[PATCH] D119646: [clang] Allow consteval functions in default arguments

[Evgeny Shulgin via Phabricator via cfe-commits]

Izaron created this revision.
Izaron added reviewers: aaron.ballman, erichkeane, andreasfertig.
Herald added a subscriber: kristof.beyls.
Izaron requested review of this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

We should not mark a function as "referenced" if we call it within a
ConstantExpr, because the expression will be folded to a value in LLVM IR.
To prevent emitting consteval function declarations, we should not "jump over"
a ConstantExpr when it is a top-level ParmVarDecl's subexpression.

Fixes https://github.com/llvm/llvm-project/issues/48230


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D119646

Files:
  clang/lib/AST/Decl.cpp
  clang/lib/Sema/SemaExpr.cpp
  clang/test/SemaCXX/cxx2a-consteval.cpp


Index: clang/test/SemaCXX/cxx2a-consteval.cpp
===================================================================
--- clang/test/SemaCXX/cxx2a-consteval.cpp
+++ clang/test/SemaCXX/cxx2a-consteval.cpp
@@ -613,6 +613,27 @@
 
 } // namespace unevaluated
 
+namespace default_argument {
+
+// Previously calls of consteval functions in default arguments were rejected.
+// Now we show that we don't reject such calls.
+consteval int foo() { return 1; }
+consteval int bar(int i = foo()) { return i * i; }
+
+struct Test1 {
+  Test1(int i = bar(13)) {}
+  void v(int i = bar(13) * 2 + bar(15)) {}
+};
+Test1 t1;
+
+struct Test2 {
+  constexpr Test2(int i = bar()) {}
+  constexpr void v(int i = bar(bar(bar(foo())))) {}
+};
+Test2 t2;
+
+} // namespace default_argument
+
 namespace PR50779 {
 struct derp {
   int b = 0;
Index: clang/lib/Sema/SemaExpr.cpp
===================================================================
--- clang/lib/Sema/SemaExpr.cpp
+++ clang/lib/Sema/SemaExpr.cpp
@@ -18964,6 +18964,12 @@
     Inherited::Visit(E);
   }
 
+  void VisitConstantExpr(ConstantExpr *E) {
+    // Don't mark declarations within a ConstantExpression, as this expression
+    // will be evaluated and folded to a value.
+    return;
+  }
+
   void VisitDeclRefExpr(DeclRefExpr *E) {
     // If we were asked not to visit local variables, don't.
     if (SkipLocalVariables) {
Index: clang/lib/AST/Decl.cpp
===================================================================
--- clang/lib/AST/Decl.cpp
+++ clang/lib/AST/Decl.cpp
@@ -2813,7 +2813,8 @@
 
   Expr *Arg = getInit();
   if (auto *E = dyn_cast_or_null<FullExpr>(Arg))
-    return E->getSubExpr();
+    if (!isa<ConstantExpr>(E))
+      return E->getSubExpr();
 
   return Arg;
 }


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