https://gcc.gnu.org/g:f495eae10735f687366a59884a25561de823daff
commit f495eae10735f687366a59884a25561de823daff
Author: Ondřej Machota <ondrejmach...@gmail.com>
Date: Tue Apr 15 09:21:56 2025 +0200
rtl-ssa-dce: remove useless conditions and fix dead debug insns
Diff:
---
gcc/dce.cc | 87 ++++++++++++++++++++++++++++++++++----------------------------
1 file changed, 48 insertions(+), 39 deletions(-)
diff --git a/gcc/dce.cc b/gcc/dce.cc
index 40b4cd991151..630906fb1ec6 100644
--- a/gcc/dce.cc
+++ b/gcc/dce.cc
@@ -123,6 +123,8 @@ can_delete_call (rtx_insn *insn)
return true;
}
+static bool inside_ud = false;
+
/* Return true if INSN is a normal instruction that can be deleted by
the DCE pass. */
@@ -578,8 +580,6 @@ reset_unmarked_insns_debug_uses (void)
}
/* Delete every instruction that hasn't been marked. */
-static bool inside_ud = false;
-
static void
delete_unmarked_insns (void)
{
@@ -819,7 +819,6 @@ fini_dce (bool fast)
static unsigned int
rest_of_handle_ud_dce (void)
{
- inside_ud = true;
rtx_insn *insn;
init_dce (false);
@@ -833,6 +832,7 @@ rest_of_handle_ud_dce (void)
}
worklist.release ();
+ inside_ud = true;
if (MAY_HAVE_DEBUG_BIND_INSNS)
reset_unmarked_insns_debug_uses ();
@@ -1381,9 +1381,8 @@ bool is_rtx_insn_prelive(rtx_insn *insn) {
gcc_assert(GET_CODE(insn) == INSN);
/* Don't delete insns that may throw if we cannot do so. */
- if (!(cfun->can_delete_dead_exceptions && can_alter_cfg)
- && !insn_nothrow_p (insn))
- return true;
+ if (!cfun->can_delete_dead_exceptions && !insn_nothrow_p (insn))
+ return true;
/* Callee-save restores are needed. */
if (RTX_FRAME_RELATED_P (insn) && crtl->shrink_wrapped_separate
@@ -1410,8 +1409,8 @@ bool is_rtx_insn_prelive(rtx_insn *insn) {
bool is_prelive(insn_info *insn)
{
- /* Phi insns are never prelive, bb head and end contain artificial uses that
- we need to mark as prelive */
+ /* Phi insns and debug insns are never prelive, bb head and end contain
+ artificial uses that we need to mark as prelive */
if (insn->is_bb_head() || insn->is_bb_end())
return true;
@@ -1468,6 +1467,9 @@ rtl_ssa_dce_mark_prelive_insn(insn_info *insn,
auto_vec<set_info *> &worklist,
static auto_vec<set_info *>
rtl_ssa_dce_mark_prelive(std::unordered_set<insn_info *> &marked)
{
+ if (dump_file)
+ fprintf(dump_file, "DCE: prelive phase\n");
+
auto_vec<set_info *> worklist;
for (insn_info * insn : crtl->ssa->all_insns()) {
if (is_prelive(insn))
@@ -1478,12 +1480,13 @@ rtl_ssa_dce_mark_prelive(std::unordered_set<insn_info
*> &marked)
}
static std::unordered_set<insn_info *>
-rtl_ssa_dce_mark()
+rtl_ssa_dce_mark(std::unordered_set<phi_info *> &marked_phis)
{
- std::unordered_set<insn_info *> marked{};
/* Phi insn might have more that one phi node:
gcc/gcc/testsuite/gcc.c-torture/execute/20000224-1.c */
- std::unordered_set<phi_info *> marked_phi_nodes{};
+ std::unordered_set<insn_info *> marked{};
auto worklist = rtl_ssa_dce_mark_prelive(marked);
+ if (dump_file)
+ fprintf(dump_file, "DCE: marking phase\n");
while (!worklist.is_empty()) {
set_info* set = worklist.pop();
@@ -1505,10 +1508,10 @@ rtl_ssa_dce_mark()
might be used. */
phi_info* pi = as_a<phi_info *> (set);
auto pi_uid = pi->uid();
- if (marked_phi_nodes.count(pi) > 0)
+ if (marked_phis.count(pi) > 0)
continue;
- marked_phi_nodes.emplace(pi);
+ marked_phis.emplace(pi);
uses = pi->inputs();
}
@@ -1527,37 +1530,43 @@ rtl_ssa_dce_mark()
return marked;
}
+// Iterate over non-debug instructions in RPO and remove all aren't marked.
static void
rtl_ssa_dce_sweep(std::unordered_set<insn_info *> marked)
{
- /* We can get the number of items in the `marked` set and create an array
- of changes with appropriate size */
+ if (dump_file)
+ fprintf(dump_file, "DCE: Sweep phase\n");
+
auto_vec<insn_change> to_delete;
- for (insn_info * insn : crtl->ssa->all_insns()) {
- /* Artificial and marked insns cannot be deleted.
- There is a slight problem with phis, because we might want to delete
- some phi nodes from phi insn. */
- if (insn->is_artificial() || insn->is_debug_insn() || marked.count(insn) >
0)
+ for (insn_info * insn : crtl->ssa->nondebug_insns()) {
+ // Artificial or marked insns cannot be deleted.
+ if (insn->is_artificial() || marked.count(insn) > 0)
continue;
- auto change = insn_change::delete_insn(insn);
- to_delete.safe_push(change);
if (dump_file)
- fprintf(dump_file, "Sweeping insn %d\n", insn->uid());
- /* crtl->ssa->change_insn(change); */
+ fprintf(dump_file, "Sweeping insn: %d\n", insn->uid());
+
+ auto change = insn_change::delete_insn(insn);
+ to_delete.safe_push(std::move(change));
+
+ // If we use following way with reverse_nondebug_insns, not all insns seem
+ // to be deleted...
+ // crtl->ssa->change_insn(change);
}
- auto attempt = crtl->ssa->new_change_attempt ();
auto_vec<insn_change*> changes(to_delete.length());
for (size_t i = 0; i != to_delete.length(); ++i) {
changes.safe_push(&to_delete[i]);
}
gcc_assert (crtl->ssa->verify_insn_changes(changes));
- /* segfault: gcc.c-torture/execute/20000224-1.c */
crtl->ssa->change_insns(changes);
+
+ if (dump_file)
+ fprintf(dump_file, "DCE: finish sweep phase\n");
}
+// Clear debug_insn uses and set gen_rtx_UNKNOWN_VAR_LOC
static void reset_debug_insn_uses(insn_info * insn) {
gcc_assert(insn->is_debug_insn());
@@ -1570,15 +1579,19 @@ static void reset_debug_insn_uses(insn_info * insn) {
crtl->ssa->change_insn (change);
}
-// WIP
+// Iterate over all debug_insns and reset those for which at least one of the
+// uses isn't marked.
static void
-rtl_ssa_dce_reset_dead_debug(std::unordered_set<insn_info *> &marked) {
+rtl_ssa_dce_reset_dead_debug(std::unordered_set<insn_info *> &marked,
std::unordered_set<phi_info *> &marked_phis) {
for (insn_info *insn : crtl->ssa->all_insns()) {
if (!insn->is_debug_insn())
continue;
+ // TODO : use iterate_safely?
for (use_info * use: insn->uses()) {
- if (marked.count(use->def()->insn()) == 0) {
+ insn_info *parent_insn = use->def()->insn();
+ if ((parent_insn->is_phi() && marked_phis.count(as_a<phi_info
*>(use->def())) == 0)
+ || (!parent_insn->is_phi() && marked.count(parent_insn) == 0)) {
reset_debug_insn_uses(insn);
break;
}
@@ -1610,10 +1623,14 @@ rtl_ssa_dce()
{
rtl_ssa_dce_init();
// debug(crtl->ssa);
- std::unordered_set<insn_info *> marked = rtl_ssa_dce_mark();
+ if (dump_file)
+ dump(dump_file, crtl->ssa);
+ std::unordered_set<phi_info *> marked_phis;
+ std::unordered_set<insn_info *> marked = rtl_ssa_dce_mark(marked_phis);
if (MAY_HAVE_DEBUG_BIND_INSNS)
- rtl_ssa_dce_reset_dead_debug(marked);
+ rtl_ssa_dce_reset_dead_debug(marked, marked_phis);
rtl_ssa_dce_sweep(marked);
+
// std::cerr << "\033[31m" << "SSA debug start" << "\033[0m" << "\n";
// debug (crtl->ssa);
// for (insn_info * insn : crtl->ssa->all_insns()) {
@@ -1624,14 +1641,6 @@ rtl_ssa_dce()
// std::cerr << "\033[31m" << "SSA debug end" << "\033[0m" << "\n";
rtl_ssa_dce_done();
- /* We need to perform some kind of reset_unmarked_insns_debug_uses
- to be able to reproduce ud_dce - now only 4 tests are falling
- because of debug_insn being dependent on parallel with set flags
- - gcc.c-torture/execute/20051215-1.c
- - gcc.c-torture/execute/20100805-1.c
- - gcc.c-torture/execute/pr39339.c
- - gcc.c-torture/execute/pr47925.c */
-
/*
if (delete_trivially_dead_insns(get_insns (), max_reg_num ())) {
std::cerr << "\033[31m" << "rtl_ssa_dce did not delete everything :(" <<
"\033[0m" << "\n";
