fix dlang#21479: Correctly handle casts inlining (dlang#21483)

Author: Albert24GG

compiler/src/dmd/e2ir.d

@@ -3852,7 +3852,8 @@ elem* toElem(Expression e, ref IRState irs)
             printf("\tfrom: %s\n", ce.e1.type.toChars());
             printf("\tto  : %s\n", ce.to.toChars());
         }
-        elem* e = toElem(ce.e1, irs);
+        // When there is a lowering availabe, use that
+        elem* e = ce.lowering is null ? toElem(ce.e1, irs) : toElem(ce.lowering, irs);
 
         return toElemCast(ce, e, false, irs);
     }
@@ -4788,7 +4789,6 @@ elem* toElemCast(CastExp ce, elem* e, bool isLvalue, ref IRState irs)
             else
             {
                 assert(ce.lowering, "This case should have been rewritten to `_d_cast` in the semantic phase");
-                e = toElem(ce.lowering, irs);
             }
         }
         return Lret(ce, e);

compiler/src/dmd/inline.d

@@ -752,21 +752,22 @@ public:
         {
             auto ue = cast(UnaExp)e.copy();
             ue.e1 = doInlineAs!Expression(e.e1, ids);
-            if (auto ce = ue.isCastExp())
-            {
-                if (ce.lowering is null)
-                    goto LskipCastLowering;
+            result = ue;
+        }
 
-                if (auto lowering = ce.lowering.isCallExp())
-                {
-                    if (lowering.f.ident == Id._d_cast)
-                    {
-                        ce.lowering = doInlineAs!Expression(lowering, ids);
-                    }
-                }
+        override void visit(CastExp e)
+        {
+            auto ce = cast(CastExp)e.copy();
+            if (auto lowering = ce.lowering)
+            {
+                ce.lowering = doInlineAs!Expression(lowering, ids);
             }
-        LskipCastLowering:
-            result = ue;
+            else
+            {
+                ce.e1 = doInlineAs!Expression(e.e1, ids);
+            }
+
+            result = ce;
         }
 
         override void visit(AssertExp e)
@@ -1291,6 +1292,18 @@ public:
         inlineScan(e.e1);
     }
 
+    override void visit(CastExp e)
+    {
+        if (auto lowering = e.lowering)
+        {
+            inlineScan(lowering);
+        }
+        else
+        {
+            inlineScan(e.e1);
+        }
+    }
+
     override void visit(AssertExp e)
     {
         inlineScan(e.e1);