Tarantool development patches archive
 help / color / mirror / Atom feed
* [Tarantool-patches] [PATCH luajit v6] Fix math.min()/math.max() inconsistencies.
@ 2022-12-19  9:52 Maxim Kokryashkin via Tarantool-patches
  2022-12-23 15:42 ` Sergey Kaplun via Tarantool-patches
  0 siblings, 1 reply; 2+ messages in thread
From: Maxim Kokryashkin via Tarantool-patches @ 2022-12-19  9:52 UTC (permalink / raw)
  To: tarantool-patches, sergos, skaplun

From: Mike Pall <mike>

(cherry-picked from commit 03208c8162af9cc01ca76ee1676ca79e5abe9b60)

`math.min()`/`math.max()` could produce different results.
Previously, dirty values on the Lua stack could be
treated as arguments to `math.min()`/`math.max()`.
This patch adds check for the number of arguments provided to
math.min/max, which fixes the issue.

Also it adds the corresponding test case for
the mentioned issue and does some refactoring:
1. fcc is changed for min/max functions in ARM
assembly from LO/HI (lower/upper or unordered) to LE/PL
(lower/upper, equal or unoredered).

2. Several fold optimizations for min/max were removed
or modified.

Resolves tarantool/tarantool#6163
---

>IMHO, LO -> LT (N!=V Less than or unordered) do the same thing wo
>changing the order.
>
>IINM, an ordered comparison checks if neither operand is NaN.
>Conversely, an unordered comparison checks if either operand is a NaN.
>
>So, looks like an attempt to fix inconsistent behaviour for NaNs in
>math.min/math.max on aarch64.
>
>Also, I found inconsistent behaviour on x86 (between LuaJIT|Lua):
>
>| # on upstream build
>| $ ./luajit -Ohotloop=1 -e 'local res = {} for i = 1,4 do res[i] = math.max(0/0, math.huge) end for i = 1, #res do print(res[i]) end'
>| inf
>| inf
>| inf
>| inf
>| $ lua -e 'local res = {} for i = 1,4 do res[i] = math.max(0/0, math.huge) end for i = 1, #res do print(res[i]) end'
>| -nan
>| -nan
>| -nan
>| -nan
>
>Can you please test some similar examples on aarch64/M1?
I've tested those on M1 and here are the results:
$ ./src/luajit -Ohotloop=1 -e 'local res = {} for i=1,4 do res[i]=math.max(0/0,math.huge) end for i =1, #res do print(res[i]) end'
inf
inf
inf
inf

$ lua -e 'local res = {} for i=1,4 do res[i]=math.max(0/0,math.huge) end for i =1, #res do print(res[i]) end'
nan
nan
nan
nan

>Also, AFAICS, some optimizations are the reason of inconsistent
>behaviour for JIT-ed code (not the fold in this commit).
>| # on our fork
>| ./luajit -O0 -Ohotloop=1 -e 'local res = {} for i = 1,4 do res[i] = math.max(0/0, math.huge) end for i = 1, #res do print(res[i]) end'
>| inf
>| inf
>| inf
>| inf
>| # on our fork
>| ./luajit -Ohotloop=1 -e 'local res = {} for i = 1,4 do res[i] = math.max(0/0, math.huge) end for i = 1, #res do print(res[i]) end'
>| inf
>| inf
>| inf
>| nan
>
>BTW this commit doesn't fix the problem. Can you please bisect the
>commit to backport?
Works perfectly fine on our fork after this patch.

>> diff --git a/src/lj_opt_fold.c b/src/lj_opt_fold.c
>> index 276dc040..07a52a4d 100644
>> --- a/src/lj_opt_fold.c
>> +++ b/src/lj_opt_fold.c
>> @@ -1774,8 +1774,6 @@ LJFOLDF(reassoc_intarith_k64)
>> #endif
>> }
>>
>> -LJFOLD(MIN MIN any)
>> -LJFOLD(MAX MAX any)
>> LJFOLD(BAND BAND any)
>> LJFOLD(BOR BOR any)
>> LJFOLDF(reassoc_dup)
>> @@ -1785,6 +1783,15 @@ LJFOLDF(reassoc_dup)
>> return NEXTFOLD;
>> }
>>
>> +LJFOLD(MIN MIN any)
>> +LJFOLD(MAX MAX any)
>> +LJFOLDF(reassoc_dup_minmax)
>> +{
>> + if (fins->op2 == fleft->op2)
>> + return LEFTFOLD; /* (a o b) o b ==> a o b */
>> + return NEXTFOLD;
>> +}
>> +
>
>Do you know why the opt `(a o b) o a ==> a o b;` is ommited now?
>Are there any examples of incorrect behaviour? I suggest to check NaN
>behaviour in this case.
Added the test case for that one, but I failed to find any for the
other.

I've done test runs on all of the combinations of `{1, -1, 0, -0, 0/0,
-math.huge, math.huge}` for all of the optimizations.

I'll be glad to add another test case if you can think of any.

 src/lj_asm_arm.h                              |  6 +--
 src/lj_asm_arm64.h                            |  6 +--
 src/lj_opt_fold.c                             | 53 +++++++------------
 src/lj_vmmath.c                               |  4 +-
 src/vm_arm.dasc                               |  4 +-
 src/vm_arm64.dasc                             |  4 +-
 src/vm_x64.dasc                               |  2 +-
 src/vm_x86.dasc                               |  2 +-
 test/tarantool-tests/gh-6163-min-max.test.lua | 48 +++++++++++++++++
 9 files changed, 81 insertions(+), 48 deletions(-)
 create mode 100644 test/tarantool-tests/gh-6163-min-max.test.lua

diff --git a/src/lj_asm_arm.h b/src/lj_asm_arm.h
index 8af19eb9..6ae6e2f2 100644
--- a/src/lj_asm_arm.h
+++ b/src/lj_asm_arm.h
@@ -1663,8 +1663,8 @@ static void asm_min_max(ASMState *as, IRIns *ir, int cc, int fcc)
     asm_intmin_max(as, ir, cc);
 }
 
-#define asm_min(as, ir)		asm_min_max(as, ir, CC_GT, CC_HI)
-#define asm_max(as, ir)		asm_min_max(as, ir, CC_LT, CC_LO)
+#define asm_min(as, ir)		asm_min_max(as, ir, CC_GT, CC_PL)
+#define asm_max(as, ir)		asm_min_max(as, ir, CC_LT, CC_LE)
 
 /* -- Comparisons --------------------------------------------------------- */
 
@@ -1856,7 +1856,7 @@ static void asm_hiop(ASMState *as, IRIns *ir)
   } else if ((ir-1)->o == IR_MIN || (ir-1)->o == IR_MAX) {
     as->curins--;  /* Always skip the loword min/max. */
     if (uselo || usehi)
-      asm_sfpmin_max(as, ir-1, (ir-1)->o == IR_MIN ? CC_HI : CC_LO);
+      asm_sfpmin_max(as, ir-1, (ir-1)->o == IR_MIN ? CC_PL : CC_LE);
     return;
 #elif LJ_HASFFI
   } else if ((ir-1)->o == IR_CONV) {
diff --git a/src/lj_asm_arm64.h b/src/lj_asm_arm64.h
index 4aeb51f3..fe197700 100644
--- a/src/lj_asm_arm64.h
+++ b/src/lj_asm_arm64.h
@@ -1592,7 +1592,7 @@ static void asm_fpmin_max(ASMState *as, IRIns *ir, A64CC fcc)
   Reg dest = (ra_dest(as, ir, RSET_FPR) & 31);
   Reg right, left = ra_alloc2(as, ir, RSET_FPR);
   right = ((left >> 8) & 31); left &= 31;
-  emit_dnm(as, A64I_FCSELd | A64F_CC(fcc), dest, left, right);
+  emit_dnm(as, A64I_FCSELd | A64F_CC(fcc), dest, right, left);
   emit_nm(as, A64I_FCMPd, left, right);
 }
 
@@ -1604,8 +1604,8 @@ static void asm_min_max(ASMState *as, IRIns *ir, A64CC cc, A64CC fcc)
     asm_intmin_max(as, ir, cc);
 }
 
-#define asm_max(as, ir)		asm_min_max(as, ir, CC_GT, CC_HI)
-#define asm_min(as, ir)		asm_min_max(as, ir, CC_LT, CC_LO)
+#define asm_min(as, ir)		asm_min_max(as, ir, CC_LT, CC_PL)
+#define asm_max(as, ir)		asm_min_max(as, ir, CC_GT, CC_LE)
 
 /* -- Comparisons --------------------------------------------------------- */
 
diff --git a/src/lj_opt_fold.c b/src/lj_opt_fold.c
index 49f74996..27e489af 100644
--- a/src/lj_opt_fold.c
+++ b/src/lj_opt_fold.c
@@ -1797,8 +1797,6 @@ LJFOLDF(reassoc_intarith_k64)
 #endif
 }
 
-LJFOLD(MIN MIN any)
-LJFOLD(MAX MAX any)
 LJFOLD(BAND BAND any)
 LJFOLD(BOR BOR any)
 LJFOLDF(reassoc_dup)
@@ -1808,6 +1806,15 @@ LJFOLDF(reassoc_dup)
   return NEXTFOLD;
 }
 
+LJFOLD(MIN MIN any)
+LJFOLD(MAX MAX any)
+LJFOLDF(reassoc_dup_minmax)
+{
+  if (fins->op2 == fleft->op2)
+    return LEFTFOLD;  /* (a o b) o b ==> a o b */
+  return NEXTFOLD;
+}
+
 LJFOLD(BXOR BXOR any)
 LJFOLDF(reassoc_bxor)
 {
@@ -1846,23 +1853,12 @@ LJFOLDF(reassoc_shift)
   return NEXTFOLD;
 }
 
-LJFOLD(MIN MIN KNUM)
-LJFOLD(MAX MAX KNUM)
 LJFOLD(MIN MIN KINT)
 LJFOLD(MAX MAX KINT)
 LJFOLDF(reassoc_minmax_k)
 {
   IRIns *irk = IR(fleft->op2);
-  if (irk->o == IR_KNUM) {
-    lua_Number a = ir_knum(irk)->n;
-    lua_Number y = lj_vm_foldarith(a, knumright, fins->o - IR_ADD);
-    if (a == y)  /* (x o k1) o k2 ==> x o k1, if (k1 o k2) == k1. */
-      return LEFTFOLD;
-    PHIBARRIER(fleft);
-    fins->op1 = fleft->op1;
-    fins->op2 = (IRRef1)lj_ir_knum(J, y);
-    return RETRYFOLD;  /* (x o k1) o k2 ==> x o (k1 o k2) */
-  } else if (irk->o == IR_KINT) {
+  if (irk->o == IR_KINT) {
     int32_t a = irk->i;
     int32_t y = kfold_intop(a, fright->i, fins->o);
     if (a == y)  /* (x o k1) o k2 ==> x o k1, if (k1 o k2) == k1. */
@@ -1875,24 +1871,6 @@ LJFOLDF(reassoc_minmax_k)
   return NEXTFOLD;
 }
 
-LJFOLD(MIN MAX any)
-LJFOLD(MAX MIN any)
-LJFOLDF(reassoc_minmax_left)
-{
-  if (fins->op2 == fleft->op1 || fins->op2 == fleft->op2)
-    return RIGHTFOLD;  /* (b o1 a) o2 b ==> b; (a o1 b) o2 b ==> b */
-  return NEXTFOLD;
-}
-
-LJFOLD(MIN any MAX)
-LJFOLD(MAX any MIN)
-LJFOLDF(reassoc_minmax_right)
-{
-  if (fins->op1 == fright->op1 || fins->op1 == fright->op2)
-    return LEFTFOLD;  /* a o2 (a o1 b) ==> a; a o2 (b o1 a) ==> a */
-  return NEXTFOLD;
-}
-
 /* -- Array bounds check elimination -------------------------------------- */
 
 /* Eliminate ABC across PHIs to handle t[i-1] forwarding case.
@@ -2018,8 +1996,6 @@ LJFOLDF(comm_comp)
 
 LJFOLD(BAND any any)
 LJFOLD(BOR any any)
-LJFOLD(MIN any any)
-LJFOLD(MAX any any)
 LJFOLDF(comm_dup)
 {
   if (fins->op1 == fins->op2)  /* x o x ==> x */
@@ -2027,6 +2003,15 @@ LJFOLDF(comm_dup)
   return fold_comm_swap(J);
 }
 
+LJFOLD(MIN any any)
+LJFOLD(MAX any any)
+LJFOLDF(comm_dup_minmax)
+{
+  if (fins->op1 == fins->op2)  /* x o x ==> x */
+    return LEFTFOLD;
+  return NEXTFOLD;
+}
+
 LJFOLD(BXOR any any)
 LJFOLDF(comm_bxor)
 {
diff --git a/src/lj_vmmath.c b/src/lj_vmmath.c
index c04459bd..ae4e0f15 100644
--- a/src/lj_vmmath.c
+++ b/src/lj_vmmath.c
@@ -49,8 +49,8 @@ double lj_vm_foldarith(double x, double y, int op)
   case IR_ABS - IR_ADD: return fabs(x); break;
 #if LJ_HASJIT
   case IR_LDEXP - IR_ADD: return ldexp(x, (int)y); break;
-  case IR_MIN - IR_ADD: return x > y ? y : x; break;
-  case IR_MAX - IR_ADD: return x < y ? y : x; break;
+  case IR_MIN - IR_ADD: return x < y ? x : y; break;
+  case IR_MAX - IR_ADD: return x > y ? x : y; break;
 #endif
   default: return x;
   }
diff --git a/src/vm_arm.dasc b/src/vm_arm.dasc
index a29292f1..89faa03e 100644
--- a/src/vm_arm.dasc
+++ b/src/vm_arm.dasc
@@ -1718,8 +1718,8 @@ static void build_subroutines(BuildCtx *ctx)
   |.endif
   |.endmacro
   |
-  |  math_minmax math_min, gt, hi
-  |  math_minmax math_max, lt, lo
+  |  math_minmax math_min, gt, pl
+  |  math_minmax math_max, lt, le
   |
   |//-- String library -----------------------------------------------------
   |
diff --git a/src/vm_arm64.dasc b/src/vm_arm64.dasc
index f517a808..2c1bb4f8 100644
--- a/src/vm_arm64.dasc
+++ b/src/vm_arm64.dasc
@@ -1494,8 +1494,8 @@ static void build_subroutines(BuildCtx *ctx)
   |  b <6
   |.endmacro
   |
-  |  math_minmax math_min, gt, hi
-  |  math_minmax math_max, lt, lo
+  |  math_minmax math_min, gt, pl
+  |  math_minmax math_max, lt, le
   |
   |//-- String library -----------------------------------------------------
   |
diff --git a/src/vm_x64.dasc b/src/vm_x64.dasc
index 59f117ba..faeb5181 100644
--- a/src/vm_x64.dasc
+++ b/src/vm_x64.dasc
@@ -1896,7 +1896,7 @@ static void build_subroutines(BuildCtx *ctx)
   |  jmp ->fff_res
   |
   |.macro math_minmax, name, cmovop, sseop
-  |  .ffunc name
+  |  .ffunc_1 name
   |  mov RAd, 2
   |.if DUALNUM
   |  mov RB, [BASE]
diff --git a/src/vm_x86.dasc b/src/vm_x86.dasc
index f7ffe5d2..1c995d16 100644
--- a/src/vm_x86.dasc
+++ b/src/vm_x86.dasc
@@ -2321,7 +2321,7 @@ static void build_subroutines(BuildCtx *ctx)
   |  xorps xmm4, xmm4; jmp <1			// Return +-Inf and +-0.
   |
   |.macro math_minmax, name, cmovop, sseop
-  |  .ffunc name
+  |  .ffunc_1 name
   |  mov RA, 2
   |  cmp dword [BASE+4], LJ_TISNUM
   |.if DUALNUM
diff --git a/test/tarantool-tests/gh-6163-min-max.test.lua b/test/tarantool-tests/gh-6163-min-max.test.lua
new file mode 100644
index 00000000..1da8a259
--- /dev/null
+++ b/test/tarantool-tests/gh-6163-min-max.test.lua
@@ -0,0 +1,48 @@
+local tap = require('tap')
+local test = tap.test('gh-6163-jit-min-max')
+test:plan(3)
+--
+-- gh-6163: math.min/math.max inconsistencies.
+--
+
+local function is_consistent(res)
+  for i = 1, #res - 1 do
+    if res[i] ~= res[i + 1] then
+      return false
+    end
+  end
+  return true
+end
+
+-- This function creates dirty values on the Lua stack.
+-- The latter of them is going to be treated as an
+-- argument by the `math.min/math.max`.
+-- The first two of them are going to be overwritten
+-- by the math function itself.
+local function filler()
+  return 1, 1, 1
+end
+
+-- Success with no args.
+filler()
+local r, _ = pcall(function() math.min() end)
+test:ok(false == r, 'math.min fails with no args')
+
+filler()
+r, _ = pcall(function() math.max() end)
+test:ok(false == r, 'math.max fails with no args')
+
+-- Incorrect fold optimization.
+jit.off()
+jit.flush()
+jit.opt.start('hotloop=1')
+jit.on()
+
+local res = {}
+for i = 1, 4 do
+  res[i] = math.min(math.min(0/0, math.huge), math.huge)
+end
+
+test:ok(is_consistent(res), '(a o b) o a -> a o b')
+
+os.exit(test:check() and 0 or 1)
-- 
2.38.1


^ permalink raw reply	[flat|nested] 2+ messages in thread

end of thread, other threads:[~2022-12-23 15:46 UTC | newest]

Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-12-19  9:52 [Tarantool-patches] [PATCH luajit v6] Fix math.min()/math.max() inconsistencies Maxim Kokryashkin via Tarantool-patches
2022-12-23 15:42 ` Sergey Kaplun 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