[Clang] Fix nesting of discarded and immediate contexts.

In C++23, discarded statements and if consteval statements can nest
arbitrarily. To support that, we keep track of whether the parent of
the current evaluation context is discarded or immediate.

This is done at the construction of an evaluation context
to improve performance.

Fixes https://bugs.llvm.org/show_bug.cgi?id=52231

diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index c969d97..1a82a94 100644 (file)
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -1296,6 +1296,11 @@ public:
       EK_Decltype, EK_TemplateArgument, EK_Other
     } ExprContext;
 
+    // A context can be nested in both a discarded statement context and
+    // an immediate function context, so they need to be tracked independently.
+    bool InDiscardedStatement;
+    bool InImmediateFunctionContext;
+
     ExpressionEvaluationContextRecord(ExpressionEvaluationContext Context,
                                       unsigned NumCleanupObjects,
                                       CleanupInfo ParentCleanup,
@@ -1303,7 +1308,8 @@ public:
                                       ExpressionKind ExprContext)
         : Context(Context), ParentCleanup(ParentCleanup),
           NumCleanupObjects(NumCleanupObjects), NumTypos(0),
-          ManglingContextDecl(ManglingContextDecl), ExprContext(ExprContext) {}
+          ManglingContextDecl(ManglingContextDecl), ExprContext(ExprContext),
+          InDiscardedStatement(false), InImmediateFunctionContext(false) {}
 
     bool isUnevaluated() const {
       return Context == ExpressionEvaluationContext::Unevaluated ||
@@ -1317,7 +1323,13 @@ public:
     }
 
     bool isImmediateFunctionContext() const {
-      return Context == ExpressionEvaluationContext::ImmediateFunctionContext;
+      return Context == ExpressionEvaluationContext::ImmediateFunctionContext ||
+             InImmediateFunctionContext;
+    }
+
+    bool isDiscardedStatementContext() const {
+      return Context == ExpressionEvaluationContext::DiscardedStatement ||
+             InDiscardedStatement;
     }
   };
 
@@ -9154,14 +9166,7 @@ public:
   bool isImmediateFunctionContext() const {
     assert(!ExprEvalContexts.empty() &&
            "Must be in an expression evaluation context");
-    for (const ExpressionEvaluationContextRecord &context :
-         llvm::reverse(ExprEvalContexts)) {
-      if (context.isImmediateFunctionContext())
-        return true;
-      if (context.isUnevaluated())
-        return false;
-    }
-    return false;
+    return ExprEvalContexts.back().isImmediateFunctionContext();
   }
 
   /// RAII class used to determine whether SFINAE has

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 8592335..b305d4e 100644 (file)
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -16566,6 +16566,17 @@ Sema::PushExpressionEvaluationContext(
     ExpressionEvaluationContextRecord::ExpressionKind ExprContext) {
   ExprEvalContexts.emplace_back(NewContext, ExprCleanupObjects.size(), Cleanup,
                                 LambdaContextDecl, ExprContext);
+
+  // Discarded statements and immediate contexts nested in other
+  // discarded statements or immediate context are themselves
+  // a discarded statement or an immediate context, respectively.
+  ExprEvalContexts.back().InDiscardedStatement =
+      ExprEvalContexts[ExprEvalContexts.size() - 2]
+          .isDiscardedStatementContext();
+  ExprEvalContexts.back().InImmediateFunctionContext =
+      ExprEvalContexts[ExprEvalContexts.size() - 2]
+          .isImmediateFunctionContext();
+
   Cleanup.reset();
   if (!MaybeODRUseExprs.empty())
     std::swap(MaybeODRUseExprs, ExprEvalContexts.back().SavedMaybeODRUseExprs);
@@ -18965,6 +18976,10 @@ bool Sema::DiagIfReachable(SourceLocation Loc, ArrayRef<const Stmt *> Stmts,
 /// during overload resolution or within sizeof/alignof/typeof/typeid.
 bool Sema::DiagRuntimeBehavior(SourceLocation Loc, ArrayRef<const Stmt*> Stmts,
                                const PartialDiagnostic &PD) {
+
+  if (ExprEvalContexts.back().isDiscardedStatementContext())
+    return false;
+
   switch (ExprEvalContexts.back().Context) {
   case ExpressionEvaluationContext::Unevaluated:
   case ExpressionEvaluationContext::UnevaluatedList:

diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index 3c82082..1d90759 100644 (file)
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -3563,8 +3563,7 @@ StmtResult Sema::ActOnCapScopeReturnStmt(SourceLocation ReturnLoc,
   bool HasDeducedReturnType =
       CurLambda && hasDeducedReturnType(CurLambda->CallOperator);
 
-  if (ExprEvalContexts.back().Context ==
-          ExpressionEvaluationContext::DiscardedStatement &&
+  if (ExprEvalContexts.back().isDiscardedStatementContext() &&
       (HasDeducedReturnType || CurCap->HasImplicitReturnType)) {
     if (RetValExp) {
       ExprResult ER =
@@ -3880,8 +3879,7 @@ Sema::ActOnReturnStmt(SourceLocation ReturnLoc, Expr *RetValExp,
   if (RetVal.isInvalid())
     return StmtError();
   StmtResult R = BuildReturnStmt(ReturnLoc, RetVal.get());
-  if (R.isInvalid() || ExprEvalContexts.back().Context ==
-                           ExpressionEvaluationContext::DiscardedStatement)
+  if (R.isInvalid() || ExprEvalContexts.back().isDiscardedStatementContext())
     return R;
 
   if (VarDecl *VD =
@@ -3966,8 +3964,7 @@ StmtResult Sema::BuildReturnStmt(SourceLocation ReturnLoc, Expr *RetValExp) {
 
   // C++1z: discarded return statements are not considered when deducing a
   // return type.
-  if (ExprEvalContexts.back().Context ==
-          ExpressionEvaluationContext::DiscardedStatement &&
+  if (ExprEvalContexts.back().isDiscardedStatementContext() &&
       FnRetType->getContainedAutoType()) {
     if (RetValExp) {
       ExprResult ER =

diff --git a/clang/test/SemaCXX/cxx2b-consteval-if.cpp b/clang/test/SemaCXX/cxx2b-consteval-if.cpp
index e60959e..ca65f27 100644 (file)
--- a/clang/test/SemaCXX/cxx2b-consteval-if.cpp
+++ b/clang/test/SemaCXX/cxx2b-consteval-if.cpp
@@ -52,6 +52,5 @@ auto f() {
       return 0;
     }
   }
-  // FIXME: this error should not happen.
-  return 0.0; // expected-error {{'auto' in return type deduced as 'double' here but deduced as 'int' in earlier return statement}}
+  return 0.0;
 }