Fix DIP1008

Invoke _d_newThrowable for exception allocation & initialization, and
increase the reference count in LDC-specific _d_throw_exception for MSVC
targets. Fixes runnable/test19317.d.

gen/classes.cpp

@@ -82,6 +82,7 @@ DValue *DtoNewClass(Loc &loc, TypeClass *tc, NewExp *newexp) {
 
   // allocate
   LLValue *mem;
+  bool doInit = true;
   if (newexp->onstack) {
     unsigned alignment = tc->sym->alignsize;
     if (alignment == STRUCTALIGN_DEFAULT)
@@ -98,17 +99,23 @@ DValue *DtoNewClass(Loc &loc, TypeClass *tc, NewExp *newexp) {
   }
   // default allocator
   else {
-    llvm::Function *fn =
-        getRuntimeFunction(loc, gIR->module, "_d_allocclass");
+    const bool useEHAlloc = global.params.ehnogc && newexp->thrownew;
+    llvm::Function *fn = getRuntimeFunction(
+        loc, gIR->module, useEHAlloc ? "_d_newThrowable" : "_d_allocclass");
     LLConstant *ci = DtoBitCast(getIrAggr(tc->sym)->getClassInfoSymbol(),
                                 DtoType(getClassInfoType()));
-    mem =
-        gIR->CreateCallOrInvoke(fn, ci, ".newclass_gc_alloc").getInstruction();
-    mem = DtoBitCast(mem, DtoType(tc), ".newclass_gc");
+    mem = gIR->CreateCallOrInvoke(fn, ci,
+                                  useEHAlloc ? ".newthrowable_alloc"
+                                             : ".newclass_gc_alloc")
+              .getInstruction();
+    mem = DtoBitCast(mem, DtoType(tc),
+                     useEHAlloc ? ".newthrowable" : ".newclass_gc");
+    doInit = !useEHAlloc;
   }
 
   // init
-  DtoInitClass(tc, mem);
+  if (doInit)
+    DtoInitClass(tc, mem);
 
   // init inner-class outer reference
   if (newexp->thisexp) {

gen/runtime.cpp

@@ -615,6 +615,10 @@ static void buildRuntimeModule() {
   createFwdDecl(LINKc, objectTy, {"_d_newclass", "_d_allocclass"},
                 {classInfoTy}, {STCconst}, Attr_NoAlias);
 
+  // Throwable _d_newThrowable(const ClassInfo ci)
+  createFwdDecl(LINKc, throwableTy, {"_d_newThrowable"}, {classInfoTy},
+                {STCconst}, Attr_NoAlias);
+
   // void* _d_newitemT (TypeInfo ti)
   // void* _d_newitemiT(TypeInfo ti)
   createFwdDecl(LINKc, voidPtrTy, {"_d_newitemT", "_d_newitemiT"}, {typeInfoTy},