[clang] [clang][ExprConst] Don't try to evaluate value-dependent DeclRefExprs (PR #67778)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/67778

The Expression here migth be value dependent, which makes us run into an assertion later on. Just bail out early.

Fixes #67690

>From c696a6e15404235cf9cab8fc69a39e828d5da03e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Fri, 29 Sep 2023 11:23:55 +0200
Subject: [PATCH] [clang][ExprConst] Don't try to evaluate value-dependent
 DeclRefExprs

The Expression here migth be value dependent, which makes us run into an
assertion later on. Just bail out early.

Fixes #67690
---
 clang/lib/AST/ExprConstant.cpp                   |  3 +++
 clang/test/SemaCXX/constant-expression-cxx1z.cpp | 13 +++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index fea06b97259fe31..8372d81234669fd 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -3357,6 +3357,9 @@ static bool evaluateVarDeclInit(EvalInfo &Info, const Expr *E,
     return false;
   }
 
+  if (E->isValueDependent())
+    return false;
+
   // Dig out the initializer, and use the declaration which it's attached to.
   // FIXME: We should eventually check whether the variable has a reachable
   // initializing declaration.
diff --git a/clang/test/SemaCXX/constant-expression-cxx1z.cpp b/clang/test/SemaCXX/constant-expression-cxx1z.cpp
index 9335626a5c90a4f..a36b8f15f826f41 100644
--- a/clang/test/SemaCXX/constant-expression-cxx1z.cpp
+++ b/clang/test/SemaCXX/constant-expression-cxx1z.cpp
@@ -177,3 +177,16 @@ namespace LambdaCallOp {
     p();
   }
 }
+
+/// This used to crash due to an assertion failure,
+/// see gh#67690
+namespace {
+  struct C {
+    int x;
+  };
+
+  template <const C *p> void f() {
+    const auto &[c] = *p;
+    &c;
+  }
+}