Reapply r183721, reverted in r183776, with a fix for a bug in the former (we

were lacking ExprWithCleanups nodes in some cases where the new approach to
lifetime extension needed them).

Original commit message:

Rework IR emission for lifetime-extended temporaries. Instead of trying to walk
into the expression and dig out a single lifetime-extended entity and manually
pull its cleanup outside the expression, instead keep a list of the cleanups
which we'll need to emit when we get to the end of the full-expression. Also
emit those cleanups early, as EH-only cleanups, to cover the case that the
full-expression does not terminate normally. This allows IR generation to
properly model temporary lifetime when multiple temporaries are extended by the
same declaration.

We have a pre-existing bug where an exception thrown from a temporary's
destructor does not clean up lifetime-extended temporaries created in the same
expression and extended to automatic storage duration; that is not fixed by
this patch.

llvm-svn: 183859

clang/lib/CodeGen/CodeGenFunction.cpp

@@ -65,6 +65,8 @@ CodeGenFunction::CodeGenFunction(CodeGenModule &cgm, bool suppressNewContext)
 }
 
 CodeGenFunction::~CodeGenFunction() {
+  assert(LifetimeExtendedCleanupStack.empty() && "failed to emit a cleanup");
+
   // If there are any unclaimed block infos, go ahead and destroy them
   // now.  This can happen if IR-gen gets clever and skips evaluating
   // something.