GenericSpecializer: fix the function convention if specialization removes the self parameter of a method

When dropping the self metatype parameter of a method, it must become a "thin" function.

Fixes a crash when using performance annotations.

rdar://107202455

Author: eeckstein

lib/SILOptimizer/Utils/Generics.cpp

@@ -1025,12 +1025,16 @@ createSpecializedType(CanSILFunctionType SubstFTy, SILModule &M) const {
     SpecializedResults.push_back(RI);
   }
   unsigned idx = 0;
+  bool removedSelfParam = false;
   for (SILParameterInfo PI : SubstFTy->getParameters()) {
     unsigned paramIdx = idx++;
     PI = PI.getUnsubstituted(M, SubstFTy, context);
 
-    if (isDroppedMetatypeArg(param2ArgIndex(paramIdx)))
+    if (isDroppedMetatypeArg(param2ArgIndex(paramIdx))) {
+      if (SubstFTy->hasSelfParam() && paramIdx == SubstFTy->getParameters().size() - 1)
+        removedSelfParam = true;
       continue;
+    }
 
     bool isTrivial = TrivialArgs.test(param2ArgIndex(paramIdx));
     if (!isParamConverted(paramIdx)) {
@@ -1061,8 +1065,15 @@ createSpecializedType(CanSILFunctionType SubstFTy, SILModule &M) const {
   auto Signature = SubstFTy->isPolymorphic()
                      ? SubstFTy->getInvocationGenericSignature()
                      : CanGenericSignature();
+
+  SILFunctionType::ExtInfo extInfo = SubstFTy->getExtInfo();
+  if (extInfo.hasSelfParam() && removedSelfParam) {
+    extInfo = extInfo.withRepresentation(SILFunctionTypeRepresentation::Thin);
+    assert(!extInfo.hasSelfParam());
+  }
+
   return SILFunctionType::get(
-      Signature, SubstFTy->getExtInfo(),
+      Signature, extInfo,
       SubstFTy->getCoroutineKind(), SubstFTy->getCalleeConvention(),
       SpecializedParams, SpecializedYields, SpecializedResults,
       SubstFTy->getOptionalErrorResult(), SubstitutionMap(), SubstitutionMap(),

test/SILOptimizer/performance-annotations2.swift

@@ -0,0 +1,20 @@
+// RUN: %target-swift-frontend -experimental-performance-annotations %s -sil-verify-all -module-name=test -emit-sil | %FileCheck %s
+
+// REQUIRES: swift_in_compiler,swift_stdlib_no_asserts,optimized_stdlib
+// UNSUPPORTED: swift_test_mode_optimize
+
+public struct Stack<T> {
+    var size = 42
+}
+
+// CHECK-LABEL: sil [no_allocation] @$s4test11createStackyyF :
+// CHECK:         [[F:%[0-9]+]] = function_ref @$s4test5StackVACyxGycfCSi_Tgm5
+// CHECK:         [[S:%[0-9]+]] = apply [[F]]()
+// CHECK:         debug_value [[S]]
+// CHECK:       } // end sil function '$s4test11createStackyyF'
+@_noAllocation
+public func createStack() {
+    let s = Stack<Int>()
+    _ = s.size
+}
+