add Placement New

changelog/dmd.placementNew.dd

@@ -0,0 +1,20 @@
+# Added Placement New Expression
+
+Placement new explicitly provides the storage for NewExpression to initialize
+with the newly created value, rather than using the GC.
+
+---
+struct S
+{
+    float d;
+    int i;
+    char c;
+}
+
+void main()
+{
+    S s;
+    S* p = new (s) S(); // place new object into s
+    assert(p.i == 0 && p.c == 0xFF);
+}
+---

compiler/src/dmd/astbase.d

@@ -4814,10 +4814,12 @@
         Expression thisexp;     // if !=null, 'this' for class being allocated
         ClassDeclaration cd;    // class being instantiated
         Expressions* arguments; // Array of Expression's to call class constructor
+        Expression placement;   // if != null, then PlacementExpression
 
-        extern (D) this(const ref Loc loc, Expression thisexp, ClassDeclaration cd, Expressions* arguments)
+        extern (D) this(const ref Loc loc, Expression placement, Expression thisexp, ClassDeclaration cd, Expressions* arguments)
         {
             super(loc, EXP.newAnonymousClass, __traits(classInstanceSize, NewAnonClassExp));
+            this.placement = placement;
             this.thisexp = thisexp;
             this.cd = cd;
             this.arguments = arguments;
@@ -5026,10 +5028,12 @@
         Type newtype;
         Expressions* arguments;     // Array of Expression's
         Identifiers* names;         // Array of names corresponding to expressions
+        Expression placement;       // if != null, then PlacementExpression
 
-        extern (D) this(const ref Loc loc, Expression thisexp, Type newtype, Expressions* arguments, Identifiers* names = null)
+        extern (D) this(const ref Loc loc, Expression placement, Expression thisexp, Type newtype, Expressions* arguments, Identifiers* names = null)
         {
             super(loc, EXP.new_, __traits(classInstanceSize, NewExp));
+            this.placement = placement;
             this.thisexp = thisexp;
             this.newtype = newtype;
             this.arguments = arguments;

compiler/src/dmd/dinterpret.d

@@ -2794,6 +2794,13 @@
             printf("%s NewExp::interpret() %s\n", e.loc.toChars(), e.toChars());
         }
 
+        if (e.placement)
+        {
+            error(e.placement.loc, "`new ( %s )` PlacementExpression cannot be evaluated at compile time", e.placement.toChars());
+            result = CTFEExp.cantexp;
+            return;
+        }
+
         Expression epre = interpret(pue, e.argprefix, istate, CTFEGoal.Nothing);
         if (exceptionOrCant(epre))
             return;
@@ -5040,7 +5047,7 @@
             auto ce = e.e2.isCallExp();
             assert(ce);
 
-            auto ne = new NewExp(e.loc, null, e.type, ce.arguments);
+            auto ne = new NewExp(e.loc, null, null, e.type, ce.arguments);
             ne.type = e.e1.type;
 
             result = interpret(ne, istate);

compiler/src/dmd/dsymbolsem.d

@@ -1312,9 +1312,12 @@ private extern(C++) final class DsymbolSemanticVisitor : Visitor
                             ex = (cast(AssignExp)ex).e2;
                         if (auto ne = ex.isNewExp())
                         {
+                            if (ne.placement)
+                            {
+                            }
                             /* See if initializer is a NewExp that can be allocated on the stack.
                              */
-                            if (dsym.type.toBasetype().ty == Tclass)
+                            else if (dsym.type.toBasetype().ty == Tclass)
                             {
                                 /* Unsafe to allocate on stack if constructor is not `scope` because the `this` can leak.
                                  * https://issues.dlang.org/show_bug.cgi?id=23145

compiler/src/dmd/dtemplate.d

@@ -3008,6 +3008,8 @@
         override void visit(NewExp e)
         {
             //printf("NewExp.reliesOnTemplateParameters('%s')\n", e.toChars());
+            if (e.placement)
+                e.placement.accept(this);
             if (e.thisexp)
                 e.thisexp.accept(this);
             result = e.newtype.reliesOnTemplateParameters(tparams);

compiler/src/dmd/e2ir.d

@@ -1126,19 +1126,27 @@
             elem *ezprefix = null;
             elem *ez = null;
 
-            if (ne.onstack)
+            if (ne.onstack || ne.placement)
             {
-                /* Create an instance of the class on the stack,
-                 * and call it stmp.
-                 * Set ex to be the &stmp.
-                 */
-                .type *tc = type_struct_class(tclass.sym.toChars(),
-                        tclass.sym.alignsize, tclass.sym.structsize,
-                        null, null,
-                        false, false, true, false);
-                tc.Tcount--;
-                Symbol *stmp = symbol_genauto(tc);
-                ex = el_ptr(stmp);
+                if (ne.placement)
+                {
+                    ex = toElem(ne.placement, irs);
+                    ex = addressElem(ex, ne.newtype.toBasetype(), false);
+                }
+                else
+                {
+                    /* Create an instance of the class on the stack,
+                     * and call it stmp.
+                     * Set ex to be the &stmp.
+                     */
+                    .type *tc = type_struct_class(tclass.sym.toChars(),
+                            tclass.sym.alignsize, tclass.sym.structsize,
+                            null, null,
+                            false, false, true, false);
+                    tc.Tcount--;
+                    Symbol *stmp = symbol_genauto(tc);
+                    ex = el_ptr(stmp);
+                }
 
                 Symbol *si = toInitializer(tclass.sym);
                 elem *ei = el_var(si);
@@ -1265,8 +1273,13 @@
             elem *ezprefix = null;
             elem *ez = null;
 
-            // Call _d_newitemT()
-            if (auto lowering = ne.lowering)
+            if (ne.placement)
+            {
+                ex = toElem(ne.placement, irs);
+                ex = addressElem(ex, tclass, false);
+            }
+            else if (auto lowering = ne.lowering)
+                // Call _d_newitemT()
                 ex = toElem(ne.lowering, irs);
             else
                 assert(0, "This case should have been rewritten to `_d_newitemT` in the semantic phase");
@@ -1276,7 +1289,7 @@
             elem *ev = el_same(ex);
 
             if (ne.argprefix)
-                    ezprefix = toElem(ne.argprefix, irs);
+                ezprefix = toElem(ne.argprefix, irs);
             if (ne.member)
             {
                 if (sd.isNested())
@@ -1308,10 +1321,12 @@
             {
                 StructLiteralExp sle = StructLiteralExp.create(ne.loc, sd, ne.arguments, t);
                 ez = toElemStructLit(sle, irs, EXP.construct, ev.Vsym, false);
+                if (tybasic(ez.Ety) == TYstruct)
+                    ez = el_una(OPaddr, TYnptr, ez);
             }
             //elem_print(ex);
             //elem_print(ey);
-            //elem_print(ez);
+            //printf("ez:\n"); elem_print(ez);
 
             e = el_combine(ex, ey);
             e = el_combine(e, ew);
@@ -1331,8 +1346,16 @@
         {
             elem *ezprefix = ne.argprefix ? toElem(ne.argprefix, irs) : null;
 
-            // call _d_newitemT()
-            e = toElem(ne.lowering, irs);
+            if (ne.placement)
+            {
+                e = toElem(ne.placement, irs);
+                e = addressElem(e, ne.newtype.toBasetype(), false);
+            }
+            else if (auto lowering = ne.lowering)
+                // Call _d_newitemT()
+                e = toElem(ne.lowering, irs);
+            else
+                assert(0, "This case should have been rewritten to `_d_newitemT` in the semantic phase");
 
             if (ne.arguments && ne.arguments.length == 1)
             {

compiler/src/dmd/escape.d

@@ -1637,6 +1637,9 @@ void escapeExp(Expression e, ref scope EscapeByResults er, int deref)
 
     void visitNew(NewExp e)
     {
+        if (e.placement)
+            escapeExp(e.placement, er, deref);
+
         Type tb = e.newtype.toBasetype();
         if (tb.isTypeStruct() && !e.member && e.arguments)
         {

compiler/src/dmd/expression.d

@@ -2560,6 +2560,7 @@
     Type newtype;
     Expressions* arguments;     // Array of Expression's
     Identifiers* names;         // Array of names corresponding to expressions
+    Expression placement;       // if !=null, then PlacementExpression
 
     Expression argprefix;       // expression to be evaluated just before arguments[]
     CtorDeclaration member;     // constructor function
@@ -2572,23 +2573,25 @@
     /// The fields are still separate for backwards compatibility
     extern (D) ArgumentList argumentList() { return ArgumentList(arguments, names); }
 
-    extern (D) this(const ref Loc loc, Expression thisexp, Type newtype, Expressions* arguments, Identifiers* names = null) @safe
+    extern (D) this(const ref Loc loc, Expression placement, Expression thisexp, Type newtype, Expressions* arguments, Identifiers* names = null) @safe
     {
         super(loc, EXP.new_);
+        this.placement = placement;
         this.thisexp = thisexp;
         this.newtype = newtype;
         this.arguments = arguments;
         this.names = names;
     }
 
-    static NewExp create(const ref Loc loc, Expression thisexp, Type newtype, Expressions* arguments) @safe
+    static NewExp create(const ref Loc loc, Expression placement, Expression thisexp, Type newtype, Expressions* arguments) @safe
     {
-        return new NewExp(loc, thisexp, newtype, arguments);
+        return new NewExp(loc, placement, thisexp, newtype, arguments);
     }
 
     override NewExp syntaxCopy()
     {
         return new NewExp(loc,
+            placement ? placement.syntaxCopy() : null,
             thisexp ? thisexp.syntaxCopy() : null,
             newtype.syntaxCopy(),
             arraySyntaxCopy(arguments),
@@ -2609,18 +2612,22 @@
     Expression thisexp;     // if !=null, 'this' for class being allocated
     ClassDeclaration cd;    // class being instantiated
     Expressions* arguments; // Array of Expression's to call class constructor
+    Expression placement;   // if !=null, then PlacementExpression
 
-    extern (D) this(const ref Loc loc, Expression thisexp, ClassDeclaration cd, Expressions* arguments) @safe
+    extern (D) this(const ref Loc loc, Expression placement, Expression thisexp, ClassDeclaration cd, Expressions* arguments) @safe
     {
         super(loc, EXP.newAnonymousClass);
+        this.placement = placement;
         this.thisexp = thisexp;
         this.cd = cd;
         this.arguments = arguments;
     }
 
     override NewAnonClassExp syntaxCopy()
     {
-        return new NewAnonClassExp(loc, thisexp ? thisexp.syntaxCopy() : null, cd.syntaxCopy(null), arraySyntaxCopy(arguments));
+        return new NewAnonClassExp(loc, placement ? placement.syntaxCopy : null,
+                                        thisexp ? thisexp.syntaxCopy() : null,
+                                        cd.syntaxCopy(null), arraySyntaxCopy(arguments));
     }
 
     override void accept(Visitor v)

compiler/src/dmd/expression.h

@@ -510,6 +510,7 @@ class NewExp final : public Expression
     Type *newtype;
     Expressions *arguments;     // Array of Expression's
     Identifiers *names;         // Array of names corresponding to expressions
+    Expression *placement;      // if !NULL, placement expression
 
     Expression *argprefix;      // expression to be evaluated just before arguments[]
 
@@ -519,7 +520,7 @@ class NewExp final : public Expression
 
     Expression *lowering;       // lowered druntime hook: `_d_newclass`
 
-    static NewExp *create(const Loc &loc, Expression *thisexp, Type *newtype, Expressions *arguments);
+    static NewExp *create(const Loc &loc, Expression *placement, Expression *thisexp, Type *newtype, Expressions *arguments);
     NewExp *syntaxCopy() override;
 
     void accept(Visitor *v) override { v->visit(this); }
@@ -533,6 +534,7 @@ class NewAnonClassExp final : public Expression
     Expression *thisexp;        // if !NULL, 'this' for class being allocated
     ClassDeclaration *cd;       // class being instantiated
     Expressions *arguments;     // Array of Expression's to call class constructor
+    Expression *placement;      // if !NULL, placement expression
 
     NewAnonClassExp *syntaxCopy() override;
     void accept(Visitor *v) override { v->visit(this); }