Make SymInt constructor explicit

Since we plan to have a bunch of code that is sensitive to whether or not a SymInt contains a symbolic shape or not, it seems like a bad idea to have an implicit constructor. For example, code like: ``` sizes_and_strides_.stride_at_unchecked(dim) = 0; ``` would sail through, and the `0` would get implicitly promoted to a SymInt. This is a tradeoff though: it makes code that handles `SymInt`s more clunky as `int64_t`s and integer literals need to be explicitly wrapped in `SymInt` before being used. Pull Request resolved: pytorch#77666 Approved by: https://github.com/ezyang

Author: suo

c10/core/SymInt.h

@@ -31,7 +31,7 @@ class SymbolicIntNode;
 // a traced operation to represent it in LTC or Fx graphs.
 class C10_API SymInt {
  public:
- SymInt(int64_t d) : data_(d){};
+ explicit SymInt(int64_t d) : data_(d){};
 
  int64_t expect_int() const {
  TORCH_CHECK(!is_symbolic());
@@ -51,7 +51,7 @@ class C10_API SymInt {
  TORCH_CHECK(
  !this->is_symbolic() && !sci.is_symbolic(),
  "Symbolic Add isn't supported yet");
- return data_ + sci.data_;
+ return SymInt(data_ + sci.data_);
  }
 
  std::shared_ptr<SymbolicIntNode> toSymbolicIntNode();

test/cpp/jit/test_misc.cpp

@@ -1386,7 +1386,7 @@ TEST(ThreadLocalDebugInfoTest, Basic) {
 TEST(TestSymIntArrayRef, BasicConversion) {
  const size_t X = 2, Y = 4, Z = 5;
  std::vector<int64_t> tgt_size_v{2, 4, 5};
- std::vector<c10::SymInt> tgt_size({X, Y, Z});
+ std::vector<c10::SymInt> tgt_size({SymInt(X), SymInt(Y), SymInt(Z)});
  auto a = at::randn({1, 4, 1}, at::kCPU);
  auto b = a.expand(tgt_size);
  auto c = a.expand(tgt_size_v);

torch/csrc/utils/python_arg_parser.h

@@ -637,7 +637,9 @@ inline int64_t PythonArgs::toInt64(int i) {
 }
 
 inline c10::SymInt PythonArgs::toSymInt(int i) {
- if (!args[i]) return signature.params[i].default_int;
+ if (!args[i]) {
+ return c10::SymInt(signature.params[i].default_int);
+ }
  if (traceable && jit::tracer::isTracing() && THPVariable_Check(args[i])) {
  auto & var = THPVariable_Unpack(args[i]);
  jit::tracer::ArgumentStash::stashValue(