Merge pull request #7990 from WalterBright/fix18576

fix Issue 18576 - Compiler not doing RVO with auto returns
merged-on-behalf-of: Walter Bright <WalterBright@users.noreply.github.com>

src/dmd/s2ir.d

@@ -734,14 +734,26 @@ private extern (C++) class S2irVisitor : Visitor
                     sle.sym = irs.shidden;
                     writetohp = true;
                 }
-                /* Detect:
+                /* Detect function call that returns the same struct
-                 *    structliteral.ctor(args)
                  * and construct directly into *shidden
                  */
                 else if (s.exp.op == TOK.call)
                 {
                     auto ce = cast(CallExp)s.exp;
-                    if (ce.e1.op == TOK.dotVariable)
+                    if (ce.e1.op == TOK.variable || ce.e1.op == TOK.star)
+                    {
+                        Type t = ce.e1.type.toBasetype();
+                        if (t.ty == Tdelegate)
+                            t = t.nextOf();
+                        if (t.ty == Tfunction && retStyle(cast(TypeFunction)t) == RET.stack)
+                        {
+                            irs.ehidden = el_var(irs.shidden);
+                            e = toElemDtor(s.exp, irs);
+                            e = el_una(OPaddr, TYnptr, e);
+                            goto L1;
+                        }
+                    }
+                    else if (ce.e1.op == TOK.dotVariable)
                     {
                         auto dve = cast(DotVarExp)ce.e1;
                         auto fd = dve.var.isFuncDeclaration();
@@ -754,6 +766,16 @@ private extern (C++) class S2irVisitor : Visitor
                                 writetohp = true;
                             }
                         }
+                        Type t = ce.e1.type.toBasetype();
+                        if (t.ty == Tdelegate)
+                            t = t.nextOf();
+                        if (t.ty == Tfunction && retStyle(cast(TypeFunction)t) == RET.stack)
+                        {
+                            irs.ehidden = el_var(irs.shidden);
+                            e = toElemDtor(s.exp, irs);
+                            e = el_una(OPaddr, TYnptr, e);
+                            goto L1;
+                        }
                     }
                 }
                 e = toElemDtor(s.exp, irs);
@@ -787,6 +809,7 @@ private extern (C++) class S2irVisitor : Visitor
                 e = toElemDtor(s.exp, irs);
                 assert(e);
             }
+        L1:
             elem_setLoc(e, s.loc);
             block_appendexp(blx.curblock, e);
             bc = BCretexp;

test/runnable/test28.d

@@ -1,10 +1,10 @@
 module test;
 
+import core.stdc.stdio;
 import core.vararg;
 import std.stdio;
 import std.string;
 
-extern(C) int printf(const char*, ...);
 
 /*******************************************/
 
@@ -1247,6 +1247,49 @@ void test65()
 }
 
 
+/*******************************************/
+// https://issues.dlang.org/show_bug.cgi?id=18576
+
+void delegate() callback;
+
+struct S66 {
+    int x;
+    @disable this(this);
+
+    this(int x) {
+        this.x = x;
+        callback = &inc;
+    }
+    void inc() {
+        x++;
+    }
+}
+
+auto f66()
+{
+    return g66();   // RVO should be done
+}
+
+auto g66()
+{
+    return h66();   // RVO should be done
+}
+
+auto h66()
+{
+    return S66(100);
+}
+
+void test18576()
+{
+    auto s = f66();
+    printf("%p vs %p\n", &s, callback.ptr);
+    callback();
+    printf("s.x = %d\n", s.x);
+    assert(s.x == 101);
+    assert(&s == callback.ptr);
+}
+
 /*******************************************/
 
 void main()
@@ -1314,6 +1357,7 @@ void main()
     test63();
     test64();
     test65();
+    test18576();
 
     printf("Success\n");
 }