[PATCH] D84637: [AST] Enhance the const expression evaluator to support error-dependent exprs.

[Haojian Wu via Phabricator via cfe-commits]

hokein marked an inline comment as done.
hokein added inline comments.


================
Comment at: clang/lib/AST/ExprConstant.cpp:4961
     }
+    if (IS->getCond()->isValueDependent())
+      return EvaluateDependentExpr(IS->getCond(), Info);
----------------
The `if` stmt (the same to `while`, `for`) is tricky -- if the condition is value-dependent, then we don't know which branch we should run into.

- returning a ESR_Succeeded may lead to a bogus diagnostic ("reach the end of the function");
- returning a ESR_Failed may lead to a bogus diagnostic ("never produce a constexpr"); 

I guess what we want is to stop the evaluation, and indicate that we hit a value-dependent expression and we don't know how to evaluate it, but still treat the constexpr function as potential constexpr (but no extra diagnostics being emitted), but the current `EvalStmtResult` is not sufficient, maybe we need a new enum.


Repository:
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  https://reviews.llvm.org/D84637/new/

https://reviews.llvm.org/D84637