loop.c patch: do some copy propagation
Bernd Schmidt
bernds@cygnus.co.uk
Tue Nov 30 23:59:00 GMT 1999
> A few comments.
Since it seems the patch is basically OK, I've already committed the
formatting changes. This patch shouldn't affect the behaviour. I'll
send an updated patch in a separate message.
Bernd
* loop.c (load_mems): Reformat slightly.
Index: loop.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/loop.c,v
retrieving revision 1.197
diff -u -p -r1.197 loop.c
--- loop.c 1999/11/12 04:34:37 1.197
+++ loop.c 1999/11/22 13:02:06
@@ -9715,165 +9715,164 @@ load_mems (scan_start, end, loop_top, st
rtx p;
rtx label = NULL_RTX;
rtx end_label = NULL_RTX;
+ /* Nonzero if the next instruction may never be executed. */
+ int next_maybe_never = 0;
- if (loop_mems_idx > 0)
- {
- /* Nonzero if the next instruction may never be executed. */
- int next_maybe_never = 0;
+ if (loop_mems_idx == 0)
+ return;
- /* Check to see if it's possible that some instructions in the
- loop are never executed. */
- for (p = next_insn_in_loop (scan_start, scan_start, end, loop_top);
- p != NULL_RTX && !maybe_never;
- p = next_insn_in_loop (p, scan_start, end, loop_top))
+ /* Check to see if it's possible that some instructions in the
+ loop are never executed. */
+ for (p = next_insn_in_loop (scan_start, scan_start, end, loop_top);
+ p != NULL_RTX && !maybe_never;
+ p = next_insn_in_loop (p, scan_start, end, loop_top))
+ {
+ if (GET_CODE (p) == CODE_LABEL)
+ maybe_never = 1;
+ else if (GET_CODE (p) == JUMP_INSN
+ /* If we enter the loop in the middle, and scan
+ around to the beginning, don't set maybe_never
+ for that. This must be an unconditional jump,
+ otherwise the code at the top of the loop might
+ never be executed. Unconditional jumps are
+ followed a by barrier then loop end. */
+ && ! (GET_CODE (p) == JUMP_INSN
+ && JUMP_LABEL (p) == loop_top
+ && NEXT_INSN (NEXT_INSN (p)) == end
+ && simplejump_p (p)))
{
- if (GET_CODE (p) == CODE_LABEL)
- maybe_never = 1;
- else if (GET_CODE (p) == JUMP_INSN
- /* If we enter the loop in the middle, and scan
- around to the beginning, don't set maybe_never
- for that. This must be an unconditional jump,
- otherwise the code at the top of the loop might
- never be executed. Unconditional jumps are
- followed a by barrier then loop end. */
- && ! (GET_CODE (p) == JUMP_INSN
- && JUMP_LABEL (p) == loop_top
- && NEXT_INSN (NEXT_INSN (p)) == end
- && simplejump_p (p)))
- {
- if (!condjump_p (p))
- /* Something complicated. */
- maybe_never = 1;
- else
- /* If there are any more instructions in the loop, they
- might not be reached. */
- next_maybe_never = 1;
- }
- else if (next_maybe_never)
+ if (!condjump_p (p))
+ /* Something complicated. */
maybe_never = 1;
- }
+ else
+ /* If there are any more instructions in the loop, they
+ might not be reached. */
+ next_maybe_never = 1;
+ }
+ else if (next_maybe_never)
+ maybe_never = 1;
+ }
- /* Actually move the MEMs. */
- for (i = 0; i < loop_mems_idx; ++i)
+ /* Actually move the MEMs. */
+ for (i = 0; i < loop_mems_idx; ++i)
+ {
+ int written = 0;
+ rtx reg;
+ rtx mem = loop_mems[i].mem;
+ rtx mem_list_entry;
+
+ if (MEM_VOLATILE_P (mem)
+ || invariant_p (XEXP (mem, 0)) != 1)
+ /* There's no telling whether or not MEM is modified. */
+ loop_mems[i].optimize = 0;
+
+ /* Go through the MEMs written to in the loop to see if this
+ one is aliased by one of them. */
+ mem_list_entry = loop_store_mems;
+ while (mem_list_entry)
{
- int written = 0;
- rtx reg;
- rtx mem = loop_mems[i].mem;
- rtx mem_list_entry;
-
- if (MEM_VOLATILE_P (mem)
- || invariant_p (XEXP (mem, 0)) != 1)
- /* There's no telling whether or not MEM is modified. */
- loop_mems[i].optimize = 0;
-
- /* Go through the MEMs written to in the loop to see if this
- one is aliased by one of them. */
- mem_list_entry = loop_store_mems;
- while (mem_list_entry)
+ if (rtx_equal_p (mem, XEXP (mem_list_entry, 0)))
+ written = 1;
+ else if (true_dependence (XEXP (mem_list_entry, 0), VOIDmode,
+ mem, rtx_varies_p))
{
- if (rtx_equal_p (mem, XEXP (mem_list_entry, 0)))
- written = 1;
- else if (true_dependence (XEXP (mem_list_entry, 0), VOIDmode,
- mem, rtx_varies_p))
- {
- /* MEM is indeed aliased by this store. */
- loop_mems[i].optimize = 0;
- break;
- }
- mem_list_entry = XEXP (mem_list_entry, 1);
+ /* MEM is indeed aliased by this store. */
+ loop_mems[i].optimize = 0;
+ break;
}
+ mem_list_entry = XEXP (mem_list_entry, 1);
+ }
- /* If this MEM is written to, we must be sure that there
- are no reads from another MEM that aliases this one. */
- if (loop_mems[i].optimize && written)
- {
- int j;
+ /* If this MEM is written to, we must be sure that there
+ are no reads from another MEM that aliases this one. */
+ if (loop_mems[i].optimize && written)
+ {
+ int j;
- for (j = 0; j < loop_mems_idx; ++j)
+ for (j = 0; j < loop_mems_idx; ++j)
+ {
+ if (j == i)
+ continue;
+ else if (true_dependence (mem,
+ VOIDmode,
+ loop_mems[j].mem,
+ rtx_varies_p))
{
- if (j == i)
- continue;
- else if (true_dependence (mem,
- VOIDmode,
- loop_mems[j].mem,
- rtx_varies_p))
- {
- /* It's not safe to hoist loop_mems[i] out of
- the loop because writes to it might not be
- seen by reads from loop_mems[j]. */
- loop_mems[i].optimize = 0;
- break;
- }
+ /* It's not safe to hoist loop_mems[i] out of
+ the loop because writes to it might not be
+ seen by reads from loop_mems[j]. */
+ loop_mems[i].optimize = 0;
+ break;
}
}
+ }
- if (maybe_never && may_trap_p (mem))
- /* We can't access the MEM outside the loop; it might
- cause a trap that wouldn't have happened otherwise. */
- loop_mems[i].optimize = 0;
+ if (maybe_never && may_trap_p (mem))
+ /* We can't access the MEM outside the loop; it might
+ cause a trap that wouldn't have happened otherwise. */
+ loop_mems[i].optimize = 0;
- if (!loop_mems[i].optimize)
- /* We thought we were going to lift this MEM out of the
- loop, but later discovered that we could not. */
- continue;
-
- /* Allocate a pseudo for this MEM. We set REG_USERVAR_P in
- order to keep scan_loop from moving stores to this MEM
- out of the loop just because this REG is neither a
- user-variable nor used in the loop test. */
- reg = gen_reg_rtx (GET_MODE (mem));
- REG_USERVAR_P (reg) = 1;
- loop_mems[i].reg = reg;
-
- /* Now, replace all references to the MEM with the
- corresponding pesudos. */
- for (p = next_insn_in_loop (scan_start, scan_start, end, loop_top);
- p != NULL_RTX;
- p = next_insn_in_loop (p, scan_start, end, loop_top))
- {
- rtx_and_int ri;
- ri.r = p;
- ri.i = i;
- for_each_rtx (&p, replace_loop_mem, &ri);
- }
+ if (!loop_mems[i].optimize)
+ /* We thought we were going to lift this MEM out of the
+ loop, but later discovered that we could not. */
+ continue;
+
+ /* Allocate a pseudo for this MEM. We set REG_USERVAR_P in
+ order to keep scan_loop from moving stores to this MEM
+ out of the loop just because this REG is neither a
+ user-variable nor used in the loop test. */
+ reg = gen_reg_rtx (GET_MODE (mem));
+ REG_USERVAR_P (reg) = 1;
+ loop_mems[i].reg = reg;
+
+ /* Now, replace all references to the MEM with the
+ corresponding pesudos. */
+ for (p = next_insn_in_loop (scan_start, scan_start, end, loop_top);
+ p != NULL_RTX;
+ p = next_insn_in_loop (p, scan_start, end, loop_top))
+ {
+ rtx_and_int ri;
+ ri.r = p;
+ ri.i = i;
+ for_each_rtx (&p, replace_loop_mem, &ri);
+ }
- if (!apply_change_group ())
- /* We couldn't replace all occurrences of the MEM. */
- loop_mems[i].optimize = 0;
- else
- {
- rtx set;
+ if (! apply_change_group ())
+ /* We couldn't replace all occurrences of the MEM. */
+ loop_mems[i].optimize = 0;
+ else
+ {
+ rtx set;
- /* Load the memory immediately before START, which is
- the NOTE_LOOP_BEG. */
- set = gen_move_insn (reg, mem);
- emit_insn_before (set, start);
+ /* Load the memory immediately before START, which is
+ the NOTE_LOOP_BEG. */
+ set = gen_move_insn (reg, mem);
+ emit_insn_before (set, start);
- if (written)
+ if (written)
+ {
+ if (label == NULL_RTX)
{
- if (label == NULL_RTX)
- {
- /* We must compute the former
- right-after-the-end label before we insert
- the new one. */
- end_label = next_label (end);
- label = gen_label_rtx ();
- emit_label_after (label, end);
- }
-
- /* Store the memory immediately after END, which is
- the NOTE_LOOP_END. */
- set = gen_move_insn (copy_rtx (mem), reg);
- emit_insn_after (set, label);
+ /* We must compute the former
+ right-after-the-end label before we insert
+ the new one. */
+ end_label = next_label (end);
+ label = gen_label_rtx ();
+ emit_label_after (label, end);
}
- if (loop_dump_stream)
- {
- fprintf (loop_dump_stream, "Hoisted regno %d %s from ",
- REGNO (reg), (written ? "r/w" : "r/o"));
- print_rtl (loop_dump_stream, mem);
- fputc ('\n', loop_dump_stream);
- }
+ /* Store the memory immediately after END, which is
+ the NOTE_LOOP_END. */
+ set = gen_move_insn (copy_rtx (mem), reg);
+ emit_insn_after (set, label);
+ }
+
+ if (loop_dump_stream)
+ {
+ fprintf (loop_dump_stream, "Hoisted regno %d %s from ",
+ REGNO (reg), (written ? "r/w" : "r/o"));
+ print_rtl (loop_dump_stream, mem);
+ fputc ('\n', loop_dump_stream);
}
}
}
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