Add mangling for type trait expressions.

libc++ uses type traits directly in constraints in some places, and
constraints now appear in manglings. There's a defined mangling for
these traits in the ABI already, so we should use it.

Fixes #67031.

Author: zygoloid

clang/lib/AST/ItaniumMangle.cpp

@@ -4640,7 +4640,6 @@ void CXXNameMangler::mangleExpression(const Expr *E, unsigned Arity,
   case Expr::ShuffleVectorExprClass:
   case Expr::ConvertVectorExprClass:
   case Expr::StmtExprClass:
-  case Expr::TypeTraitExprClass:
   case Expr::ArrayTypeTraitExprClass:
   case Expr::ExpressionTraitExprClass:
   case Expr::VAArgExprClass:
@@ -4992,6 +4991,10 @@ void CXXNameMangler::mangleExpression(const Expr *E, unsigned Arity,
       //   If the result of the operator is implicitly converted to a known
       //   integer type, that type is used for the literal; otherwise, the type
       //   of std::size_t or std::ptrdiff_t is used.
+      //
+      // FIXME: We still include the operand in the profile in this case. This
+      // can lead to mangling collisions between function templates that we
+      // consider to be different.
       QualType T = (ImplicitlyConvertedToType.isNull() ||
                     !ImplicitlyConvertedToType->isIntegerType())? SAE->getType()
                                                     : ImplicitlyConvertedToType;
@@ -5054,6 +5057,20 @@ void CXXNameMangler::mangleExpression(const Expr *E, unsigned Arity,
     break;
   }
 
+  case Expr::TypeTraitExprClass: {
+    //  <expression> ::= u <source-name> <template-arg>* E # vendor extension
+    const TypeTraitExpr *TTE = cast<TypeTraitExpr>(E);
+    NotPrimaryExpr();
+    Out << 'u';
+    llvm::StringRef Spelling = getTraitSpelling(TTE->getTrait());
+    Out << Spelling.size() << Spelling;
+    for (TypeSourceInfo *TSI : TTE->getArgs()) {
+      mangleType(TSI->getType());
+    }
+    Out << 'E';
+    break;
+  }
+
   case Expr::CXXThrowExprClass: {
     NotPrimaryExpr();
     const CXXThrowExpr *TE = cast<CXXThrowExpr>(E);

clang/test/CodeGenCXX/mangle-exprs.cpp

@@ -389,3 +389,13 @@ namespace null {
   // CHECK-LABEL: define {{.*}} @_ZN4null8gnu_nullILPv0EEEvPN9enable_ifIXeqT_Ll0EEvE4typeE
   template void gnu_null<nullptr>(void *);
 }
+
+namespace type_trait {
+  template<typename T> void f(decltype(__is_trivially_copyable(T))) {}
+  // CHECK-LABEL: define {{.*}} @_ZN10type_trait1fIiEEvDTu23__is_trivially_copyableT_EE
+  template void f<int>(bool);
+
+  template<typename T> void g(decltype(__is_trivially_copyable(int) + T())) {}
+  // CHECK-LABEL: define {{.*}} @_ZN10type_trait1gIiEEvDTplu23__is_trivially_copyableiEcvT__EE
+  template void g<int>(int);
+}