Merge pull request #14386 from xwu/no-mixing

[stdlib/Sema] Minor improvements to synthesized hashValue

Author: xwu

lib/Sema/DerivedConformanceEquatableHashable.cpp

@@ -838,7 +838,7 @@ deriveBodyHashable_enum_hashValue(AbstractFunctionDecl *hashValueDecl) {
   for (auto elt : enumDecl->getAllElements()) {
     // case .<elt>(let a0, let a1, ...):
     SmallVector<VarDecl*, 3> payloadVars;
-    SmallVector<ASTNode, 3> mixExpressions;
+    SmallVector<ASTNode, 3> combineExprs;
 
     auto payloadPattern = enumElementPayloadSubpattern(elt, 'a', hashValueDecl,
                                                        payloadVars);
@@ -863,7 +863,7 @@ deriveBodyHashable_enum_hashValue(AbstractFunctionDecl *hashValueDecl) {
                                            /*implicit*/ true);
       auto assignExpr = new (C) AssignExpr(resultRef, SourceLoc(),
                                            ordinalExpr, /*implicit*/ true);
-      mixExpressions.emplace_back(ASTNode(assignExpr));
+      combineExprs.emplace_back(ASTNode(assignExpr));
     }
 
     if (!hasNoAssociatedValues) {
@@ -873,18 +873,14 @@ deriveBodyHashable_enum_hashValue(AbstractFunctionDecl *hashValueDecl) {
         auto payloadVarRef = new (C) DeclRefExpr(payloadVar, DeclNameLoc(),
                                                  /*implicit*/ true);
         // result = _combineHashValues(result, <payloadVar>.hashValue)
-        auto mixExpr = combineHashValuesAssignmentExpr(C, resultVar,
-                                                       payloadVarRef);
-        mixExpressions.emplace_back(ASTNode(mixExpr));
+        auto combineExpr = combineHashValuesAssignmentExpr(C, resultVar,
+                                                           payloadVarRef);
+        combineExprs.emplace_back(ASTNode(combineExpr));
       }
-
-      // result = _mixInt(result)
-      auto assignExpr = mixIntAssignmentExpr(C, resultVar);
-      mixExpressions.emplace_back(ASTNode(assignExpr));
     }
 
     auto hasBoundDecls = !payloadVars.empty();
-    auto body = BraceStmt::create(C, SourceLoc(), mixExpressions, SourceLoc());
+    auto body = BraceStmt::create(C, SourceLoc(), combineExprs, SourceLoc());
     cases.push_back(CaseStmt::create(C, SourceLoc(), labelItem, hasBoundDecls,
                                      SourceLoc(), body));
   }
@@ -963,16 +959,12 @@ deriveBodyHashable_struct_hashValue(AbstractFunctionDecl *hashValueDecl) {
     auto selfPropertyExpr = new (C) DotSyntaxCallExpr(propertyRef, SourceLoc(),
                                                       selfRef);
     // result = _combineHashValues(result, <property>.hashValue)
-    auto mixExpr = combineHashValuesAssignmentExpr(C, resultVar,
-                                                   selfPropertyExpr);
-    statements.emplace_back(ASTNode(mixExpr));
+    auto combineExpr = combineHashValuesAssignmentExpr(C, resultVar,
+                                                       selfPropertyExpr);
+    statements.emplace_back(ASTNode(combineExpr));
   }
 
   {
-    // result = _mixInt(result)
-    auto assignExpr = mixIntAssignmentExpr(C, resultVar);
-    statements.push_back(assignExpr);
-
     // return result
     auto resultRef = new (C) DeclRefExpr(resultVar, DeclNameLoc(),
                                          /*implicit*/ true,
@@ -1021,7 +1013,6 @@ deriveHashable_hashValue(TypeChecker &tc, Decl *parentDecl,
   //       result = _combineHashValues(result, a0.hashValue)
   //       result = _combineHashValues(result, a1.hashValue)
   //     }
-  //     result = _mixInt(result)
   //     return result
   //   }
   // }
@@ -1030,10 +1021,9 @@ deriveHashable_hashValue(TypeChecker &tc, Decl *parentDecl,
   //   var x: Int
   //   var y: String
   //   @derived var hashValue: Int {
-  //     var result: Int = 0
+  //     var result = 0
   //     result = _combineHashValues(result, x.hashValue)
   //     result = _combineHashValues(result, y.hashValue)
-  //     result = _mixInt(result)
   //     return result
   //   }
   // }

stdlib/public/core/DoubleWidth.swift.gyb

@@ -154,7 +154,6 @@ extension DoubleWidth : Hashable {
     var result = 0
     result = _combineHashValues(result, _storage.high.hashValue)
     result = _combineHashValues(result, _storage.low.hashValue)
-    result = _mixInt(result)
     return result
   }
 }

stdlib/public/core/Hashing.swift

@@ -203,7 +203,13 @@ func _squeezeHashValue(_ hashValue: Int, _ upperBound: Int) -> Int {
 @_transparent
 public // @testable
 func _combineHashValues(_ firstValue: Int, _ secondValue: Int) -> Int {
-  let magic = 0x9e3779b9 as UInt // Based on the golden ratio.
+  // Use a magic number based on the golden ratio
+  // (0x1.9e3779b97f4a7c15f39cc0605cedc8341082276bf3a27251f86c6a11d0c18e95p0).
+#if arch(i386) || arch(arm)
+  let magic = 0x9e3779b9 as UInt
+#elseif arch(x86_64) || arch(arm64) || arch(powerpc64) || arch(powerpc64le) || arch(s390x)
+  let magic = 0x9e3779b97f4a7c15 as UInt
+#endif
   var x = UInt(bitPattern: firstValue)
   x ^= UInt(bitPattern: secondValue) &+ magic &+ (x &<< 6) &+ (x &>> 2)
   return Int(bitPattern: x)