[clang] [NFC][analyzer] Refactor Environment to map Expr to SVal instead of Stmt to SVal (PR #193295)

[Balázs Benics via cfe-commits]

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@@ -270,7 +270,7 @@ void MIGChecker::checkReturnAux(const ReturnStmt *RS, CheckerContext &C) const {
   if (!State->get<ReleasedParameter>())
     return;
 
-  SVal V = C.getSVal(RS);
+  SVal V = RS->getRetValue() ? C.getSVal(RS->getRetValue()) : UndefinedVal();
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steakhal wrote:

IDK what which should it be, but no reports should change. How I read this situation is that we must use `UndefinedVal` to preserve the previous behavior. That makes me wonder how did we get `UndefinedVal` previously here, but I'll leave you all explore this.

https://github.com/llvm/llvm-project/pull/193295