MandatoryPerformanceOptimizations: don't de-virtualize a generic class method call to specialized method

This results in wrong argument/return calling conventions.
First, the method call must be specialized. Only then the call can be de-virtualized.
Usually, it's done in this order anyway, because the `class_method` instruction is located before the `apply`.
But when inlining functions, the order (in the worklist) can be the other way round.

Fixes a compiler crash.
rdar://154631438

Author: eeckstein

include/swift/SILOptimizer/Utils/Devirtualize.h

@@ -76,7 +76,7 @@ bool canDevirtualizeClassMethod(FullApplySite AI, ClassDecl *CD,
                                 CanType ClassType,
                                 OptRemark::Emitter *ORE = nullptr,
                                 bool isEffectivelyFinalMethod = false);
-SILFunction *getTargetClassMethod(SILModule &M, ClassDecl *CD,
+SILFunction *getTargetClassMethod(SILModule &M, FullApplySite as, ClassDecl *CD,
                                   CanType ClassType, MethodInst *MI);
 CanType getSelfInstanceType(CanType ClassOrMetatypeType);
 

lib/SILOptimizer/Transforms/SpeculativeDevirtualizer.cpp

@@ -446,7 +446,7 @@ static bool tryToSpeculateTarget(SILPassManager *pm, FullApplySite AI, ClassHier
 
   // Try to devirtualize the static class of instance
   // if it is possible.
-  if (auto F = getTargetClassMethod(M, CD, ClassType, CMI)) {
+  if (auto F = getTargetClassMethod(M, AI, CD, ClassType, CMI)) {
     // Do not devirtualize if a method in the base class is marked
     // as non-optimizable. This way it is easy to disable the
     // devirtualization of this method in the base class and

lib/SILOptimizer/Utils/Devirtualize.cpp

@@ -718,7 +718,7 @@ void swift::deleteDevirtualizedApply(ApplySite old) {
   recursivelyDeleteTriviallyDeadInstructions(oldApply, true);
 }
 
-SILFunction *swift::getTargetClassMethod(SILModule &module, ClassDecl *cd,
+SILFunction *swift::getTargetClassMethod(SILModule &module, FullApplySite as, ClassDecl *cd,
                                          CanType classType, MethodInst *mi) {
   assert((isa<ClassMethodInst>(mi) || isa<SuperMethodInst>(mi)) &&
          "Only class_method and super_method instructions are supported");
@@ -727,6 +727,11 @@ SILFunction *swift::getTargetClassMethod(SILModule &module, ClassDecl *cd,
 
   SILType silType = SILType::getPrimitiveObjectType(classType);
   if (auto *vtable = module.lookUpSpecializedVTable(silType)) {
+    // We cannot de-virtualize a generic method call to a specialized method.
+    // This would result in wrong argument/return calling conventions.
+    if (as.getSubstitutionMap().hasAnySubstitutableParams())
+      return nullptr;
+
     return vtable->getEntry(module, member)->getImplementation();
   }
 
@@ -763,7 +768,7 @@ bool swift::canDevirtualizeClassMethod(FullApplySite applySite, ClassDecl *cd,
   auto *mi = cast<MethodInst>(applySite.getCallee());
 
   // Find the implementation of the member which should be invoked.
-  auto *f = getTargetClassMethod(module, cd, classType, mi);
+  auto *f = getTargetClassMethod(module, applySite, cd, classType, mi);
 
   // If we do not find any such function, we have no function to devirtualize
   // to... so bail.
@@ -849,7 +854,7 @@ swift::devirtualizeClassMethod(SILPassManager *pm, FullApplySite applySite,
   SILModule &module = applySite.getModule();
   auto *mi = cast<MethodInst>(applySite.getCallee());
 
-  auto *f = getTargetClassMethod(module, cd, classType, mi);
+  auto *f = getTargetClassMethod(module, applySite, cd, classType, mi);
 
   CanSILFunctionType genCalleeType = f->getLoweredFunctionTypeInContext(
       TypeExpansionContext(*applySite.getFunction()));

test/embedded/devirt_generic_class_methods.swift

@@ -0,0 +1,22 @@
+// RUN: %target-swift-frontend %s -parse-as-library -enable-experimental-feature Embedded -Xllvm -sil-disable-pass=mandatory-inlining -emit-ir -o /dev/null
+
+// REQUIRES: swift_feature_Embedded
+
+
+// Check that the compiler doesn't crash
+
+public class Base<T> {
+  func foo(_ t: T) -> T {
+    return t
+  }
+}
+
+@_transparent
+func callee(_ i: Int, _ c: Base<Int>) -> Int {
+  return c.foo(i)
+}
+
+public func testit(_ i : Int) -> Int {
+  return callee(i, Base<Int>())
+}
+