Author: rsmith
Date: Tue Apr 23 18:29:28 2019
New Revision: 359059
URL: http://llvm.org/viewvc/llvm-project?rev=359059&view=rev
Log:
Fix interactions between __builtin_constant_p and constexpr to match
current trunk GCC.
GCC permits information from outside the operand of
__builtin_constant_p (but in the same constant evaluation context) to be
used within that operand; clang now does so too. A few other minor
deviations from GCC's behavior showed up in my testing and are also
fixed (matching GCC):
* Clang now supports nullptr_t as the argument type for
__builtin_constant_p
* Clang now returns true from __builtin_constant_p if called with a
null pointer
* Clang now returns true from __builtin_constant_p if called with an
integer cast to pointer type
Added:
cfe/trunk/test/SemaCXX/builtin-constant-p.cpp
Modified:
cfe/trunk/lib/AST/ExprConstant.cpp
cfe/trunk/lib/Sema/SemaChecking.cpp
cfe/trunk/test/SemaCXX/enable_if.cpp
Modified: cfe/trunk/lib/AST/ExprConstant.cpp
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/ExprConstant.cpp?rev=359059&r1=359058&r2=359059&view=diff
==============================================================================
--- cfe/trunk/lib/AST/ExprConstant.cpp (original)
+++ cfe/trunk/lib/AST/ExprConstant.cpp Tue Apr 23 18:29:28 2019
@@ -7801,19 +7801,33 @@ EvaluateBuiltinClassifyType(const CallEx
}
/// EvaluateBuiltinConstantPForLValue - Determine the result of
-/// __builtin_constant_p when applied to the given lvalue.
+/// __builtin_constant_p when applied to the given pointer.
///
-/// An lvalue is only "constant" if it is a pointer or reference to the first
-/// character of a string literal.
-template<typename LValue>
-static bool EvaluateBuiltinConstantPForLValue(const LValue &LV) {
- const Expr *E = LV.getLValueBase().template dyn_cast<const Expr*>();
- return E && isa<StringLiteral>(E) && LV.getLValueOffset().isZero();
+/// A pointer is only "constant" if it is null (or a pointer cast to integer)
+/// or it points to the first character of a string literal.
+static bool EvaluateBuiltinConstantPForLValue(const APValue &LV) {
+ APValue::LValueBase Base = LV.getLValueBase();
+ if (Base.isNull()) {
+ // A null base is acceptable.
+ return true;
+ } else if (const Expr *E = Base.dyn_cast<const Expr *>()) {
+ if (!isa<StringLiteral>(E))
+ return false;
+ return LV.getLValueOffset().isZero();
+ } else {
+ // Any other base is not constant enough for GCC.
+ return false;
+ }
}
/// EvaluateBuiltinConstantP - Evaluate __builtin_constant_p as similarly to
/// GCC as we can manage.
-static bool EvaluateBuiltinConstantP(ASTContext &Ctx, const Expr *Arg) {
+static bool EvaluateBuiltinConstantP(EvalInfo &Info, const Expr *Arg) {
+ // Constant-folding is always enabled for the operand of __builtin_constant_p
+ // (even when the enclosing evaluation context otherwise requires a strict
+ // language-specific constant expression).
+ FoldConstant Fold(Info, true);
+
QualType ArgType = Arg->getType();
// __builtin_constant_p always has one operand. The rules which gcc follows
@@ -7821,34 +7835,27 @@ static bool EvaluateBuiltinConstantP(AST
//
// - If the operand is of integral, floating, complex or enumeration type,
// and can be folded to a known value of that type, it returns 1.
- // - If the operand and can be folded to a pointer to the first character
- // of a string literal (or such a pointer cast to an integral type), it
- // returns 1.
+ // - If the operand can be folded to a pointer to the first character
+ // of a string literal (or such a pointer cast to an integral type)
+ // or to a null pointer or an integer cast to a pointer, it returns 1.
//
// Otherwise, it returns 0.
//
// FIXME: GCC also intends to return 1 for literals of aggregate types, but
// its support for this does not currently work.
- if (ArgType->isIntegralOrEnumerationType()) {
- Expr::EvalResult Result;
- if (!Arg->EvaluateAsRValue(Result, Ctx) || Result.HasSideEffects)
+ if (ArgType->isIntegralOrEnumerationType() || ArgType->isFloatingType() ||
+ ArgType->isAnyComplexType() || ArgType->isPointerType() ||
+ ArgType->isNullPtrType()) {
+ APValue V;
+ if (!::EvaluateAsRValue(Info, Arg, V))
return false;
- APValue &V = Result.Val;
- if (V.getKind() == APValue::Int)
- return true;
+ // For a pointer (possibly cast to integer), there are special rules.
if (V.getKind() == APValue::LValue)
return EvaluateBuiltinConstantPForLValue(V);
- } else if (ArgType->isFloatingType() || ArgType->isAnyComplexType()) {
- return Arg->isEvaluatable(Ctx);
- } else if (ArgType->isPointerType() || Arg->isGLValue()) {
- LValue LV;
- Expr::EvalStatus Status;
- EvalInfo Info(Ctx, Status, EvalInfo::EM_ConstantFold);
- if ((Arg->isGLValue() ? EvaluateLValue(Arg, LV, Info)
- : EvaluatePointer(Arg, LV, Info)) &&
- !Status.HasSideEffects)
- return EvaluateBuiltinConstantPForLValue(LV);
+
+ // Otherwise, any constant value is good enough.
+ return V.getKind() != APValue::Uninitialized;
}
// Anything else isn't considered to be sufficiently constant.
@@ -8259,7 +8266,7 @@ bool IntExprEvaluator::VisitBuiltinCallE
case Builtin::BI__builtin_constant_p: {
auto Arg = E->getArg(0);
- if (EvaluateBuiltinConstantP(Info.Ctx, Arg))
+ if (EvaluateBuiltinConstantP(Info, Arg))
return Success(true, E);
auto ArgTy = Arg->IgnoreImplicit()->getType();
if (!Info.InConstantContext && !Arg->HasSideEffects(Info.Ctx) &&
Modified: cfe/trunk/lib/Sema/SemaChecking.cpp
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaChecking.cpp?rev=359059&r1=359058&r2=359059&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaChecking.cpp (original)
+++ cfe/trunk/lib/Sema/SemaChecking.cpp Tue Apr 23 18:29:28 2019
@@ -1199,10 +1199,14 @@ Sema::CheckBuiltinFunctionCall(FunctionD
if (checkArgCount(*this, TheCall, 1)) return true;
TheCall->setType(Context.IntTy);
break;
- case Builtin::BI__builtin_constant_p:
+ case Builtin::BI__builtin_constant_p: {
if (checkArgCount(*this, TheCall, 1)) return true;
+ ExprResult Arg = DefaultFunctionArrayLvalueConversion(TheCall->getArg(0));
+ if (Arg.isInvalid()) return true;
+ TheCall->setArg(0, Arg.get());
TheCall->setType(Context.IntTy);
break;
+ }
case Builtin::BI__builtin_launder:
return SemaBuiltinLaunder(*this, TheCall);
case Builtin::BI__sync_fetch_and_add:
Added: cfe/trunk/test/SemaCXX/builtin-constant-p.cpp
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/builtin-constant-p.cpp?rev=359059&view=auto
==============================================================================
--- cfe/trunk/test/SemaCXX/builtin-constant-p.cpp (added)
+++ cfe/trunk/test/SemaCXX/builtin-constant-p.cpp Tue Apr 23 18:29:28 2019
@@ -0,0 +1,61 @@
+// RUN: %clang_cc1 -std=c++17 -verify %s
+
+using intptr_t = __INTPTR_TYPE__;
+
+// Test interaction of constexpr and __builtin_constant_p.
+
+template<typename T> constexpr bool bcp(T t) {
+ return __builtin_constant_p(t);
+}
+template<typename T> constexpr bool bcp_fold(T t) {
+ return __builtin_constant_p(((void)(intptr_t)&t, t));
+}
+
+constexpr intptr_t ensure_fold_is_generally_not_enabled = // expected-error
{{constant expression}}
+ (intptr_t)&ensure_fold_is_generally_not_enabled; // expected-note {{cast}}
+
+constexpr intptr_t ptr_to_int(const void *p) {
+ return __builtin_constant_p(1) ? (intptr_t)p : (intptr_t)p;
+}
+
+constexpr int *int_to_ptr(intptr_t n) {
+ return __builtin_constant_p(1) ? (int*)n : (int*)n;
+}
+
+int x;
+
+// Integer and floating point constants encountered during constant expression
+// evaluation are considered constant. So is nullptr_t.
+static_assert(bcp(1));
+static_assert(bcp_fold(1));
+static_assert(bcp(1.0));
+static_assert(bcp_fold(1.0));
+static_assert(bcp(nullptr));
+static_assert(bcp_fold(nullptr));
+
+// Pointers to the start of strings are considered constant.
+static_assert(bcp("foo"));
+static_assert(bcp_fold("foo"));
+
+// Null pointers are considered constant.
+static_assert(bcp<int*>(nullptr));
+static_assert(bcp_fold<int*>(nullptr));
+static_assert(bcp<const char*>(nullptr));
+static_assert(bcp_fold<const char*>(nullptr));
+
+// Other pointers are not.
+static_assert(!bcp(&x));
+static_assert(!bcp_fold(&x));
+
+// Pointers cast to integers follow the rules for pointers.
+static_assert(bcp(ptr_to_int("foo")));
+static_assert(bcp_fold(ptr_to_int("foo")));
+static_assert(!bcp(ptr_to_int(&x)));
+static_assert(!bcp_fold(ptr_to_int(&x)));
+
+// Integers cast to pointers follow the integer rules.
+static_assert(bcp(int_to_ptr(0)));
+static_assert(bcp_fold(int_to_ptr(0)));
+static_assert(bcp(int_to_ptr(123))); // GCC rejects these due to not
recognizing
+static_assert(bcp_fold(int_to_ptr(123))); // the bcp conditional in
'int_to_ptr' ...
+static_assert(__builtin_constant_p((int*)123)); // ... but GCC accepts this
Modified: cfe/trunk/test/SemaCXX/enable_if.cpp
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/enable_if.cpp?rev=359059&r1=359058&r2=359059&view=diff
==============================================================================
--- cfe/trunk/test/SemaCXX/enable_if.cpp (original)
+++ cfe/trunk/test/SemaCXX/enable_if.cpp Tue Apr 23 18:29:28 2019
@@ -522,3 +522,14 @@ void test() {
InConstantContext::foo("abc");
}
} // namespace InConstantContext
+
+namespace StringLiteralDetector {
+ void need_string_literal(const char *p)
__attribute__((enable_if(__builtin_constant_p(p), "argument is not a string
literal"))); // expected-note 2{{not a string literal}}
+ void test(const char *unknown) {
+ need_string_literal("foo");
+ need_string_literal(unknown); // expected-error {{no matching function}}
+ constexpr char str[] = "bar";
+ need_string_literal(str); // expected-error {{no matching function}}
+ }
+}
+
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