Tarantool development patches archive
 help / color / mirror / Atom feed
* [Tarantool-patches] [PATCH luajit] Fix HREFK forwarding vs. table.clear().
@ 2023-11-09 12:26 Sergey Kaplun via Tarantool-patches
  2023-11-10 12:49 ` Maxim Kokryashkin via Tarantool-patches
                   ` (2 more replies)
  0 siblings, 3 replies; 6+ messages in thread
From: Sergey Kaplun via Tarantool-patches @ 2023-11-09 12:26 UTC (permalink / raw)
  To: Maxim Kokryashkin, Sergey Bronnikov; +Cc: tarantool-patches

From: Mike Pall <mike>

Reported by XmiliaH.

(cherry-picked from commit d5a237eae03d2ad346f82390836371a952e9a286)

When performing HREFK (and also ALOAD, HLOAD) forwarding optimization,
the `table.clear()` function call may be performed on the table operand
from HREFK between table creation and IR, from which value is forwarded.
This call isn't taken in the account, so it may lead to too optimistic
value-forwarding from NEWREF (and also ASTORE, HSTORE), or the omitted
type guard for HREFK operation. Therefore, this leads to incorrect trace
behaviour (for example, taking a non-nil value from the cleared table).

This patch adds necessary checks for `table.clear()` calls.

Sergey Kaplun:
* added the description and the test for the problem

Part of tarantool/tarantool#9145
---

Branch: https://github.com/tarantool/luajit/tree/skaplun/lj-792-hrefk-table-clear
Tarantool PR: https://github.com/tarantool/tarantool/pull/9351
Relate issues:
* https://github.com/LuaJIT/LuaJIT/issues/792
* https://github.com/tarantool/tarantool/issues/9145

 src/lj_opt_mem.c                              |  63 +++---
 .../lj-792-hrefk-table-clear.test.lua         | 181 ++++++++++++++++++
 2 files changed, 213 insertions(+), 31 deletions(-)
 create mode 100644 test/tarantool-tests/lj-792-hrefk-table-clear.test.lua

diff --git a/src/lj_opt_mem.c b/src/lj_opt_mem.c
index a83558ac..24a490d5 100644
--- a/src/lj_opt_mem.c
+++ b/src/lj_opt_mem.c
@@ -72,6 +72,34 @@ static AliasRet aa_table(jit_State *J, IRRef ta, IRRef tb)
   return aa_escape(J, taba, tabb);
 }
 
+/* Check whether there's no aliasing table.clear. */
+static int fwd_aa_tab_clear(jit_State *J, IRRef lim, IRRef ta)
+{
+  IRRef ref = J->chain[IR_CALLS];
+  while (ref > lim) {
+    IRIns *calls = IR(ref);
+    if (calls->op2 == IRCALL_lj_tab_clear &&
+	(ta == calls->op1 || aa_table(J, ta, calls->op1) != ALIAS_NO))
+      return 0;  /* Conflict. */
+    ref = calls->prev;
+  }
+  return 1;  /* No conflict. Can safely FOLD/CSE. */
+}
+
+/* Check whether there's no aliasing NEWREF/table.clear for the left operand. */
+int LJ_FASTCALL lj_opt_fwd_tptr(jit_State *J, IRRef lim)
+{
+  IRRef ta = fins->op1;
+  IRRef ref = J->chain[IR_NEWREF];
+  while (ref > lim) {
+    IRIns *newref = IR(ref);
+    if (ta == newref->op1 || aa_table(J, ta, newref->op1) != ALIAS_NO)
+      return 0;  /* Conflict. */
+    ref = newref->prev;
+  }
+  return fwd_aa_tab_clear(J, lim, ta);
+}
+
 /* Alias analysis for array and hash access using key-based disambiguation. */
 static AliasRet aa_ahref(jit_State *J, IRIns *refa, IRIns *refb)
 {
@@ -154,7 +182,8 @@ static TRef fwd_ahload(jit_State *J, IRRef xref)
     IRIns *ir = (xr->o == IR_HREFK || xr->o == IR_AREF) ? IR(xr->op1) : xr;
     IRRef tab = ir->op1;
     ir = IR(tab);
-    if (ir->o == IR_TNEW || (ir->o == IR_TDUP && irref_isk(xr->op2))) {
+    if ((ir->o == IR_TNEW || (ir->o == IR_TDUP && irref_isk(xr->op2))) &&
+	fwd_aa_tab_clear(J, tab, tab)) {
       /* A NEWREF with a number key may end up pointing to the array part.
       ** But it's referenced from HSTORE and not found in the ASTORE chain.
       ** Or a NEWREF may rehash the table and move unrelated number keys.
@@ -275,7 +304,7 @@ TRef LJ_FASTCALL lj_opt_fwd_hrefk(jit_State *J)
   while (ref > tab) {
     IRIns *newref = IR(ref);
     if (tab == newref->op1) {
-      if (fright->op1 == newref->op2)
+      if (fright->op1 == newref->op2 && fwd_aa_tab_clear(J, ref, tab))
 	return ref;  /* Forward from NEWREF. */
       else
 	goto docse;
@@ -285,7 +314,7 @@ TRef LJ_FASTCALL lj_opt_fwd_hrefk(jit_State *J)
     ref = newref->prev;
   }
   /* No conflicting NEWREF: key location unchanged for HREFK of TDUP. */
-  if (IR(tab)->o == IR_TDUP)
+  if (IR(tab)->o == IR_TDUP && fwd_aa_tab_clear(J, tab, tab))
     fins->t.irt &= ~IRT_GUARD;  /* Drop HREFK guard. */
 docse:
   return CSEFOLD;
@@ -319,34 +348,6 @@ int LJ_FASTCALL lj_opt_fwd_href_nokey(jit_State *J)
   return 1;  /* No conflict. Can fold to niltv. */
 }
 
-/* Check whether there's no aliasing table.clear. */
-static int fwd_aa_tab_clear(jit_State *J, IRRef lim, IRRef ta)
-{
-  IRRef ref = J->chain[IR_CALLS];
-  while (ref > lim) {
-    IRIns *calls = IR(ref);
-    if (calls->op2 == IRCALL_lj_tab_clear &&
-	(ta == calls->op1 || aa_table(J, ta, calls->op1) != ALIAS_NO))
-      return 0;  /* Conflict. */
-    ref = calls->prev;
-  }
-  return 1;  /* No conflict. Can safely FOLD/CSE. */
-}
-
-/* Check whether there's no aliasing NEWREF/table.clear for the left operand. */
-int LJ_FASTCALL lj_opt_fwd_tptr(jit_State *J, IRRef lim)
-{
-  IRRef ta = fins->op1;
-  IRRef ref = J->chain[IR_NEWREF];
-  while (ref > lim) {
-    IRIns *newref = IR(ref);
-    if (ta == newref->op1 || aa_table(J, ta, newref->op1) != ALIAS_NO)
-      return 0;  /* Conflict. */
-    ref = newref->prev;
-  }
-  return fwd_aa_tab_clear(J, lim, ta);
-}
-
 /* ASTORE/HSTORE elimination. */
 TRef LJ_FASTCALL lj_opt_dse_ahstore(jit_State *J)
 {
diff --git a/test/tarantool-tests/lj-792-hrefk-table-clear.test.lua b/test/tarantool-tests/lj-792-hrefk-table-clear.test.lua
new file mode 100644
index 00000000..e662e0cc
--- /dev/null
+++ b/test/tarantool-tests/lj-792-hrefk-table-clear.test.lua
@@ -0,0 +1,181 @@
+local tap = require('tap')
+
+-- Test file to demonstrate LuaJIT incorrect optimizations across
+-- the `table.clear()` call.
+-- See also: https://github.com/LuaJIT/LuaJIT/issues/792.
+
+local test = tap.test('lj-792-hrefk-table-clear'):skipcond({
+  ['Test requires JIT enabled'] = not jit.status(),
+})
+local table_clear = require('table.clear')
+
+test:plan(7)
+
+local NITERATIONS = 4
+local MAGIC = 42
+
+local function test_aref_fwd_tnew(tab_number)
+  local field_value_after_clear
+  for i = 1, NITERATIONS do
+    -- Create a table on trace to make the optimization work.
+    -- Initialize the first field to work with the array part.
+    local tab = {i}
+    -- Use an additional table to alias the created table with the
+    -- `1` key.
+    local tab_array = {tab, {0}}
+    -- AREF to be forwarded.
+    tab[1] = MAGIC
+    table_clear(tab_array[tab_number])
+    -- It should be `nil`, since table is cleared.
+    field_value_after_clear = tab[1]
+  end
+  return field_value_after_clear
+end
+
+local function test_aref_fwd_tdup(tab_number)
+  local field_value_after_clear
+  for _ = 1, NITERATIONS do
+    -- Create a table on trace to make the optimization work.
+    local tab = {nil}
+    -- Use an additional table to alias the created table with the
+    -- `1` key.
+    local tab_array = {tab, {0}}
+    -- AREF to be forwarded.
+    tab[1] = MAGIC
+    table_clear(tab_array[tab_number])
+    -- It should be `nil`, since table is cleared.
+    field_value_after_clear = tab[1]
+  end
+  return field_value_after_clear
+end
+
+local function test_href_fwd_tnew(tab_number)
+  local field_value_after_clear
+  for _ = 1, NITERATIONS do
+    -- Create a table on trace to make the optimization work.
+    local tab = {}
+    -- Use an additional table to alias the created table with the
+    -- `8` key.
+    local tab_array = {tab, {0}}
+    -- HREF to be forwarded. Use 8 to be in the hash part.
+    tab[8] = MAGIC
+    table_clear(tab_array[tab_number])
+    -- It should be `nil`, since table is cleared.
+    field_value_after_clear = tab[8]
+  end
+  return field_value_after_clear
+end
+
+local function test_href_fwd_tdup(tab_number)
+  local field_value_after_clear
+  for _ = 1, NITERATIONS do
+    -- Create a table on trace to make the optimization work.
+    local tab = {nil}
+    -- Use an additional table to alias the created table with the
+    -- `8` key.
+    local tab_array = {tab, {0}}
+    -- HREF to be forwarded. Use 8 to be in the hash part.
+    tab[8] = MAGIC
+    table_clear(tab_array[tab_number])
+    -- It should be `nil`, since table is cleared.
+    field_value_after_clear = tab[8]
+  end
+  return field_value_after_clear
+end
+
+jit.opt.start('hotloop=1')
+
+-- First compile the trace with a clearing not-interesting table.
+test_aref_fwd_tnew(2)
+-- Now run the trace with the clearing table, from which we take
+-- AREF.
+test:is(test_aref_fwd_tnew(1), nil, 'AREF forward from TNEW')
+
+-- XXX: Reset hotcounters to avoid collisions.
+jit.opt.start('hotloop=1')
+
+-- First compile the trace with a clearing not-interesting table.
+test_aref_fwd_tdup(2)
+-- Now run the trace with the clearing table, from which we take
+-- AREF.
+test:is(test_aref_fwd_tdup(1), nil, 'AREF forward from TDUP')
+
+-- XXX: Reset hotcounters to avoid collisions.
+jit.opt.start('hotloop=1')
+
+-- First compile the trace with a clearing not-interesting table.
+test_href_fwd_tnew(2)
+-- Now run the trace with the clearing table, from which we take
+-- HREF.
+test:is(test_href_fwd_tnew(1), nil, 'HREF forward from TNEW')
+
+-- XXX: Reset hotcounters to avoid collisions.
+jit.opt.start('hotloop=1')
+
+-- First compile the trace with a clearing not-interesting table.
+test_href_fwd_tdup(2)
+-- Now run the trace with the clearing table, from which we take
+-- HREF.
+test:is(test_href_fwd_tdup(1), nil, 'HREF forward from TDUP')
+
+local function test_not_forwarded_hrefk_val_from_newref(tab_number)
+  local field_value_after_clear
+  for _ = 1, NITERATIONS do
+    -- Create a table on trace to make the optimization work.
+    local tab = {}
+    -- NEWREF to be forwarded.
+    tab.hrefk = MAGIC
+    -- Use an additional table to alias the created table with the
+    -- `hrefk` key.
+    local tab_array = {tab, {hrefk = 0}}
+    table_clear(tab_array[tab_number])
+    -- It should be `nil`, since it is cleared.
+    field_value_after_clear = tab.hrefk
+  end
+  return field_value_after_clear
+end
+
+-- XXX: Reset hotcounters to avoid collisions.
+jit.opt.start('hotloop=1')
+
+-- First compile the trace with a clearing not-interesting table.
+test_not_forwarded_hrefk_val_from_newref(2)
+-- Now run the trace with the clearing table, from which we take
+-- HREFK.
+local value_from_cleared_tab = test_not_forwarded_hrefk_val_from_newref(1)
+
+test:is(value_from_cleared_tab, nil,
+        'not forward the field value across table.clear')
+
+local function test_not_dropped_guard_on_hrefk(tab_number)
+  local tab, field_value_after_clear
+  for _ = 1, NITERATIONS do
+    -- Create a table on trace to make the optimization work.
+    tab = {hrefk = MAGIC}
+    -- Use an additional table to alias the created table with the
+    -- `hrefk` key.
+    local tab_array = {tab, {hrefk = 0}}
+    table_clear(tab_array[tab_number])
+    -- It should be `nil`, since it is cleared.
+    -- If the guard is dropped for HREFK, the value from the TDUP
+    -- table is taken instead, without the type check. This leads
+    -- to incorrect (swapped) returned values.
+    field_value_after_clear = tab.hrefk
+    tab.hrefk = MAGIC
+  end
+  return field_value_after_clear, tab.hrefk
+end
+
+-- XXX: Reset hotcounters to avoid collisions.
+jit.opt.start('hotloop=1')
+
+-- First compile the trace with clearing not interesting table.
+test_not_dropped_guard_on_hrefk(2)
+-- Now run the trace with the clearing table, from which we take
+-- HREFK.
+local field_value_after_clear, tab_hrefk = test_not_dropped_guard_on_hrefk(1)
+
+test:is(field_value_after_clear, nil, 'correct field value after table.clear')
+test:is(tab_hrefk, MAGIC, 'correct value set in the table that was cleared')
+
+test:done(true)
-- 
2.42.0


^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2024-01-10  8:57 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-11-09 12:26 [Tarantool-patches] [PATCH luajit] Fix HREFK forwarding vs. table.clear() Sergey Kaplun via Tarantool-patches
2023-11-10 12:49 ` Maxim Kokryashkin via Tarantool-patches
2023-11-13  7:37   ` Sergey Kaplun via Tarantool-patches
2023-11-15 11:46     ` Maxim Kokryashkin via Tarantool-patches
2023-11-22 15:25 ` Sergey Bronnikov via Tarantool-patches
2024-01-10  8:51 ` Igor Munkin via Tarantool-patches

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox