This adds a little mini-pass to shrink-wrapping, to eliminate a common
case that often makes shrink-wrapping unavailable. If a move insn copies
an argument registers to a call-saved register, the prologue must be
emitted before this insn. We should therefore try to delay such moves
for as long as possible.
A followup patch will add an extra cprop pass, which replaces uses of
the call-saved register with uses of the incoming argument register,
thereby allowing us to move the copies in even more cases.
Bootstrapped and tested on i686-linux. Ok?
Bernd
* function.c (prepare_shrink_wrap, bb_active_p): New function.
(thread_prologue_and_epilogue_insns): Use bb_active_p.
Call prepare_shrink_wrap, then recompute bb_active_p for the
last block.
Index: gcc/function.c
===================================================================
--- gcc/function.c (revision 179577)
+++ gcc/function.c (working copy)
@@ -5352,6 +5352,127 @@ requires_stack_frame_p (rtx insn, HARD_R
return true;
return false;
}
+
+/* Look for sets of call-saved registers in the first block of the
+ function, and move them down into successor blocks if the register
+ is used only on one path. This exposes more opportunities for
+ shrink-wrapping.
+ These kinds of sets often occur when incoming argument registers are
+ moved to call-saved registers because their values are live across
+ one or more calls during the function. */
+
+static void
+prepare_shrink_wrap (basic_block entry_block)
+{
+ rtx insn, curr;
+ FOR_BB_INSNS_SAFE (entry_block, insn, curr)
+ {
+ basic_block next_bb;
+ edge e, live_edge;
+ edge_iterator ei;
+ rtx set, scan;
+ unsigned destreg, srcreg;
+
+ if (!NONDEBUG_INSN_P (insn))
+ continue;
+ set = single_set (insn);
+ if (!set)
+ continue;
+
+ if (!REG_P (SET_SRC (set)) || !REG_P (SET_DEST (set)))
+ continue;
+ srcreg = REGNO (SET_SRC (set));
+ destreg = REGNO (SET_DEST (set));
+ if (hard_regno_nregs[srcreg][GET_MODE (SET_SRC (set))] > 1
+ || hard_regno_nregs[destreg][GET_MODE (SET_DEST (set))] > 1)
+ continue;
+
+ next_bb = entry_block;
+ scan = insn;
+
+ for (;;)
+ {
+ live_edge = NULL;
+ FOR_EACH_EDGE (e, ei, next_bb->succs)
+ {
+ if (REGNO_REG_SET_P (df_get_live_in (e->dest), destreg))
+ {
+ if (live_edge)
+ {
+ live_edge = NULL;
+ break;
+ }
+ live_edge = e;
+ }
+ }
+ if (!live_edge)
+ break;
+ /* We can sometimes encounter dead code. Don't try to move it
+ into the exit block. */
+ if (live_edge->dest == EXIT_BLOCK_PTR)
+ break;
+ if (EDGE_COUNT (live_edge->dest->preds) > 1)
+ break;
+ while (scan != BB_END (next_bb))
+ {
+ scan = NEXT_INSN (scan);
+ if (NONDEBUG_INSN_P (scan))
+ {
+ rtx link;
+ HARD_REG_SET set_regs;
+
+ CLEAR_HARD_REG_SET (set_regs);
+ note_stores (PATTERN (scan), record_hard_reg_sets,
+ &set_regs);
+ if (CALL_P (scan))
+ IOR_HARD_REG_SET (set_regs, call_used_reg_set);
+ for (link = REG_NOTES (scan); link; link = XEXP (link, 1))
+ if (REG_NOTE_KIND (link) == REG_INC)
+ record_hard_reg_sets (XEXP (link, 0), NULL, &set_regs);
+
+ if (TEST_HARD_REG_BIT (set_regs, srcreg)
+ || reg_referenced_p (SET_DEST (set),
+ PATTERN (scan)))
+ {
+ scan = NULL_RTX;
+ break;
+ }
+ if (CALL_P (scan))
+ {
+ rtx link = CALL_INSN_FUNCTION_USAGE (scan);
+ while (link)
+ {
+ rtx tmp = XEXP (link, 0);
+ if (GET_CODE (tmp) == USE
+ && reg_referenced_p (SET_DEST (set), tmp))
+ break;
+ link = XEXP (link, 1);
+ }
+ if (link)
+ {
+ scan = NULL_RTX;
+ break;
+ }
+ }
+ }
+ }
+ if (!scan)
+ break;
+ next_bb = live_edge->dest;
+ }
+
+ if (next_bb != entry_block)
+ {
+ rtx after = BB_HEAD (next_bb);
+ while (!NOTE_P (after)
+ || NOTE_KIND (after) != NOTE_INSN_BASIC_BLOCK)
+ after = NEXT_INSN (after);
+ emit_insn_after (PATTERN (insn), after);
+ delete_insn (insn);
+ }
+ }
+}
+
#endif
#ifdef HAVE_return
@@ -5400,6 +5521,23 @@ emit_return_into_block (bool simple_p, b
}
#endif
+/* Return true if BB has any active insns. */
+static bool
+bb_active_p (basic_block bb)
+{
+ rtx label;
+
+ /* Test whether there are active instructions in the last block. */
+ label = BB_END (bb);
+ while (label && !LABEL_P (label))
+ {
+ if (active_insn_p (label))
+ break;
+ label = PREV_INSN (label);
+ }
+ return BB_HEAD (bb) != label || !LABEL_P (label);
+}
+
/* Generate the prologue and epilogue RTL if the machine supports it. Thread
this into place with notes indicating where the prologue ends and where
the epilogue begins. Update the basic block information when possible.
@@ -5486,19 +5624,8 @@ thread_prologue_and_epilogue_insns (void
exit_fallthru_edge = find_fallthru_edge (EXIT_BLOCK_PTR->preds);
if (exit_fallthru_edge != NULL)
{
- rtx label;
-
last_bb = exit_fallthru_edge->src;
- /* Test whether there are active instructions in the last block. */
- label = BB_END (last_bb);
- while (label && !LABEL_P (label))
- {
- if (active_insn_p (label))
- break;
- label = PREV_INSN (label);
- }
-
- last_bb_active = BB_HEAD (last_bb) != label || !LABEL_P (label);
+ last_bb_active = bb_active_p (last_bb);
}
else
{
@@ -5607,6 +5734,12 @@ thread_prologue_and_epilogue_insns (void
note_stores (PATTERN (p_insn), record_hard_reg_sets,
&prologue_clobbered);
+ prepare_shrink_wrap (entry_edge->dest);
+
+ /* That may have inserted instructions into the last block. */
+ if (last_bb && !last_bb_active)
+ last_bb_active = bb_active_p (last_bb);
+
bitmap_initialize (&bb_antic_flags, &bitmap_default_obstack);
bitmap_initialize (&bb_on_list, &bitmap_default_obstack);
