[clang] 6eeda06 - [Clang] Fix nesting of discarded and immediate contexts.

[Aaron Ballman via cfe-commits]

Author: Corentin Jabot
Date: 2021-12-01T12:58:32-05:00
New Revision: 6eeda06c1d22da2b9fe96a2569a8a0f8e4f36880

URL: https://github.com/llvm/llvm-project/commit/6eeda06c1d22da2b9fe96a2569a8a0f8e4f36880
DIFF: https://github.com/llvm/llvm-project/commit/6eeda06c1d22da2b9fe96a2569a8a0f8e4f36880.diff

LOG: [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

Added: 
    

Modified: 
    clang/include/clang/Sema/Sema.h
    clang/lib/Sema/SemaExpr.cpp
    clang/lib/Sema/SemaStmt.cpp
    clang/test/SemaCXX/cxx2b-consteval-if.cpp

Removed: 
    


################################################################################
diff  --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index c969d97baccce..1a82a9498d1d3 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -1296,6 +1296,11 @@ class Sema final {
       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 @@ class Sema final {
                                       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 @@ class Sema final {
     }
 
     bool isImmediateFunctionContext() const {
-      return Context == ExpressionEvaluationContext::ImmediateFunctionContext;
+      return Context == ExpressionEvaluationContext::ImmediateFunctionContext ||
+             InImmediateFunctionContext;
+    }
+
+    bool isDiscardedStatementContext() const {
+      return Context == ExpressionEvaluationContext::DiscardedStatement ||
+             InDiscardedStatement;
     }
   };
 
@@ -9154,14 +9166,7 @@ class Sema final {
   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 8592335e20d31..b305d4e5b92f5 100644
--- 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 3c820829864d0..1d90759f24069 100644
--- 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 e60959e5988d0..ca65f2733fc1d 100644
--- 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;
 }