[PATCH] D36876: [IRGen] Evaluate constant static variables referenced through member expressions

[Alex Lorenz via Phabricator via cfe-commits]

arphaman added inline comments.


================
Comment at: lib/CodeGen/CGExpr.cpp:1323
+  if (result.HasSideEffects && !AllowSideEffects) {
+    assert(!isa<DeclRefExpr>(E) && "declrefs should not have side effects");
     return ConstantEmission();
----------------
rjmccall wrote:
> The side effects here are those associated with the initializer of the referenced declaration, not the DRE itself.  Some expressions can be constant-evaluated despite having side-effects because the side-effects occur in an ignored operand, like the LHS of a comma or the base of a MemberExpr that refers to a static member.
> 
> We can't allow side effects here because (1) we're not actually collecting the side-effectful expressions to emit and (2) we'd need some permission from the context to decide that we're allowed to do so anyway (with a lambda capture, those side-effects have actually already been emitted, but I'm not convinced that's always true).
> 
> On the other hand, I think we need to be able to emit MemberExprs to static members as constants despite the presence of side-effects in their base expressions, and I can't think of any reasonable way to do that except actually making a temporary DeclRefExpr to try to constant-emit instead.
Thanks, I think I understand your explanation.

I will try using temporary a DRE instead when a static variable is used in a member expression. That means that the old integer field evaluation code will have to stay though.


Repository:
  rL LLVM

https://reviews.llvm.org/D36876