AST: Optimize the layout of AvailabilityRange.

`AvailabilityRange` is now being used as a currency type in more of the
compiler, and some of those uses are in permanent `ASTContext` allocations. The
class wraps the `VersionRange` utility, which is itself a wrapper around
`llvm::VersionTuple` with some additional storage for representing sentinel
values. Even though the two sentinel values can be be represented with just a
single bit of additional storage on top of the 16 bytes required to represent
`VersionTuple`, because of alignment requirements the sentinel values end up
bloating the layout of `VersionRange` by many bytes.

To make `AvailabilityRange` and `VersionRange` more efficient to store, we can
instead reserve two unlikely `llvm::VersionTuple` bit patterns as the sentinel
values instead. The values chosen are the same ones LLVM uses to represent
version tuple tombstones and empty keys in a `DenseMap`.

include/swift/AST/ASTBridging.h

@@ -514,7 +514,7 @@ enum ENUM_EXTENSIBILITY_ATTR(open) BridgedDiagID : uint32_t {
 };
 
 class BridgedDiagnosticArgument {
-  int64_t storage[4];
+  int64_t storage[3];
 
 public:
   BRIDGED_INLINE BridgedDiagnosticArgument(const swift::DiagnosticArgument &arg);

include/swift/AST/AvailabilityRange.h

@@ -17,6 +17,7 @@
 #ifndef SWIFT_AST_AVAILABILITY_RANGE_H
 #define SWIFT_AST_AVAILABILITY_RANGE_H
 
+#include "swift/Basic/Assertions.h"
 #include "swift/Basic/LLVM.h"
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/Support/VersionTuple.h"
@@ -36,36 +37,39 @@ class VersionRange {
   //    All: all versions
   //    x.y.x: all versions greater than or equal to x.y.z
 
-  enum class ExtremalRange { Empty, All };
+  /// The sentinel version tuple representing a range containing all versions.
+  constexpr static llvm::VersionTuple getAllTuple() {
+    return llvm::VersionTuple(0x7FFFFFFE);
+  }
+
+  /// The sentinel version tuple representing an empty range.
+  constexpr static llvm::VersionTuple getEmptyTuple() {
+    return llvm::VersionTuple(0x7FFFFFFF);
+  }
 
   // A version range is either an extremal value (Empty, All) or
   // a single version tuple value representing the lower end point x.y.z of a
   // range [x.y.z, +Inf).
-  union {
-    llvm::VersionTuple LowerEndpoint;
-    ExtremalRange ExtremalValue;
-  };
-
-  unsigned HasLowerEndpoint : 1;
+  llvm::VersionTuple LowerEndpoint;
 
 public:
   /// Returns true if the range of versions is empty, or false otherwise.
   bool isEmpty() const {
-    return !HasLowerEndpoint && ExtremalValue == ExtremalRange::Empty;
+    return !hasLowerEndpoint() && LowerEndpoint == getEmptyTuple();
   }
 
   /// Returns true if the range includes all versions, or false otherwise.
   bool isAll() const {
-    return !HasLowerEndpoint && ExtremalValue == ExtremalRange::All;
+    return !hasLowerEndpoint() && LowerEndpoint == getAllTuple();
   }
 
   /// Returns true if the range has a lower end point; that is, if it is of
   /// the form [X, +Inf).
-  bool hasLowerEndpoint() const { return HasLowerEndpoint; }
+  bool hasLowerEndpoint() const { return isValidVersion(LowerEndpoint); }
 
   /// Returns the range's lower endpoint.
   const llvm::VersionTuple &getLowerEndpoint() const {
-    assert(HasLowerEndpoint);
+    assert(hasLowerEndpoint());
     return LowerEndpoint;
   }
 
@@ -124,7 +128,7 @@ public:
     const llvm::VersionTuple maxVersion =
         std::max(this->getLowerEndpoint(), Other.getLowerEndpoint());
 
-    setLowerEndpoint(maxVersion);
+    LowerEndpoint = maxVersion;
   }
 
   /// Mutates this range to be the union of itself and Other. This is the
@@ -145,7 +149,7 @@ public:
     const llvm::VersionTuple minVersion =
         std::min(this->getLowerEndpoint(), Other.getLowerEndpoint());
 
-    setLowerEndpoint(minVersion);
+    LowerEndpoint = minVersion;
   }
 
   /// Mutates this range to be a best effort over-approximation of the
@@ -160,37 +164,29 @@ public:
   }
 
   /// Returns a version range representing all versions.
-  static VersionRange all() { return VersionRange(ExtremalRange::All); }
+  static VersionRange all() { return VersionRange(getAllTuple()); }
 
   /// Returns a version range representing no versions.
-  static VersionRange empty() { return VersionRange(ExtremalRange::Empty); }
+  static VersionRange empty() { return VersionRange(getEmptyTuple()); }
+
+  /// Returns false if the given version tuple cannot be used as a lower
+  /// endpoint for `VersionRange`.
+  static bool isValidVersion(const llvm::VersionTuple &EndPoint) {
+    return EndPoint != getAllTuple() && EndPoint != getEmptyTuple();
+  }
 
   /// Returns a version range representing all versions greater than or equal
   /// to the passed-in version.
   static VersionRange allGTE(const llvm::VersionTuple &EndPoint) {
+    ASSERT(isValidVersion(EndPoint));
     return VersionRange(EndPoint);
   }
 
   void Profile(llvm::FoldingSetNodeID &ID) const;
 
 private:
-  VersionRange(const llvm::VersionTuple &LowerEndpoint) {
-    setLowerEndpoint(LowerEndpoint);
-  }
-
-  VersionRange(ExtremalRange ExtremalValue) {
-    setExtremalRange(ExtremalValue);
-  }
-
-  void setExtremalRange(ExtremalRange Version) {
-    HasLowerEndpoint = 0;
-    ExtremalValue = Version;
-  }
-
-  void setLowerEndpoint(const llvm::VersionTuple &Version) {
-    HasLowerEndpoint = 1;
-    LowerEndpoint = Version;
-  }
+  VersionRange(const llvm::VersionTuple &LowerEndpoint)
+      : LowerEndpoint(LowerEndpoint) {}
 };
 
 /// Represents a version range in which something is available.
@@ -327,7 +323,7 @@ public:
   /// Returns a representation of the raw version range as a string for
   /// debugging purposes.
   std::string getVersionString() const {
-    assert(Range.hasLowerEndpoint());
+    ASSERT(Range.hasLowerEndpoint());
     return Range.getLowerEndpoint().getAsString();
   }
 };

include/swift/AST/DiagnosticsSema.def

@@ -6754,6 +6754,8 @@ WARNING(availability_suggest_platform_name,
         PointsToFirstBadToken, "unrecognized platform name %0;"
         " did you mean '%1'?",
         (Identifier, StringRef))
+WARNING(availability_unsupported_version_number, none,
+        "'%0' is not a supported version number", (llvm::VersionTuple))
 
 WARNING(attr_availability_expected_deprecated_version, none,
        "expected version number with 'deprecated' in '%0' attribute for %1",

lib/AST/Availability.cpp

@@ -769,7 +769,25 @@ SemanticAvailableAttrRequest::evaluate(swift::Evaluator &evaluator,
   if (!domain)
     return std::nullopt;
 
-  auto semanticAttr = SemanticAvailableAttr(attr);
+  auto checkVersion = [&](std::optional<llvm::VersionTuple> version,
+                          SourceRange sourceRange) {
+    if (version && !VersionRange::isValidVersion(*version)) {
+      diags
+          .diagnose(attrLoc, diag::availability_unsupported_version_number,
+                    *version)
+          .highlight(sourceRange);
+      return true;
+    }
+
+    return false;
+  };
+
+  if (checkVersion(attr->getRawIntroduced(), attr->IntroducedRange))
+    return std::nullopt;
+  if (checkVersion(attr->getRawDeprecated(), attr->DeprecatedRange))
+    return std::nullopt;
+  if (checkVersion(attr->getRawObsoleted(), attr->ObsoletedRange))
+    return std::nullopt;
 
   bool hasIntroduced = attr->getRawIntroduced().has_value();
   bool hasDeprecated = attr->getRawDeprecated().has_value();
@@ -779,11 +797,11 @@ SemanticAvailableAttrRequest::evaluate(swift::Evaluator &evaluator,
   if (!domain->isVersioned() && hasVersionSpec) {
     SourceRange versionSourceRange;
     if (hasIntroduced)
-      versionSourceRange = semanticAttr.getIntroducedSourceRange();
+      versionSourceRange = attr->IntroducedRange;
     else if (hasDeprecated)
-      versionSourceRange = semanticAttr.getDeprecatedSourceRange();
+      versionSourceRange = attr->DeprecatedRange;
     else if (hasObsoleted)
-      versionSourceRange = semanticAttr.getObsoletedSourceRange();
+      versionSourceRange = attr->ObsoletedRange;
 
     diags.diagnose(attrLoc, diag::availability_unexpected_version, *domain)
         .limitBehaviorIf(domain->isUniversal(), DiagnosticBehavior::Warning)
@@ -827,7 +845,7 @@ SemanticAvailableAttrRequest::evaluate(swift::Evaluator &evaluator,
     }
   }
 
-  return semanticAttr;
+  return SemanticAvailableAttr(attr);
 }
 
 std::optional<llvm::VersionTuple> SemanticAvailableAttr::getIntroduced() const {

lib/AST/AvailabilitySpec.cpp

@@ -17,7 +17,7 @@
 #include "swift/AST/AvailabilitySpec.h"
 #include "swift/AST/ASTContext.h"
 #include "swift/AST/AvailabilityDomain.h"
-#include "swift/AST/DiagnosticsParse.h"
+#include "swift/AST/DiagnosticsSema.h"
 #include "swift/AST/TypeCheckRequests.h"
 #include "llvm/Support/raw_ostream.h"
 
@@ -116,21 +116,35 @@ std::optional<SemanticAvailabilitySpec>
 SemanticAvailabilitySpecRequest::evaluate(
     Evaluator &evaluator, const AvailabilitySpec *spec,
     const DeclContext *declContext) const {
+  if (spec->isInvalid())
+    return std::nullopt;
+
+  auto &diags = declContext->getASTContext().Diags;
   AvailabilitySpec *mutableSpec = const_cast<AvailabilitySpec *>(spec);
-  if (mutableSpec->resolveInDeclContext(declContext).has_value())
-    return SemanticAvailabilitySpec(spec);
-  return std::nullopt;
+  if (!mutableSpec->resolveInDeclContext(declContext).has_value())
+    return std::nullopt;
+
+  auto version = spec->getRawVersion();
+  if (!VersionRange::isValidVersion(version)) {
+    diags
+        .diagnose(spec->getStartLoc(),
+                  diag::availability_unsupported_version_number, version)
+        .highlight(spec->getVersionSrcRange());
+    return std::nullopt;
+  }
+
+  return SemanticAvailabilitySpec(spec);
 }
 
 std::optional<std::optional<SemanticAvailabilitySpec>>
 SemanticAvailabilitySpecRequest::getCachedResult() const {
   auto *spec = std::get<0>(getStorage());
+  if (spec->isInvalid())
+    return std::optional<SemanticAvailabilitySpec>();
+
   auto domainOrIdentifier = spec->getDomainOrIdentifier();
   if (!domainOrIdentifier.isResolved())
-    return {};
-
-  if (spec->isInvalid())
-    return {std::nullopt};
+    return std::nullopt;
 
   return SemanticAvailabilitySpec(spec);
 }

lib/Sema/MiscDiagnostics.cpp

@@ -5158,6 +5158,17 @@ static bool diagnoseAvailabilityCondition(PoundAvailableInfo *info,
       return true;
     }
 
+    if (hasVersion) {
+      auto rawVersion = parsedSpec->getRawVersion();
+      if (!VersionRange::isValidVersion(rawVersion)) {
+        diags
+            .diagnose(loc, diag::availability_unsupported_version_number,
+                      rawVersion)
+            .highlight(parsedSpec->getVersionSrcRange());
+        return true;
+      }
+    }
+
     if (domain.isVersioned()) {
       if (!hasVersion) {
         diags.diagnose(loc, diag::avail_query_expected_version_number);

test/Sema/availability_versions_unsupported.swift

@@ -0,0 +1,44 @@
+// RUN: %target-typecheck-verify-swift
+
+@available(macOS, introduced: 2147483646) // expected-warning {{'2147483646' is not a supported version number}}
+func funcIntroducedInMacOS2147483646() { }
+
+@available(macOS 2147483646, *) // expected-warning {{'2147483646' is not a supported version number}}
+func funcIntroducedInMacOS2147483646Short() { }
+
+@available(macOS, deprecated: 2147483646) // expected-warning {{'2147483646' is not a supported version number}}
+func funcDeprecatedInMacOS2147483646() { }
+
+@available(macOS, obsoleted: 2147483646) // expected-warning {{'2147483646' is not a supported version number}}
+func funcObsoletedInMacOS2147483646() { }
+
+@available(macOS, introduced: 2147483647) // expected-warning {{'2147483647' is not a supported version number}}
+func funcIntroducedInMacOS2147483647() { }
+
+@available(macOS 2147483647, *) // expected-warning {{'2147483647' is not a supported version number}}
+func funcIntroducedInMacOS2147483647Short() { }
+
+@available(macOS, deprecated: 2147483647) // expected-warning {{'2147483647' is not a supported version number}}
+func funcDeprecatedInMacOS2147483647() { }
+
+@available(macOS, obsoleted: 2147483647) // expected-warning {{'2147483647' is not a supported version number}}
+func funcObsoletedInMacOS2147483647() { }
+
+@available(swift, introduced: 2147483646) // expected-warning {{'2147483646' is not a supported version number}}
+func funcIntroducedInSwift2147483646() { }
+
+func useExtremeVersions() {
+  if #available(macOS 2147483646, *) { // expected-warning {{'2147483646' is not a supported version number}}
+    funcIntroducedInMacOS2147483646()
+    funcIntroducedInMacOS2147483646Short()
+    funcDeprecatedInMacOS2147483646()
+    funcObsoletedInMacOS2147483646()
+  }
+  if #available(macOS 2147483647, *) { // expected-warning {{'2147483647' is not a supported version number}}
+    funcIntroducedInMacOS2147483647()
+    funcIntroducedInMacOS2147483647Short()
+    funcDeprecatedInMacOS2147483647()
+    funcObsoletedInMacOS2147483647()
+  }
+  funcIntroducedInSwift2147483646()
+}

test/attr/attr_availability.swift

@@ -155,6 +155,12 @@ let _: Int
 @available(OSX, introduced: 0.0.0) // expected-warning{{expected version number in 'available' attribute; this is an error in the Swift 6 language mode}}
 let _: Int
 
+@available(OSX, introduced: 2147483646)
+let _: Int
+
+@available(OSX, introduced: 2147483647)
+let _: Int
+
 @available(*, renamed: "bad name") // expected-error{{'renamed' argument of 'available' attribute must be an operator, identifier, or full function name, optionally prefixed by a type name}}
 let _: Int
 

unittests/AST/VersionRangeTests.cpp

@@ -125,3 +125,9 @@ TEST_F(VersionRangeLattice, JoinWithClosedEndedPositiveInfinity) {
   EXPECT_TRUE(unionEquals(GreaterThanEqual10_10, GreaterThanEqual10_9,
                           GreaterThanEqual10_9));
 }
+
+TEST_F(VersionRangeLattice, ValidVersionTuples) {
+  EXPECT_TRUE(VersionRange::isValidVersion(llvm::VersionTuple()));
+  EXPECT_FALSE(VersionRange::isValidVersion(llvm::VersionTuple(0x7FFFFFFE)));
+  EXPECT_FALSE(VersionRange::isValidVersion(llvm::VersionTuple(0x7FFFFFFF)));
+}