[SIL] Added SILType::getLifetime.

The function describes the lifetime that variables of that type have by
default (unless otherwise annotated).  This is done by looking at leaf
nodes until one that is not eager move is found, at which point the
lifetime is known to be lexical.  Otherwise, the lifetime is eager move
(i.e. if every leaf is eager move).

Author: nate-chandler

include/swift/SIL/SILType.h

@@ -20,9 +20,10 @@
 
 #include "swift/AST/SILLayout.h"
 #include "swift/AST/Types.h"
+#include "swift/SIL/Lifetime.h"
+#include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/PointerIntPair.h"
 #include "llvm/Support/ErrorHandling.h"
-#include "llvm/ADT/Hashing.h"
 
 namespace swift {
 
@@ -351,6 +352,15 @@ class SILType {
     return getASTType().hasReferenceSemantics();
   }
 
+  /// The lifetime of values of this type (which are not otherwise annotated).
+  ///
+  /// Trivial types are ::None.
+  /// Non-trivial types are ::Lexical by default.
+  /// Non-trivial types which are annotated @_eagerMove are ::EagerMove.
+  /// Aggregates which consist entirely of ::EagerMove fields are ::EagerMove.
+  /// All other types are ::Lexical.
+  Lifetime getLifetime(const SILFunction &F) const;
+
   /// Returns true if the referenced type is any sort of class-reference type,
   /// meaning anything with reference semantics that is not a function type.
   bool isAnyClassReferenceType() const {

lib/SIL/IR/SILType.cpp

@@ -161,6 +161,15 @@ bool SILType::isNoReturnFunction(SILModule &M,
   return false;
 }
 
+Lifetime SILType::getLifetime(const SILFunction &F) const {
+  auto contextType = hasTypeParameter() ? F.mapTypeIntoContext(*this) : *this;
+  const auto &lowering = F.getTypeLowering(contextType);
+  auto properties = lowering.getRecursiveProperties();
+  if (properties.isTrivial())
+    return Lifetime::None;
+  return properties.isLexical() ? Lifetime::Lexical : Lifetime::EagerMove;
+}
+
 std::string SILType::getMangledName() const {
   Mangle::ASTMangler mangler;
   return mangler.mangleTypeWithoutPrefix(getRawASTType());