[Lang] add option short_circuit_operators for shor-circuiting boole…

…an ops (taichi-dev#3572)

python/taichi/lang/__init__.py

@@ -421,6 +421,7 @@ def __init__(self):
         self.gdb_trigger = False
         self.excepthook = False
         self.experimental_real_function = False
+        self.short_circuit_operators = False
 
 
 def prepare_sandbox():
@@ -591,6 +592,7 @@ def init(arch=None,
     env_spec.add('gdb_trigger')
     env_spec.add('excepthook')
     env_spec.add('experimental_real_function')
+    env_spec.add('short_circuit_operators')
 
     # compiler configurations (ti.cfg):
     for key in dir(ti.cfg):
@@ -620,6 +622,8 @@ def init(arch=None,
         impl.get_runtime().print_preprocessed = spec_cfg.print_preprocessed
         impl.get_runtime().experimental_real_function = \
             spec_cfg.experimental_real_function
+        impl.get_runtime().short_circuit_operators = \
+            spec_cfg.short_circuit_operators
         ti.set_logging_level(spec_cfg.log_level.lower())
         if spec_cfg.excepthook:
             # TODO(#1405): add a way to restore old excepthook

python/taichi/lang/ast/ast_transformer.py

@@ -476,17 +476,68 @@ def build_UnaryOp(ctx, node):
         node.ptr = op(node.operand.ptr)
         return node
 
+    @staticmethod
+    def build_short_circuit_and(operands):
+        if len(operands) == 1:
+            return operands[0].ptr
+
+        val = ti.expr_init(None)
+        lhs = operands[0].ptr
+        ti.begin_frontend_if(lhs)
+
+        ti.core.begin_frontend_if_true()
+        rhs = ASTTransformer.build_short_circuit_and(operands[1:])
+        val.assign(rhs)
+        ti.core.pop_scope()
+
+        ti.core.begin_frontend_if_false()
+        val.assign(0)
+        ti.core.pop_scope()
+
+        return val
+
+    @staticmethod
+    def build_short_circuit_or(operands):
+        if len(operands) == 1:
+            return operands[0].ptr
+
+        val = ti.expr_init(None)
+        lhs = operands[0].ptr
+        ti.begin_frontend_if(lhs)
+
+        ti.core.begin_frontend_if_true()
+        val.assign(1)
+        ti.core.pop_scope()
+
+        ti.core.begin_frontend_if_false()
+        rhs = ASTTransformer.build_short_circuit_or(operands[1:])
+        val.assign(rhs)
+        ti.core.pop_scope()
+
+        return val
+
+    @staticmethod
+    def build_normal_bool_op(op):
+        def inner(operands):
+            result = op(operands[0].ptr, operands[1].ptr)
+            for i in range(2, len(operands)):
+                result = op(result, operands[i].ptr)
+            return result
+
+        return inner
+
     @staticmethod
     def build_BoolOp(ctx, node):
         node.values = build_stmts(ctx, node.values)
-        op = {
-            ast.And: ti.logical_and,
-            ast.Or: ti.logical_or,
-        }.get(type(node.op))
-        result = op(node.values[0].ptr, node.values[1].ptr)
-        for i in range(2, len(node.values)):
-            result = op(result, node.values[i].ptr)
-        node.ptr = result
+        ops = {
+            ast.And: ASTTransformer.build_short_circuit_and,
+            ast.Or: ASTTransformer.build_short_circuit_or,
+        } if impl.get_runtime().short_circuit_operators else {
+            ast.And: ASTTransformer.build_normal_bool_op(ti.logical_and),
+            ast.Or: ASTTransformer.build_normal_bool_op(ti.logical_or),
+        }
+        op = ops.get(type(node.op))
+        node.ptr = op(node.values)
         return node
 
     @staticmethod

tests/python/test_short_circuit.py

@@ -0,0 +1,49 @@
+import taichi as ti
+
+
+@ti.test(debug=True, short_circuit_operators=True)
+def test_and_shorted():
+    a = ti.field(ti.i32, shape=10)
+
+    @ti.func
+    def explode() -> ti.i32:
+        return a[-1]
+
+    @ti.kernel
+    def func() -> ti.i32:
+        return False and explode()
+
+    assert func() == 0
+
+
+@ti.test(debug=True, short_circuit_operators=True)
+def test_and_not_shorted():
+    @ti.kernel
+    def func() -> ti.i32:
+        return True and False
+
+    assert func() == 0
+
+
+@ti.test(debug=True, short_circuit_operators=True)
+def test_or_shorted():
+    a = ti.field(ti.i32, shape=10)
+
+    @ti.func
+    def explode() -> ti.i32:
+        return a[-1]
+
+    @ti.kernel
+    def func() -> ti.i32:
+        return True or explode()
+
+    assert func() == 1
+
+
+@ti.test(debug=True, short_circuit_operators=True)
+def test_or_not_shorted():
+    @ti.kernel
+    def func() -> ti.i32:
+        return False or True
+
+    assert func() == 1