Rename DtoIsPassedByRef() to DtoIsInMemoryOnly()

Motivation: issue #937

gen/abi-generic.h

@@ -203,7 +203,7 @@ struct ExplicitByvalRewrite : ABIRewrite {
   }
 
   LLValue *put(DValue *v) override {
-    if (DtoIsPassedByRef(v->getType())) {
+    if (DtoIsInMemoryOnly(v->getType())) {
       LLValue *originalPointer = v->getRVal();
       LLType *type = originalPointer->getType()->getPointerElementType();
       LLValue *copyForCallee =

gen/abi.cpp

@@ -38,7 +38,7 @@ void ABIRewrite::getL(Type *dty, LLValue *v, LLValue *lval) {
 
 LLValue *ABIRewrite::getAddressOf(DValue *v) {
   Type *dty = v->getType();
-  if (DtoIsPassedByRef(dty)) {
+  if (DtoIsInMemoryOnly(dty)) {
     // v is lowered to a LL pointer to the struct/static array
     return v->getRVal();
   }

gen/dvalue.cpp

@@ -67,7 +67,7 @@ LLValue *DVarValue::getRVal() {
     storage = DtoLoad(storage);
   }
 
-  if (DtoIsPassedByRef(type->toBasetype())) {
+  if (DtoIsInMemoryOnly(type->toBasetype())) {
     return storage;
   }
 

gen/functions.cpp

@@ -951,7 +951,7 @@ DValue *DtoArgument(Parameter *fnarg, Expression *argexp) {
   }
 
   // byval arg, but expr has no storage yet
-  if (DtoIsPassedByRef(argexp->type) && (arg->isSlice() || arg->isNull())) {
+  if (DtoIsInMemoryOnly(argexp->type) && (arg->isSlice() || arg->isNull())) {
     LLValue *alloc = DtoAlloca(argexp->type, ".tmp_arg");
     auto vv = new DVarValue(argexp->type, alloc);
     DtoAssign(argexp->loc, vv, arg);

gen/llvmhelpers.cpp

@@ -1346,7 +1346,7 @@ LLValue *makeLValue(Loc &loc, DValue *value) {
   LLValue *valuePointer;
   if (value->isIm()) {
     valuePointer = value->getRVal();
-    needsMemory = !DtoIsPassedByRef(valueType);
+    needsMemory = !DtoIsInMemoryOnly(valueType);
   } else if (value->isVar()) {
     valuePointer = value->getLVal();
     needsMemory = false;
@@ -1533,7 +1533,7 @@ DValue *DtoSymbolAddress(Loc &loc, Type *type, Declaration *decl) {
         assert(type->ty == Tdelegate);
         return new DVarValue(type, getIrValue(vd));
       }
-      if (vd->isRef() || vd->isOut() || DtoIsPassedByRef(vd->type) ||
+      if (vd->isRef() || vd->isOut() || DtoIsInMemoryOnly(vd->type) ||
           llvm::isa<llvm::AllocaInst>(getIrValue(vd))) {
         return new DVarValue(type, vd, getIrValue(vd));
       }

gen/tocall.cpp

@@ -172,7 +172,7 @@ static void addExplicitArguments(std::vector<LLValue *> &args, AttrSet &attrs,
     // Hack around LDC assuming structs and static arrays are in memory:
     // If the function wants a struct, and the argument value is a
     // pointer to a struct, load from it before passing it in.
-    if (isaPointer(llVal) && DtoIsPassedByRef(argType) &&
+    if (isaPointer(llVal) && DtoIsInMemoryOnly(argType) &&
         ((!isVararg && !isaPointer(callableArgType)) ||
          (isVararg && !irArg->byref && !irArg->isByVal()))) {
       Logger::println("Loading struct type for function argument");
@@ -297,7 +297,7 @@ bool DtoLowerMagicIntrinsic(IRState *p, FuncDeclaration *fndecl, CallExp *e,
     LLValue *pAp = toElem((*e->arguments)[0])->getLVal(); // va_list*
     LLValue *vaArgArg = gABI->prepareVaArg(pAp);
     LLType *llType = DtoType(e->type);
-    if (DtoIsPassedByRef(e->type)) {
+    if (DtoIsInMemoryOnly(e->type)) {
       llType = getPtrToType(llType);
     }
     result = new DImValue(e->type, p->ir->CreateVAArg(vaArgArg, llType));

gen/toir.cpp

@@ -2822,7 +2822,7 @@ public:
       Expression *el = (*e->exps)[i];
       DValue *ep = toElem(el);
       LLValue *gep = DtoGEPi(val, 0, i);
-      if (DtoIsPassedByRef(el->type)) {
+      if (DtoIsInMemoryOnly(el->type)) {
         DtoStore(DtoLoad(ep->getRVal()), gep);
       } else if (el->type->ty != Tvoid) {
         DtoStoreZextI8(ep->getRVal(), gep);

gen/tollvm.cpp

@@ -34,7 +34,7 @@
 #include "ir/irtypefunction.h"
 #include "ir/irtypestruct.h"
 
-bool DtoIsPassedByRef(Type *type) {
+bool DtoIsInMemoryOnly(Type *type) {
   Type *typ = type->toBasetype();
   TY t = typ->ty;
   return (t == Tstruct || t == Tsarray);

gen/tollvm.h

@@ -41,11 +41,13 @@ LLPointerType *DtoPtrToType(Type *t);
 LLType *voidToI8(LLType *t);
 LLType *i1ToI8(LLType *t);
 
-// returns true if the type must be passed by pointer
+// Returns true if the type is a value type which LDC keeps exclusively in
-bool DtoIsPassedByRef(Type *type);
+// memory, referencing all values via LL pointers (structs and static arrays).
+bool DtoIsInMemoryOnly(Type *type);
 
-// returns true if the return value of the call expression
+// Returns true if the callee uses sret (struct return).
-// is passed in a register
+// In that case, the caller needs to allocate the return value and pass its
+// address as additional parameter to the callee, which will set it up.
 bool DtoIsReturnInArg(CallExp *ce);
 
 // should argument be zero or sign extended