P0426: Make the library implementation of constexpr char_traits a little easier

by providing a memchr builtin that returns char* instead of void*.

Also add a __has_feature flag to indicate the presence of constexpr forms of
the relevant <string> functions.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@292555 91177308-0d34-0410-b5e6-96231b3b80d8

Author: zygoloid

include/clang/Basic/Builtins.def

@@ -1339,6 +1339,7 @@ BUILTIN(__builtin_smulll_overflow, "bSLLiCSLLiCSLLi*", "n")
 BUILTIN(__builtin_addressof, "v*v&", "nct")
 BUILTIN(__builtin_operator_new, "v*z", "c")
 BUILTIN(__builtin_operator_delete, "vv*", "n")
+BUILTIN(__builtin_char_memchr, "c*cC*iz", "n")
 
 // Safestack builtins
 BUILTIN(__builtin___get_unsafe_stack_start, "v*", "Fn")

lib/AST/ExprConstant.cpp

@@ -5683,6 +5683,7 @@ bool PointerExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
   case Builtin::BI__builtin_strchr:
   case Builtin::BI__builtin_wcschr:
   case Builtin::BI__builtin_memchr:
+  case Builtin::BI__builtin_char_memchr:
   case Builtin::BI__builtin_wmemchr: {
     if (!Visit(E->getArg(0)))
       return false;
@@ -5720,6 +5721,7 @@ bool PointerExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
       // Fall through.
     case Builtin::BImemchr:
     case Builtin::BI__builtin_memchr:
+    case Builtin::BI__builtin_char_memchr:
       // memchr compares by converting both sides to unsigned char. That's also
       // correct for strchr if we get this far (to cope with plain char being
       // unsigned in the strchr case).

lib/CodeGen/CGBuiltin.cpp

@@ -1189,6 +1189,10 @@ RValue CodeGenFunction::EmitBuiltinExpr(const FunctionDecl *FD,
     return RValue::get(Dest.getPointer());
   }
 
+  case Builtin::BI__builtin_char_memchr:
+    BuiltinID = Builtin::BI__builtin_memchr;
+    break;
+
   case Builtin::BI__builtin___memcpy_chk: {
     // fold __builtin_memcpy_chk(x, y, cst1, cst2) to memcpy iff cst1<=cst2.
     llvm::APSInt Size, DstSize;

lib/Lex/PPMacroExpansion.cpp

@@ -1183,6 +1183,7 @@ static bool HasFeature(const Preprocessor &PP, StringRef Feature) {
       .Case("cxx_attributes", LangOpts.CPlusPlus11)
       .Case("cxx_auto_type", LangOpts.CPlusPlus11)
       .Case("cxx_constexpr", LangOpts.CPlusPlus11)
+      .Case("cxx_constexpr_string_builtins", LangOpts.CPlusPlus11)
       .Case("cxx_decltype", LangOpts.CPlusPlus11)
       .Case("cxx_decltype_incomplete_return_types", LangOpts.CPlusPlus11)
       .Case("cxx_default_function_template_args", LangOpts.CPlusPlus11)

test/CodeGenCXX/builtins.cpp

@@ -26,3 +26,7 @@ int x = __builtin_abs(-2);
 long y = __builtin_abs(-2l);
 // CHECK:  [[Y:%.+]] = call i64 @_Z13__builtin_absl(i64 -2)
 // CHECK:  store i64 [[Y]], i64* @y, align 8
+
+extern const char char_memchr_arg[32];
+char *memchr_result = __builtin_char_memchr(char_memchr_arg, 123, 32);
+// CHECK: call i8* @memchr(i8* getelementptr inbounds ([32 x i8], [32 x i8]* @char_memchr_arg, i32 0, i32 0), i32 123, i64 32)

test/Lexer/has_feature_cxx0x.cpp

@@ -301,6 +301,17 @@ int no_constexpr();
 // CHECK-11: has_constexpr
 // CHECK-NO-11: no_constexpr
 
+#if __has_feature(cxx_constexpr_string_builtins)
+int has_constexpr_string_builtins();
+#else
+int no_constexpr_string_builtins();
+#endif
+
+// CHECK-1Z: has_constexpr_string_builtins
+// CHECK-14: has_constexpr_string_builtins
+// CHECK-11: has_constexpr_string_builtins
+// CHECK-NO-11: no_constexpr_string_builtins
+
 #if __has_feature(cxx_generalized_initializers)
 int has_generalized_initializers();
 #else

test/SemaCXX/constexpr-string.cpp

@@ -166,6 +166,27 @@ namespace StrchrEtc {
   static_assert(__builtin_memchr(nullptr, 'x', 3) == nullptr); // expected-error {{not an integral constant}} expected-note {{dereferenced null}}
   static_assert(__builtin_memchr(nullptr, 'x', 0) == nullptr); // FIXME: Should we reject this?
 
+  static_assert(__builtin_char_memchr(kStr, 'a', 0) == nullptr);
+  static_assert(__builtin_char_memchr(kStr, 'a', 1) == kStr);
+  static_assert(__builtin_char_memchr(kStr, '\0', 5) == nullptr);
+  static_assert(__builtin_char_memchr(kStr, '\0', 6) == kStr + 5);
+  static_assert(__builtin_char_memchr(kStr, '\xff', 8) == kStr + 4);
+  static_assert(__builtin_char_memchr(kStr, '\xff' + 256, 8) == kStr + 4);
+  static_assert(__builtin_char_memchr(kStr, '\xff' - 256, 8) == kStr + 4);
+  static_assert(__builtin_char_memchr(kFoo, 'x', 3) == nullptr);
+  static_assert(__builtin_char_memchr(kFoo, 'x', 4) == nullptr); // expected-error {{not an integral constant}} expected-note {{dereferenced one-past-the-end}}
+  static_assert(__builtin_char_memchr(nullptr, 'x', 3) == nullptr); // expected-error {{not an integral constant}} expected-note {{dereferenced null}}
+  static_assert(__builtin_char_memchr(nullptr, 'x', 0) == nullptr); // FIXME: Should we reject this?
+
+  static_assert(*__builtin_char_memchr(kStr, '\xff', 8) == '\xff');
+  constexpr bool char_memchr_mutable() {
+    char buffer[] = "mutable";
+    *__builtin_char_memchr(buffer, 't', 8) = 'r';
+    *__builtin_char_memchr(buffer, 'm', 8) = 'd';
+    return __builtin_strcmp(buffer, "durable") == 0;
+  }
+  static_assert(char_memchr_mutable());
+
   constexpr bool a = !strchr("hello", 'h'); // expected-error {{constant expression}} expected-note {{non-constexpr function 'strchr' cannot be used in a constant expression}}
   constexpr bool b = !memchr("hello", 'h', 3); // expected-error {{constant expression}} expected-note {{non-constexpr function 'memchr' cannot be used in a constant expression}}
 }