[clang] a053929 - [AST] Fix a constexpr-evaluator crash on error-dependent returnstmt.

[Haojian Wu via cfe-commits]

Author: Haojian Wu
Date: 2020-12-10T10:12:15+01:00
New Revision: a0539298540e49cb734c7b82f93572ab46bf9b00

URL: https://github.com/llvm/llvm-project/commit/a0539298540e49cb734c7b82f93572ab46bf9b00
DIFF: https://github.com/llvm/llvm-project/commit/a0539298540e49cb734c7b82f93572ab46bf9b00.diff

LOG: [AST] Fix a constexpr-evaluator crash on error-dependent returnstmt.

When the evaluator encounters an error-dependent returnstmt, before this patch
it returned a ESR_Returned without setting the result, the callsides think this
is a successful execution, and try to access the Result which causes the crash.

The fix is to always return failed as we don't know the result of the
error-dependent return stmt.

Differential Revision: https://reviews.llvm.org/D92969

Added: 
    

Modified: 
    clang/lib/AST/ExprConstant.cpp
    clang/test/SemaCXX/constexpr-function-recovery-crash.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index fc1d2cd7757e..0865b8b85138 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -5142,8 +5142,11 @@ static EvalStmtResult EvaluateStmt(StmtResult &Result, EvalInfo &Info,
   case Stmt::ReturnStmtClass: {
     const Expr *RetExpr = cast<ReturnStmt>(S)->getRetValue();
     FullExpressionRAII Scope(Info);
-    if (RetExpr && RetExpr->isValueDependent())
-      return EvaluateDependentExpr(RetExpr, Info) ? ESR_Returned : ESR_Failed;
+    if (RetExpr && RetExpr->isValueDependent()) {
+      EvaluateDependentExpr(RetExpr, Info);
+      // We know we returned, but we don't know what the value is.
+      return ESR_Failed;
+    }
     if (RetExpr &&
         !(Result.Slot
               ? EvaluateInPlace(Result.Value, Info, *Result.Slot, RetExpr)

diff  --git a/clang/test/SemaCXX/constexpr-function-recovery-crash.cpp b/clang/test/SemaCXX/constexpr-function-recovery-crash.cpp
index 48a0d97619e4..94be9a12bc66 100644
--- a/clang/test/SemaCXX/constexpr-function-recovery-crash.cpp
+++ b/clang/test/SemaCXX/constexpr-function-recovery-crash.cpp
@@ -66,3 +66,6 @@ template<int x> constexpr int f(int y) { // expected-note {{candidate template i
 constexpr int test9(int x) {
   return f<1>(f<x>(1)); // expected-error {{no matching function for call to 'f'}}
 }
+
+constexpr int test10() { return undef(); } // expected-error {{use of undeclared identifier 'undef'}}
+static_assert(test10() <= 1, "should not crash"); // expected-error {{static_assert expression is not an integral constant expression}}