[PATCH] D106302: Implement P1937 consteval in unevaluated contexts

[Corentin Jabot via Phabricator via cfe-commits]

cor3ntin created this revision.
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In an unevaluated contexts, consteval functions
should not be immediately evaluated.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D106302

Files:
  clang/lib/Sema/SemaExpr.cpp
  clang/test/SemaCXX/cxx2a-consteval.cpp
  clang/www/cxx_status.html


Index: clang/www/cxx_status.html
===================================================================
--- clang/www/cxx_status.html
+++ clang/www/cxx_status.html
@@ -1103,10 +1103,11 @@
     <tr>
       <td rowspan=2>Immediate functions (<tt>consteval</tt>)</td>
       <td><a href="https://wg21.link/p1073r3">P1073R3</a></td>
-      <td rowspan=2 class="none" align="center">No</td>
+      <td class="partial" align="center">Partial</td>
     </tr>
       <tr> <!-- from Prague -->
         <td><a href="https://wg21.link/p1937r2">P1937R2</a></td>
+        <td class="unreleased" align="center">Clang 13</td>
       </tr>
     <tr>
       <td><tt>std::is_constant_evaluated</tt></td>
Index: clang/test/SemaCXX/cxx2a-consteval.cpp
===================================================================
--- clang/test/SemaCXX/cxx2a-consteval.cpp
+++ clang/test/SemaCXX/cxx2a-consteval.cpp
@@ -594,3 +594,20 @@
 }
 
 } // namespace special_ctor
+
+namespace unevaluated {
+
+template <typename T, typename U> struct is_same { static const bool value = false; };
+template <typename T> struct is_same<T, T> { static const bool value = true; };
+
+long f(); //expected-note {{declared here}}
+auto consteval g(auto a) {
+  return a;
+}
+
+auto e = g(f()); // expected-error{{is not a constant expression}} expected-note {{non-constexpr function 'f' cannot be used in a constant expression}}
+
+using T = decltype(g(f()));
+static_assert(is_same<long, T>::value);
+
+} // namespace unevaluated
Index: clang/lib/Sema/SemaExpr.cpp
===================================================================
--- clang/lib/Sema/SemaExpr.cpp
+++ clang/lib/Sema/SemaExpr.cpp
@@ -16585,7 +16585,8 @@
 }
 
 ExprResult Sema::CheckForImmediateInvocation(ExprResult E, FunctionDecl *Decl) {
-  if (!E.isUsable() || !Decl || !Decl->isConsteval() || isConstantEvaluated() ||
+  if (isUnevaluatedContext() || !E.isUsable() || !Decl ||
+      !Decl->isConsteval() || isConstantEvaluated() ||
       RebuildingImmediateInvocation)
     return E;
 
@@ -18702,8 +18703,8 @@
       OdrUse = false;
 
   if (auto *FD = dyn_cast<FunctionDecl>(E->getDecl()))
-    if (!isConstantEvaluated() && FD->isConsteval() &&
-        !RebuildingImmediateInvocation)
+    if (!isUnevaluatedContext() && !isConstantEvaluated() &&
+        FD->isConsteval() && !RebuildingImmediateInvocation)
       ExprEvalContexts.back().ReferenceToConsteval.insert(E);
   MarkExprReferenced(*this, E->getLocation(), E->getDecl(), E, OdrUse,
                      RefsMinusAssignments);


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