Elide Decref codegen for known-immortal objects

Summary:
The JIT already has infrastructure to skip Incref/Decref for objects known to be immortal at compile time, but outputType() returned types with unknown mortality for several operations that provably produce immortal singletons (True, False, None). This caused unnecessary Decref sequences (7-11 instructions each) to be emitted.

Change outputType() to return TImmortalBool for Compare<In/NotIn>, UnaryOp<Not>, FloatCompare, LongCompare, UnicodeCompare, and PrimitiveBoxBool. Return TImmortalNoneType for ListExtend and
TOptImmortalNoneType for InitialYield.

These are safe because the JIT runtime helpers (JITRT_SequenceContains, JITRT_UnaryNot, etc.) all explicitly return Py_True/Py_False/Py_None.

The downstream refcount insertion pass automatically treats
ImmortalBool/ImmortalNoneType as uncounted, eliding all
Incref/Decref operations.

Reviewed By: DinoV

Differential Revision: D103079581

fbshipit-source-id: 5752552c489fca0af963e195bd68712addcacb5f

Author: kddnewton

cinderx/Jit/hir/pass.cpp

@@ -303,7 +303,7 @@ Type outputType(
     case Opcode::kGetTuple:
       return TTupleExact;
     case Opcode::kInitialYield:
-      return TOptNoneType;
+      return TOptImmortalNoneType;
     case Opcode::kLoadArg: {
       auto& loadarg = static_cast<const LoadArg&>(instr);
       return loadarg.type();
@@ -366,7 +366,7 @@ Type outputType(
     // we should get rid of this extra layer and deal with the int return value
     // directly.
     case Opcode::kListExtend:
-      return TNoneType;
+      return TImmortalNoneType;
 
     case Opcode::kListAppend:
     case Opcode::kMergeSetUnpack:

cinderx/RuntimeTests/hir_tests/all_passes_test.txt

@@ -685,6 +685,149 @@ fun jittestmodule:test {
   }
 }
 --- Test Name ---
+CompareInBranchElidesDecref
+--- Input ---
+def test(x, y):
+    if x in y:
+        return x
+    return y
+--- Expected 3.12 ---
+fun jittestmodule:test {
+  bb 0 {
+    v7:Object = LoadArg<0; "x">
+    v8:Object = LoadArg<1; "y">
+    LoadFrame
+    UpdatePrevInstr<idx:0 line_no:1: no parent>
+    v10:CInt32 = LoadEvalBreaker
+    CondBranch<4, 3> v10
+  }
+
+  bb 4 (preds 0) {
+    v11:CInt32 = RunPeriodicTasks {
+      LiveValues<2> b:v7 b:v8
+      FrameState {
+        CurInstrOffset 0
+        Locals<2> v7 v8
+      }
+    }
+    Branch<3>
+  }
+
+  bb 3 (preds 0, 4) {
+    v14:ImmortalBool = Compare<In> v7 v8 {
+      LiveValues<2> b:v7 b:v8
+      FrameState {
+        CurInstrOffset 6
+        Locals<2> v7 v8
+      }
+    }
+    v16:ImmortalBool[True] = LoadConst<ImmortalBool[True]>
+    v17:CBool = PrimitiveCompare<Equal> v14 v16
+    CondBranch<1, 2> v17
+  }
+
+  bb 1 (preds 3) {
+    Incref v7
+    Return v7
+  }
+
+  bb 2 (preds 3) {
+    Incref v8
+    Return v8
+  }
+}
+--- Expected 3.14 ---
+fun jittestmodule:test {
+  bb 0 {
+    v8:Object = LoadArg<0; "x">
+    v9:Object = LoadArg<1; "y">
+    LoadFrame
+    UpdatePrevInstr<idx:0 line_no:1: no parent>
+    v11:CInt64 = LoadEvalBreaker
+    CondBranch<4, 3> v11
+  }
+
+  bb 4 (preds 0) {
+    v12:CInt32 = RunPeriodicTasks {
+      LiveValues<2> b:v8 b:v9
+      FrameState {
+        CurInstrOffset 0
+        Locals<2> v8 v9
+      }
+    }
+    Branch<3>
+  }
+
+  bb 3 (preds 0, 4) {
+    v15:ImmortalBool = Compare<In> v8 v9 {
+      LiveValues<2> b:v8 b:v9
+      FrameState {
+        CurInstrOffset 4
+        Locals<2> v8 v9
+      }
+    }
+    v16:ImmortalBool[True] = LoadConst<ImmortalBool[True]>
+    v17:CBool = PrimitiveCompare<Equal> v15 v16
+    CondBranch<1, 2> v17
+  }
+
+  bb 1 (preds 3) {
+    Incref v8
+    Return v8
+  }
+
+  bb 2 (preds 3) {
+    Incref v9
+    Return v9
+  }
+}
+--- Expected 3.15 ---
+fun jittestmodule:test {
+  bb 0 {
+    v8:Object = LoadArg<0; "x">
+    v9:Object = LoadArg<1; "y">
+    LoadFrame
+    v11:CInt64 = LoadEvalBreaker
+    CondBranch<4, 3> v11
+  }
+
+  bb 4 (preds 0) {
+    UpdatePrevInstr<idx:0 line_no:1: no parent>
+    v12:CInt32 = RunPeriodicTasks {
+      LiveValues<2> b:v8 b:v9
+      FrameState {
+        CurInstrOffset 0
+        Locals<2> v8 v9
+      }
+    }
+    Branch<3>
+  }
+
+  bb 3 (preds 0, 4) {
+    UpdatePrevInstr<idx:3 line_no:2: no parent>
+    v15:ImmortalBool = Compare<In> v8 v9 {
+      LiveValues<2> b:v8 b:v9
+      FrameState {
+        CurInstrOffset 6
+        Locals<2> v8 v9
+      }
+    }
+    v16:ImmortalBool[True] = LoadConst<ImmortalBool[True]>
+    v17:CBool = PrimitiveCompare<Equal> v15 v16
+    CondBranch<1, 2> v17
+  }
+
+  bb 1 (preds 3) {
+    Incref v8
+    Return v8
+  }
+
+  bb 2 (preds 3) {
+    Incref v9
+    Return v9
+  }
+}
+--- Test Name ---
 CompareNotInReturnsBool
 --- Input ---
 def test(x, y):
@@ -966,7 +1109,7 @@ fun jittestmodule:test {
   bb 0 {
     LoadFrame
     v16:Nullptr = LoadConst<Nullptr>
-    v17:OptNoneType = InitialYield {
+    v17:OptImmortalNoneType = InitialYield {
       LiveValues<1> unc:v16
       FrameState {
         CurInstrOffset 0
@@ -1073,7 +1216,7 @@ fun jittestmodule:test {
   bb 0 {
     LoadFrame
     v16:Nullptr = LoadConst<Nullptr>
-    v17:OptNoneType = InitialYield {
+    v17:OptImmortalNoneType = InitialYield {
       LiveValues<1> unc:v16
       FrameState {
         CurInstrOffset 2
@@ -1181,7 +1324,7 @@ fun jittestmodule:test {
     LoadFrame
     v16:Nullptr = LoadConst<Nullptr>
     UpdatePrevInstr<idx:1 line_no:1: no parent>
-    v17:OptNoneType = InitialYield {
+    v17:OptImmortalNoneType = InitialYield {
       LiveValues<1> unc:v16
       FrameState {
         CurInstrOffset 2
@@ -1730,4 +1873,143 @@ fun jittestmodule:test {
     Return v22
   }
 }
+--- Test Name ---
+ListExtendElidesNoneDecref
+--- Input ---
+def test(x, y):
+    result = [*x]
+    return y
+--- Expected 3.12 ---
+fun jittestmodule:test {
+  bb 0 {
+    v8:Object = LoadArg<0; "x">
+    v9:Object = LoadArg<1; "y">
+    LoadFrame
+    v11:Nullptr = LoadConst<Nullptr>
+    UpdatePrevInstr<idx:0 line_no:1: no parent>
+    v12:CInt32 = LoadEvalBreaker
+    CondBranch<2, 1> v12
+  }
+
+  bb 2 (preds 0) {
+    v13:CInt32 = RunPeriodicTasks {
+      LiveValues<3> b:v8 b:v9 unc:v11
+      FrameState {
+        CurInstrOffset 0
+        Locals<3> v8 v9 v11
+      }
+    }
+    Branch<1>
+  }
+
+  bb 1 (preds 0, 2) {
+    v17:MortalListExact = MakeList<0> {
+      LiveValues<3> b:v8 b:v9 unc:v11
+      FrameState {
+        CurInstrOffset 2
+        Locals<3> v8 v9 v11
+      }
+    }
+    v18:ImmortalNoneType = ListExtend v17 v8 {
+      LiveValues<4> b:v8 b:v9 unc:v11 o:v17
+      FrameState {
+        CurInstrOffset 6
+        Locals<3> v8 v9 v11
+        Stack<1> v17
+      }
+    }
+    Decref v17
+    Incref v9
+    Return v9
+  }
+}
+--- Expected 3.14 ---
+fun jittestmodule:test {
+  bb 0 {
+    v8:Object = LoadArg<0; "x">
+    v9:Object = LoadArg<1; "y">
+    LoadFrame
+    v11:Nullptr = LoadConst<Nullptr>
+    UpdatePrevInstr<idx:0 line_no:1: no parent>
+    v12:CInt64 = LoadEvalBreaker
+    CondBranch<2, 1> v12
+  }
+
+  bb 2 (preds 0) {
+    v13:CInt32 = RunPeriodicTasks {
+      LiveValues<3> b:v8 b:v9 unc:v11
+      FrameState {
+        CurInstrOffset 0
+        Locals<3> v8 v9 v11
+      }
+    }
+    Branch<1>
+  }
+
+  bb 1 (preds 0, 2) {
+    v17:MortalListExact = MakeList<0> {
+      LiveValues<3> b:v8 b:v9 unc:v11
+      FrameState {
+        CurInstrOffset 2
+        Locals<3> v8 v9 v11
+      }
+    }
+    v18:ImmortalNoneType = ListExtend v17 v8 {
+      LiveValues<4> b:v8 b:v9 unc:v11 o:v17
+      FrameState {
+        CurInstrOffset 6
+        Locals<3> v8 v9 v11
+        Stack<1> v17
+      }
+    }
+    Decref v17
+    Incref v9
+    Return v9
+  }
+}
+--- Expected 3.15 ---
+fun jittestmodule:test {
+  bb 0 {
+    v8:Object = LoadArg<0; "x">
+    v9:Object = LoadArg<1; "y">
+    LoadFrame
+    v11:Nullptr = LoadConst<Nullptr>
+    v12:CInt64 = LoadEvalBreaker
+    CondBranch<2, 1> v12
+  }
+
+  bb 2 (preds 0) {
+    UpdatePrevInstr<idx:0 line_no:1: no parent>
+    v13:CInt32 = RunPeriodicTasks {
+      LiveValues<3> b:v8 b:v9 unc:v11
+      FrameState {
+        CurInstrOffset 0
+        Locals<3> v8 v9 v11
+      }
+    }
+    Branch<1>
+  }
+
+  bb 1 (preds 0, 2) {
+    v17:MortalListExact = MakeList<0> {
+      LiveValues<3> b:v8 b:v9 unc:v11
+      FrameState {
+        CurInstrOffset 4
+        Locals<3> v8 v9 v11
+      }
+    }
+    v18:ImmortalNoneType = ListExtend v17 v8 {
+      LiveValues<4> b:v8 b:v9 unc:v11 o:v17
+      FrameState {
+        CurInstrOffset 8
+        Locals<3> v8 v9 v11
+        Stack<1> v17
+      }
+    }
+    UpdatePrevInstr<idx:7 line_no:3: no parent>
+    Decref v17
+    Incref v9
+    Return v9
+  }
+}
 --- End ---

cinderx/RuntimeTests/hir_tests/builtin_load_method_elimination_test.txt

@@ -792,7 +792,7 @@ fun jittestmodule:test {
     v14:Func = LoadCurrentFunc
     LoadFrame
     Snapshot
-    v15:OptNoneType = InitialYield {
+    v15:OptImmortalNoneType = InitialYield {
       FrameState {
         CurInstrOffset 0
       }
@@ -893,7 +893,7 @@ fun jittestmodule:test {
     v14:Func = LoadCurrentFunc
     LoadFrame
     Snapshot
-    v15:OptNoneType = InitialYield {
+    v15:OptImmortalNoneType = InitialYield {
       FrameState {
         CurInstrOffset 2
       }
@@ -994,7 +994,7 @@ fun jittestmodule:test {
     v15:Func = LoadCurrentFunc
     LoadFrame
     Snapshot
-    v16:OptNoneType = InitialYield {
+    v16:OptImmortalNoneType = InitialYield {
       FrameState {
         CurInstrOffset 2
       }

cinderx/RuntimeTests/hir_tests/inliner_test.txt

@@ -529,7 +529,7 @@ fun jittestmodule:test {
     }
     Snapshot
     v17:MortalTupleExact[tuple:0xdeadbeef] = LoadConst<MortalTupleExact[tuple:0xdeadbeef]>
-    v18:NoneType = ListExtend v16 v17 {
+    v18:ImmortalNoneType = ListExtend v16 v17 {
       FrameState {
         CurInstrOffset 6
         Locals<1> v12
@@ -619,7 +619,7 @@ fun jittestmodule:test {
     }
     Snapshot
     v17:MortalTupleExact[tuple:0xdeadbeef] = LoadConst<MortalTupleExact[tuple:0xdeadbeef]>
-    v18:NoneType = ListExtend v16 v17 {
+    v18:ImmortalNoneType = ListExtend v16 v17 {
       FrameState {
         CurInstrOffset 6
         Locals<1> v12
@@ -710,7 +710,7 @@ fun jittestmodule:test {
     }
     Snapshot
     v17:MortalTupleExact[tuple:0xdeadbeef] = LoadConst<MortalTupleExact[tuple:0xdeadbeef]>
-    v18:NoneType = ListExtend v16 v17 {
+    v18:ImmortalNoneType = ListExtend v16 v17 {
       FrameState {
         CurInstrOffset 8
         Locals<1> v12