTERN (prev)) > 0
+ && ! side_effects_p (PATTERN (prev)))
+ delete_computation (prev);
+ else
+ /* Otherwise, show that cc0 won't be used. */
+ add_reg_note (prev, REG_UNUSED, cc0_rtx);
+ }
+ }
+#endif
+
+ for (note = REG_NOTES (insn); note; note = next)
+ {
+ next = XEXP (note, 1);
+
+ if (REG_NOTE_KIND (note) != REG_DEAD
+ /* Verify that the REG_NOTE is legitimate. */
+ || !REG_P (XEXP (note, 0)))
+ continue;
+
+ delete_prior_computation (note, insn);
+ }
+
+ delete_related_insns (insn);
+}
+
+/* If all INSN does is set the pc, delete it,
+ and delete the insn that set the condition codes for it
+ if that's what the previous thing was. */
+
+static void
+delete_jump (rtx insn)
+{
+ rtx set = single_set (insn);
+
+ if (set && GET_CODE (SET_DEST (set)) == PC)
+ delete_computation (insn);
+}
+
+static rtx
+label_before_next_insn (rtx x, rtx scan_limit)
+{
+ rtx insn = next_active_insn (x);
+ while (insn)
+ {
+ insn = PREV_INSN (insn);
+ if (insn == scan_limit || insn == NULL_RTX)
+ return NULL_RTX;
+ if (LABEL_P (insn))
+ break;
+ }
+ return insn;
+}
+
+\f