[clang] 00d3e6c - [c++17] Implement P0145R3 during constant evaluation.
Richard Smith via cfe-commits
cfe-commits at lists.llvm.org
Tue Oct 6 12:33:45 PDT 2020
Author: Richard Smith
Date: 2020-10-06T12:30:26-07:00
New Revision: 00d3e6c1b4d0b7879afc6002b721111b49ecf755
URL: https://github.com/llvm/llvm-project/commit/00d3e6c1b4d0b7879afc6002b721111b49ecf755
DIFF: https://github.com/llvm/llvm-project/commit/00d3e6c1b4d0b7879afc6002b721111b49ecf755.diff
LOG: [c++17] Implement P0145R3 during constant evaluation.
Ensure that we evaluate assignment and compound-assignment
right-to-left, and array subscripting left-to-right.
Fixes PR47724.
This is a re-commit of ded79be, reverted in 37c74df, with a fix and test
for the crasher bug previously introduced.
Added:
Modified:
clang/lib/AST/ExprConstant.cpp
clang/test/SemaCXX/constant-expression-cxx1z.cpp
clang/www/cxx_status.html
Removed:
################################################################################
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 4460e3a17e6d..639a5733b34b 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -1856,8 +1856,12 @@ void CallStackFrame::describe(raw_ostream &Out) {
Out << ", ";
const ParmVarDecl *Param = *I;
- const APValue &Arg = Arguments[ArgIndex];
- Arg.printPretty(Out, Info.Ctx, Param->getType());
+ if (Arguments) {
+ const APValue &Arg = Arguments[ArgIndex];
+ Arg.printPretty(Out, Info.Ctx, Param->getType());
+ } else {
+ Out << "<...>";
+ }
if (ArgIndex == 0 && IsMemberCall)
Out << "->" << *Callee << '(';
@@ -5792,6 +5796,8 @@ typedef SmallVector<APValue, 8> ArgVector;
/// EvaluateArgs - Evaluate the arguments to a function call.
static bool EvaluateArgs(ArrayRef<const Expr *> Args, ArgVector &ArgValues,
EvalInfo &Info, const FunctionDecl *Callee) {
+ ArgValues.resize(Args.size());
+
bool Success = true;
llvm::SmallBitVector ForbiddenNullArgs;
if (Callee->hasAttr<NonNullAttr>()) {
@@ -5809,8 +5815,6 @@ static bool EvaluateArgs(ArrayRef<const Expr *> Args, ArgVector &ArgValues,
}
}
}
- // FIXME: This is the wrong evaluation order for an assignment operator
- // called via operator syntax.
for (unsigned Idx = 0; Idx < Args.size(); Idx++) {
if (!Evaluate(ArgValues[Idx], Info, Args[Idx])) {
// If we're checking for a potential constant expression, evaluate all
@@ -5834,17 +5838,13 @@ static bool EvaluateArgs(ArrayRef<const Expr *> Args, ArgVector &ArgValues,
/// Evaluate a function call.
static bool HandleFunctionCall(SourceLocation CallLoc,
const FunctionDecl *Callee, const LValue *This,
- ArrayRef<const Expr*> Args, const Stmt *Body,
- EvalInfo &Info, APValue &Result,
- const LValue *ResultSlot) {
- ArgVector ArgValues(Args.size());
- if (!EvaluateArgs(Args, ArgValues, Info, Callee))
- return false;
-
+ ArrayRef<const Expr *> Args, APValue *ArgValues,
+ const Stmt *Body, EvalInfo &Info,
+ APValue &Result, const LValue *ResultSlot) {
if (!Info.CheckCallLimit(CallLoc))
return false;
- CallStackFrame Frame(Info, CallLoc, Callee, This, ArgValues.data());
+ CallStackFrame Frame(Info, CallLoc, Callee, This, ArgValues);
// For a trivial copy or move assignment, perform an APValue copy. This is
// essential for unions, where the operations performed by the assignment
@@ -7293,6 +7293,8 @@ class ExprEvaluatorBase
auto Args = llvm::makeArrayRef(E->getArgs(), E->getNumArgs());
bool HasQualifier = false;
+ ArgVector ArgValues;
+
// Extract function decl and 'this' pointer from the callee.
if (CalleeType->isSpecificBuiltinType(BuiltinType::BoundMember)) {
const CXXMethodDecl *Member = nullptr;
@@ -7341,6 +7343,22 @@ class ExprEvaluatorBase
return Error(E);
}
+ // For an (overloaded) assignment expression, evaluate the RHS before the
+ // LHS.
+ auto *OCE = dyn_cast<CXXOperatorCallExpr>(E);
+ if (OCE && OCE->isAssignmentOp()) {
+ assert(Args.size() == 2 && "wrong number of arguments in assignment");
+ if (isa<CXXMethodDecl>(FD)) {
+ // Args[0] is the object argument.
+ if (!EvaluateArgs({Args[1]}, ArgValues, Info, FD))
+ return false;
+ } else {
+ if (!EvaluateArgs({Args[1], Args[0]}, ArgValues, Info, FD))
+ return false;
+ std::swap(ArgValues[0], ArgValues[1]);
+ }
+ }
+
// Overloaded operator calls to member functions are represented as normal
// calls with '*this' as the first argument.
const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(FD);
@@ -7403,6 +7421,11 @@ class ExprEvaluatorBase
} else
return Error(E);
+ // Evaluate the arguments now if we've not already done so.
+ if (ArgValues.empty() && !Args.empty() &&
+ !EvaluateArgs(Args, ArgValues, Info, FD))
+ return false;
+
SmallVector<QualType, 4> CovariantAdjustmentPath;
if (This) {
auto *NamedMember = dyn_cast<CXXMethodDecl>(FD);
@@ -7424,6 +7447,7 @@ class ExprEvaluatorBase
// Destructor calls are
diff erent enough that they have their own codepath.
if (auto *DD = dyn_cast<CXXDestructorDecl>(FD)) {
assert(This && "no 'this' pointer for destructor call");
+ assert(ArgValues.empty() && "unexpected destructor arguments");
return HandleDestruction(Info, E, *This,
Info.Ctx.getRecordType(DD->getParent()));
}
@@ -7432,8 +7456,8 @@ class ExprEvaluatorBase
Stmt *Body = FD->getBody(Definition);
if (!CheckConstexprFunction(Info, E->getExprLoc(), FD, Definition, Body) ||
- !HandleFunctionCall(E->getExprLoc(), Definition, This, Args, Body, Info,
- Result, ResultSlot))
+ !HandleFunctionCall(E->getExprLoc(), Definition, This, Args,
+ ArgValues.data(), Body, Info, Result, ResultSlot))
return false;
if (!CovariantAdjustmentPath.empty() &&
@@ -8071,16 +8095,19 @@ bool LValueExprEvaluator::VisitArraySubscriptExpr(const ArraySubscriptExpr *E) {
if (E->getBase()->getType()->isVectorType())
return Error(E);
+ APSInt Index;
bool Success = true;
- if (!evaluatePointer(E->getBase(), Result)) {
- if (!Info.noteFailure())
- return false;
- Success = false;
- }
- APSInt Index;
- if (!EvaluateInteger(E->getIdx(), Index, Info))
- return false;
+ // C++17's rules require us to evaluate the LHS first, regardless of which
+ // side is the base.
+ for (const Expr *SubExpr : {E->getLHS(), E->getRHS()}) {
+ if (SubExpr == E->getBase() ? !evaluatePointer(SubExpr, Result)
+ : !EvaluateInteger(SubExpr, Index, Info)) {
+ if (!Info.noteFailure())
+ return false;
+ Success = false;
+ }
+ }
return Success &&
HandleLValueArrayAdjustment(Info, E, Result, E->getType(), Index);
@@ -8125,16 +8152,18 @@ bool LValueExprEvaluator::VisitCompoundAssignOperator(
if (!Info.getLangOpts().CPlusPlus14 && !Info.keepEvaluatingAfterFailure())
return Error(CAO);
- APValue RHS;
+ bool Success = true;
- // The overall lvalue result is the result of evaluating the LHS.
- if (!this->Visit(CAO->getLHS())) {
- if (Info.noteFailure())
- Evaluate(RHS, this->Info, CAO->getRHS());
- return false;
+ // C++17 onwards require that we evaluate the RHS first.
+ APValue RHS;
+ if (!Evaluate(RHS, this->Info, CAO->getRHS())) {
+ if (!Info.noteFailure())
+ return false;
+ Success = false;
}
- if (!Evaluate(RHS, this->Info, CAO->getRHS()))
+ // The overall lvalue result is the result of evaluating the LHS.
+ if (!this->Visit(CAO->getLHS()) || !Success)
return false;
return handleCompoundAssignment(
@@ -8147,15 +8176,17 @@ bool LValueExprEvaluator::VisitBinAssign(const BinaryOperator *E) {
if (!Info.getLangOpts().CPlusPlus14 && !Info.keepEvaluatingAfterFailure())
return Error(E);
- APValue NewVal;
+ bool Success = true;
- if (!this->Visit(E->getLHS())) {
- if (Info.noteFailure())
- Evaluate(NewVal, this->Info, E->getRHS());
- return false;
+ // C++17 onwards require that we evaluate the RHS first.
+ APValue NewVal;
+ if (!Evaluate(NewVal, this->Info, E->getRHS())) {
+ if (!Info.noteFailure())
+ return false;
+ Success = false;
}
- if (!Evaluate(NewVal, this->Info, E->getRHS()))
+ if (!this->Visit(E->getLHS()) || !Success)
return false;
if (Info.getLangOpts().CPlusPlus20 &&
@@ -15270,7 +15301,8 @@ bool Expr::isPotentialConstantExpr(const FunctionDecl *FD,
} else {
SourceLocation Loc = FD->getLocation();
HandleFunctionCall(Loc, FD, (MD && MD->isInstance()) ? &This : nullptr,
- Args, FD->getBody(), Info, Scratch, nullptr);
+ Args, /*ArgValues*/ nullptr, FD->getBody(), Info,
+ Scratch, nullptr);
}
return Diags.empty();
@@ -15292,13 +15324,8 @@ bool Expr::isPotentialConstantExprUnevaluated(Expr *E,
Info.CheckingPotentialConstantExpression = true;
// Fabricate a call stack frame to give the arguments a plausible cover story.
- ArrayRef<const Expr*> Args;
- ArgVector ArgValues(0);
- bool Success = EvaluateArgs(Args, ArgValues, Info, FD);
- (void)Success;
- assert(Success &&
- "Failed to set up arguments for potential constant evaluation");
- CallStackFrame Frame(Info, SourceLocation(), FD, nullptr, ArgValues.data());
+ CallStackFrame Frame(Info, SourceLocation(), FD, /*This*/ nullptr,
+ /*ArgValues*/ nullptr);
APValue ResultScratch;
Evaluate(ResultScratch, Info, E);
diff --git a/clang/test/SemaCXX/constant-expression-cxx1z.cpp b/clang/test/SemaCXX/constant-expression-cxx1z.cpp
index 2b366adf2e91..9335626a5c90 100644
--- a/clang/test/SemaCXX/constant-expression-cxx1z.cpp
+++ b/clang/test/SemaCXX/constant-expression-cxx1z.cpp
@@ -59,3 +59,121 @@ void test() {
else if constexpr (v<int>) {}
}
}
+
+// Check that assignment operators evaluate their operands right-to-left.
+namespace EvalOrder {
+ template<typename T> struct lvalue {
+ T t;
+ constexpr T &get() { return t; }
+ };
+
+ struct UserDefined {
+ int n = 0;
+ constexpr UserDefined &operator=(const UserDefined&) { return *this; }
+ constexpr UserDefined &operator+=(const UserDefined&) { return *this; }
+ constexpr void operator<<(const UserDefined&) const {}
+ constexpr void operator>>(const UserDefined&) const {}
+ constexpr void operator+(const UserDefined&) const {}
+ constexpr void operator[](int) const {}
+ };
+ constexpr UserDefined ud;
+
+ struct NonMember {};
+ constexpr void operator+=(NonMember, NonMember) {}
+ constexpr void operator<<(NonMember, NonMember) {}
+ constexpr void operator>>(NonMember, NonMember) {}
+ constexpr void operator+(NonMember, NonMember) {}
+ constexpr NonMember nm;
+
+ constexpr void f(...) {}
+
+ // Helper to ensure that 'a' is evaluated before 'b'.
+ struct seq_checker {
+ bool done_a = false;
+ bool done_b = false;
+
+ template <typename T> constexpr T &&a(T &&v) {
+ done_a = true;
+ return (T &&)v;
+ }
+ template <typename T> constexpr T &&b(T &&v) {
+ if (!done_a)
+ throw "wrong";
+ done_b = true;
+ return (T &&)v;
+ }
+
+ constexpr bool ok() { return done_a && done_b; }
+ };
+
+ // SEQ(expr), where part of the expression is tagged A(...) and part is
+ // tagged B(...), checks that A is evaluated before B.
+ #define A sc.a
+ #define B sc.b
+ #define SEQ(...) static_assert([](seq_checker sc) { void(__VA_ARGS__); return sc.ok(); }({}))
+
+ // Longstanding sequencing rules.
+ SEQ((A(1), B(2)));
+ SEQ((A(true) ? B(2) : throw "huh?"));
+ SEQ((A(false) ? throw "huh?" : B(2)));
+ SEQ(A(true) && B(true));
+ SEQ(A(false) || B(true));
+
+ // From P0145R3:
+
+ // Rules 1 and 2 have no effect ('b' is not an expression).
+
+ // Rule 3: a->*b
+ SEQ(A(ud).*B(&UserDefined::n));
+ SEQ(A(&ud)->*B(&UserDefined::n));
+
+ // Rule 4: a(b1, b2, b3)
+ SEQ(A(f)(B(1), B(2), B(3)));
+
+ // Rule 5: b = a, b @= a
+ SEQ(B(lvalue<int>().get()) = A(0));
+ SEQ(B(lvalue<UserDefined>().get()) = A(ud));
+ SEQ(B(lvalue<int>().get()) += A(0));
+ SEQ(B(lvalue<UserDefined>().get()) += A(ud));
+ SEQ(B(lvalue<NonMember>().get()) += A(nm));
+
+ // Rule 6: a[b]
+ constexpr int arr[3] = {};
+ SEQ(A(arr)[B(0)]);
+ SEQ(A(+arr)[B(0)]);
+ SEQ(A(0)[B(arr)]);
+ SEQ(A(0)[B(+arr)]);
+ SEQ(A(ud)[B(0)]);
+
+ // Rule 7: a << b
+ SEQ(A(1) << B(2));
+ SEQ(A(ud) << B(ud));
+ SEQ(A(nm) << B(nm));
+
+ // Rule 8: a >> b
+ SEQ(A(1) >> B(2));
+ SEQ(A(ud) >> B(ud));
+ SEQ(A(nm) >> B(nm));
+
+ // No particular order of evaluation is specified in other cases, but we in
+ // practice evaluate left-to-right.
+ // FIXME: Technically we're expected to check for undefined behavior due to
+ // unsequenced read and modification and treat it as non-constant due to UB.
+ SEQ(A(1) + B(2));
+ SEQ(A(ud) + B(ud));
+ SEQ(A(nm) + B(nm));
+ SEQ(f(A(1), B(2)));
+
+ #undef SEQ
+ #undef A
+ #undef B
+}
+
+namespace LambdaCallOp {
+ constexpr void get_lambda(void (*&p)()) { p = []{}; }
+ constexpr void call_lambda() {
+ void (*p)() = nullptr;
+ get_lambda(p);
+ p();
+ }
+}
diff --git a/clang/www/cxx_status.html b/clang/www/cxx_status.html
index 3c546eb409de..9c39e396edd4 100755
--- a/clang/www/cxx_status.html
+++ b/clang/www/cxx_status.html
@@ -807,6 +807,7 @@ <h2 id="cxx17">C++17 implementation status</h2>
<tt>operator&&</tt>, <tt>operator||</tt>, and <tt>operator,</tt>
functions using expression syntax are no longer guaranteed to be destroyed in
reverse construction order in that ABI.
+This is not fully supported during constant expression evaluation until Clang 12.
</span><br>
<span id="p0522">(10): Despite being the resolution to a Defect Report, this
feature is disabled by default in all language versions, and can be enabled
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