IRGen: Don't use relative pointers for value witness tables under relative procotol witness tables mode

Author: aschwaighofer

lib/IRGen/GenOpaque.cpp

@@ -334,25 +334,34 @@ Address irgen::slotForLoadOfOpaqueWitness(IRGenFunction &IGF,
 /// Load a specific witness from a known table.  The result is
 /// always an i8*.
 llvm::Value *irgen::emitInvariantLoadOfOpaqueWitness(IRGenFunction &IGF,
+                                                     bool isProtocolWitness,
                                                      llvm::Value *table,
                                                      WitnessIndex index,
                                                      llvm::Value **slotPtr) {
-  auto isRelativeTable = IGF.IGM.IRGen.Opts.UseRelativeProtocolWitnessTables;
+  // Is this is a load of a relative protocol witness table entry.
+  auto isRelativeTable = IGF.IGM.IRGen.Opts.UseRelativeProtocolWitnessTables &&
+    isProtocolWitness;
+
   auto slot = slotForLoadOfOpaqueWitness(IGF, table, index, isRelativeTable);
   if (slotPtr) *slotPtr = slot.getAddress();
+
   if (isRelativeTable) {
     return IGF.emitLoadOfRelativePointer(slot, false, IGF.IGM.Int8Ty);
   }
+
   return IGF.emitInvariantLoad(slot);
 }
 
 /// Load a specific witness from a known table.  The result is
 /// always an i8*.
 llvm::Value *irgen::emitInvariantLoadOfOpaqueWitness(IRGenFunction &IGF,
+                                                     bool isProtocolWitness,
                                                      llvm::Value *table,
                                                      llvm::Value *index,
                                                      llvm::Value **slotPtr) {
   assert(table->getType() == IGF.IGM.WitnessTablePtrTy);
+  assert(!isProtocolWitness &&
+         "This function does not yet support relative protocol witnesses");
 
   // GEP to the appropriate index.
   llvm::Value *slot =
@@ -438,7 +447,8 @@ static FunctionPointer emitLoadOfValueWitnessFunction(IRGenFunction &IGF,
 
   llvm::Value *slot;
   llvm::Value *witness =
-    emitInvariantLoadOfOpaqueWitness(IGF, table, windex, &slot);
+    emitInvariantLoadOfOpaqueWitness(IGF, /*isProtocolWitness*/false, table,
+                                     windex, &slot);
   auto label = getValueWitnessLabel(index);
   auto signature = IGF.IGM.getValueWitnessSignature(index);
 

lib/IRGen/GenOpaque.h

@@ -52,6 +52,7 @@ namespace irgen {
   /// The load is marked invariant. This should not be used in contexts where
   /// the referenced witness table is still undergoing initialization.
   llvm::Value *emitInvariantLoadOfOpaqueWitness(IRGenFunction &IGF,
+                                                bool isProtocolWitness,
                                                 llvm::Value *table,
                                                 WitnessIndex index,
                                                 llvm::Value **slot = nullptr);
@@ -62,6 +63,7 @@ namespace irgen {
   /// The load is marked invariant. This should not be used in contexts where
   /// the referenced witness table is still undergoing initialization.
   llvm::Value *emitInvariantLoadOfOpaqueWitness(IRGenFunction &IGF,
+                                                bool isProtocolWitness,
                                                 llvm::Value *table,
                                                 llvm::Value *index,
                                                 llvm::Value **slot = nullptr);

lib/IRGen/GenProto.cpp

@@ -2634,7 +2634,8 @@ llvm::Value *irgen::loadParentProtocolWitnessTable(IRGenFunction &IGF,
   auto &IGM = IGF.IGM;
   if (!IGM.IRGen.Opts.UseRelativeProtocolWitnessTables) {
     auto baseWTable =
-      emitInvariantLoadOfOpaqueWitness(IGF, wtable, index);
+      emitInvariantLoadOfOpaqueWitness(IGF,/*isProtocolWitness*/true, wtable,
+                                       index);
     return baseWTable;
   }
   auto &Builder = IGF.Builder;
@@ -2659,7 +2660,8 @@ llvm::Value *irgen::loadParentProtocolWitnessTable(IRGenFunction &IGF,
 
   Builder.emitBlock(isNotCondBB);
   auto baseWTable2 =
-      emitInvariantLoadOfOpaqueWitness(IGF, wtable, index);
+      emitInvariantLoadOfOpaqueWitness(IGF,/*isProtocolWitness*/true, wtable,
+                                       index);
   baseWTable2 = IGF.Builder.CreateBitCast(baseWTable2,
                                           IGF.IGM.WitnessTablePtrTy);
   Builder.CreateBr(endBB);
@@ -2677,7 +2679,8 @@ llvm::Value *irgen::loadConditionalConformance(IRGenFunction &IGF,
 
   auto &IGM = IGF.IGM;
   if (!IGM.IRGen.Opts.UseRelativeProtocolWitnessTables) {
-    return emitInvariantLoadOfOpaqueWitness(IGF, wtable, index);
+    return emitInvariantLoadOfOpaqueWitness(IGF, /*isProtocolWitness*/true,
+                                            wtable, index);
   }
 
   auto &Builder = IGF.Builder;

test/IRGen/relative_protocol_witness_table.swift

@@ -3,6 +3,10 @@
 // REQUIRES: CPU=x86_64 || CPU=arm64
 // UNSUPPORTED: CPU=arm64e
 
+func testVWT<T>(_ t: T) {
+  var local = t
+}
+
 protocol FuncOnly {
     func a()
     func b()
@@ -185,6 +189,18 @@ func instantiate_conditional_conformance_2nd<T>(_ t : T)  where T: Sub, T.S == T
 // CHECK-SAME:                      i64 ptrtoint (i32* getelementptr inbounds ([4 x i32], [4 x i32]* @"$s1A17ConditionalStructVyxGAA20WithAssocConformanceA2A8FuncOnlyRzAA5InitPRzlWP", i32 0, i32 3) to i64)) to i32)
 // CHECK-SAME: ], align 8
 
+// Make sure value witness table lookup is done right.
+
+// CHECK: define{{.*}} swiftcc void @"$s1A7testVWTyyxlF"(%swift.opaque* {{.*}}, %swift.type* [[T:%.*]])
+// CHECK:  [[T0:%.*]] = bitcast %swift.type* [[T]] to i8***
+// CHECK:  [[VWT_ADDR:%.*]] = getelementptr inbounds i8**, i8*** [[T0]], i64 -1
+// CHECK:  [[VWT_PTR:%.*]] = load i8**, i8*** [[VWT_ADDR]]
+// CHECK:  [[T1:%.*]] = getelementptr inbounds i8*, i8** [[VWT_PTR]], i32 2
+// CHECK:  [[T2:%.*]] = load i8*, i8** [[T1]]
+// CHECK:  [[T3:%.*]] = bitcast i8* [[T2]] to %swift.opaque* (%swift.opaque*, %swift.opaque*, %swift.type*)*
+// CHECK:  call %swift.opaque* [[T3]](%swift.opaque* {{.*}}, %swift.opaque* {{.*}}, %swift.type* [[T]])
+
+
 // Simple witness entry access.
 
 // CHECK: define{{.*}} swiftcc void @"$s1A14requireWitnessyyxAA8FuncOnlyRzlF"(%swift.opaque* noalias nocapture {{%.*}}, %swift.type* {{%.*}}, i8** [[PWT:%.*]])