Define cast<i32>(u32) overflow behavior (halide#7769)

uint32 -> int32 casting should not produce SIO

src/Simplify_Cast.cpp

@@ -74,14 +74,21 @@ Expr Simplify::visit(const Cast *op, ExprInfo *bounds) {
  } else if (op->type.is_int() &&
  const_uint(value, &u) &&
  op->type.bits() < value.type().bits()) {
- // uint -> int
+ // uint -> int narrowing
  // Recursively call mutate just to set the bounds
  return mutate(make_const(op->type, safe_numeric_cast<int64_t>(u)), bounds);
  } else if (op->type.is_int() &&
  const_uint(value, &u) &&
- op->type.bits() >= value.type().bits()) {
- // uint -> int with less than or equal to the number of bits
+ op->type.bits() == value.type().bits()) {
+ // uint -> int reinterpret
+ // Recursively call mutate just to set the bounds
+ return mutate(make_const(op->type, safe_numeric_cast<int64_t>(u)), bounds);
+ } else if (op->type.is_int() &&
+ const_uint(value, &u) &&
+ op->type.bits() > value.type().bits()) {
+ // uint -> int widening
  if (op->type.can_represent(u) || op->type.bits() < 32) {
+ // If the type can represent the value or overflow is well-defined.
  // Recursively call mutate just to set the bounds
  return mutate(make_const(op->type, safe_numeric_cast<int64_t>(u)), bounds);
  } else {