[clang] don't mark as Elidable CXXConstruct expressions used in NRVOllvmorg-13.0.0-rc4llvmorg-13.0.0

See PR51862.

The consumers of the Elidable flag in CXXConstructExpr assume that
an elidable construction just goes through a single copy/move construction,
so that the source object is immediately passed as an argument and is the same
type as the parameter itself.

With the implementation of P2266 and after some adjustments to the
implementation of P1825, we started (correctly, as per standard)
allowing more cases where the copy initialization goes through
user defined conversions.

With this patch we stop using this flag in NRVO contexts, to preserve code
that relies on that assumption.
This causes no known functional changes, we just stop firing some asserts
in a cople of included test cases.

Reviewed By: rsmith

Differential Revision: https://reviews.llvm.org/D109800

(cherry picked from commit d9308aa39b236064a680ca57178af3c731e13e49)

1 files changed, 11 insertions, 8 deletions

diff --git a/clang/lib/CodeGen/CGExprCXX.cpp b/clang/lib/CodeGen/CGExprCXX.cpp
index 96cf977ca290..f42759e9db50 100644
--- a/clang/lib/CodeGen/CGExprCXX.cpp
+++ b/clang/lib/CodeGen/CGExprCXX.cpp
@@ -609,15 +609,18 @@ CodeGenFunction::EmitCXXConstructExpr(const CXXConstructExpr *E,
     return;
 
   // Elide the constructor if we're constructing from a temporary.
-  // The temporary check is required because Sema sets this on NRVO
-  // returns.
   if (getLangOpts().ElideConstructors && E->isElidable()) {
-    assert(getContext().hasSameUnqualifiedType(E->getType(),
-                                               E->getArg(0)->getType()));
-    if (E->getArg(0)->isTemporaryObject(getContext(), CD->getParent())) {
-      EmitAggExpr(E->getArg(0), Dest);
-      return;
-    }
+    // FIXME: This only handles the simplest case, where the source object
+    //        is passed directly as the first argument to the constructor.
+    //        This should also handle stepping though implicit casts and
+    //        conversion sequences which involve two steps, with a
+    //        conversion operator followed by a converting constructor.
+    const Expr *SrcObj = E->getArg(0);
+    assert(SrcObj->isTemporaryObject(getContext(), CD->getParent()));
+    assert(
+        getContext().hasSameUnqualifiedType(E->getType(), SrcObj->getType()));
+    EmitAggExpr(SrcObj, Dest);
+    return;
   }
 
   if (const ArrayType *arrayType