Commit a3d3bd21 authored by Richard Smith's avatar Richard Smith
Browse files

C++1y: Add a step limit to constexpr evaluation, to catch runaway loops. 

llvm-svn: 181388
parent 1aee70b7

clang/include/clang/Basic/DiagnosticASTKinds.td

+2 −0
Original line number Diff line number Diff line
@@ -83,6 +83,8 @@ def note_constexpr_depth_limit_exceeded : Note< 
  "constexpr evaluation exceeded maximum depth of %0 calls">;

def note_constexpr_call_limit_exceeded : Note<

  "constexpr evaluation hit maximum call limit">;

def note_constexpr_step_limit_exceeded : Note<

  "constexpr evaluation hit maximum step limit; possible infinite loop?">;

def note_constexpr_lifetime_ended : Note<

  "%select{read of|assignment to|increment of|decrement of}0 "

  "%select{temporary|variable}1 whose lifetime has ended">;

clang/include/clang/Basic/LangOptions.def

+2 −0
Original line number Diff line number Diff line
@@ -160,6 +160,8 @@ BENIGN_LANGOPT(InstantiationDepth, 32, 256, 
               "maximum template instantiation depth")

BENIGN_LANGOPT(ConstexprCallDepth, 32, 512,

               "maximum constexpr call depth")

BENIGN_LANGOPT(ConstexprStepLimit, 32, 1048576,

               "maximum constexpr evaluation steps")

BENIGN_LANGOPT(BracketDepth, 32, 256,

               "maximum bracket nesting depth")

BENIGN_LANGOPT(NumLargeByValueCopy, 32, 0,

clang/include/clang/Driver/CC1Options.td

+2 −0
Original line number Diff line number Diff line
@@ -434,6 +434,8 @@ def ftemplate_depth : Separate<["-"], "ftemplate-depth">, 
  HelpText<"Maximum depth of recursive template instantiation">;

def fconstexpr_depth : Separate<["-"], "fconstexpr-depth">,

  HelpText<"Maximum depth of recursive constexpr function calls">;

def fconstexpr_steps : Separate<["-"], "fconstexpr-steps">,

  HelpText<"Maximum number of steps in constexpr function evaluation">;

def fbracket_depth : Separate<["-"], "fbracket-depth">,

  HelpText<"Maximum nesting level for parentheses, brackets, and braces">;

def fconst_strings : Flag<["-"], "fconst-strings">,

clang/include/clang/Driver/Options.td

+1 −0
Original line number Diff line number Diff line
@@ -344,6 +344,7 @@ def fcompile_resource_EQ : Joined<["-"], "fcompile-resource=">, Group<f_Group>; 
def fconstant_cfstrings : Flag<["-"], "fconstant-cfstrings">, Group<f_Group>;

def fconstant_string_class_EQ : Joined<["-"], "fconstant-string-class=">, Group<f_Group>;

def fconstexpr_depth_EQ : Joined<["-"], "fconstexpr-depth=">, Group<f_Group>;

def fconstexpr_steps_EQ : Joined<["-"], "fconstexpr-steps=">, Group<f_Group>;

def fconstexpr_backtrace_limit_EQ : Joined<["-"], "fconstexpr-backtrace-limit=">,

                                    Group<f_Group>;

def fno_crash_diagnostics : Flag<["-"], "fno-crash-diagnostics">, Group<f_clang_Group>, Flags<[NoArgumentUnused]>;

clang/lib/AST/ExprConstant.cpp

+22 −4
Original line number Diff line number Diff line
@@ -380,6 +380,11 @@ namespace { 
    /// NextCallIndex - The next call index to assign.

    unsigned NextCallIndex;



    /// StepsLeft - The remaining number of evaluation steps we're permitted

    /// to perform. This is essentially a limit for the number of statements

    /// we will evaluate.

    unsigned StepsLeft;



    /// BottomFrame - The frame in which evaluation started. This must be

    /// initialized after CurrentCall and CallStackDepth.

    CallStackFrame BottomFrame;
@@ -407,6 +412,7 @@ namespace { 
             bool OverflowCheckMode = false)

      : Ctx(const_cast<ASTContext&>(C)), EvalStatus(S), CurrentCall(0),

        CallStackDepth(0), NextCallIndex(1),

        StepsLeft(getLangOpts().ConstexprStepLimit),

        BottomFrame(*this, SourceLocation(), 0, 0, 0),

        EvaluatingDecl(0), EvaluatingDeclValue(0), HasActiveDiagnostic(false),

        CheckingPotentialConstantExpression(false),
@@ -446,6 +452,15 @@ namespace { 
      return (Frame->Index == CallIndex) ? Frame : 0;

    }



    bool nextStep(const Stmt *S) {

      if (!StepsLeft) {

        Diag(S->getLocStart(), diag::note_constexpr_step_limit_exceeded);

        return false;

      }

      --StepsLeft;

      return true;

    }



  private:

    /// Add a diagnostic to the diagnostics list.

    PartialDiagnostic &addDiag(SourceLocation Loc, diag::kind DiagId) {
@@ -530,9 +545,9 @@ namespace { 
    bool keepEvaluatingAfterFailure() {

      // Should return true in IntOverflowCheckMode, so that we check for

      // overflow even if some subexpressions can't be evaluated as constants.

      return IntOverflowCheckMode ||

      return StepsLeft && (IntOverflowCheckMode ||

                           (CheckingPotentialConstantExpression &&

              EvalStatus.Diag && EvalStatus.Diag->empty());

                            EvalStatus.Diag && EvalStatus.Diag->empty()));

    }

  };
@@ -2794,6 +2809,9 @@ static EvalStmtResult EvaluateLoopBody(APValue &Result, EvalInfo &Info, 
// Evaluate a statement.

static EvalStmtResult EvaluateStmt(APValue &Result, EvalInfo &Info,

                                   const Stmt *S) {

  if (!Info.nextStep(S))

    return ESR_Failed;



  // FIXME: Mark all temporaries in the current frame as destroyed at

  // the end of each full-expression.

  switch (S->getStmtClass()) {