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[clang] introduce constexpr step limit opt-out #160440

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Merged
AaronBallman merged 6 commits into from
Oct 13, 2025
Merged

[clang] introduce constexpr step limit opt-out #160440

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a9d97d4
[clang] introduce constexpr step limit opt-out
Tsche Sep 24, 2025
40fe30d
[clang] add help text for constexpr step limit opt-out
Tsche Sep 24, 2025
747856a
[clang] add release note for constexpr step limit opt-out
Tsche Sep 24, 2025
1eb7f6d
[clang] add step limit opt-out to keepEvaluatingAfterFailure, clean u…
Tsche Oct 13, 2025
e763cb6
[clang] remove accidental full stop at the end of the sentence
Tsche Oct 13, 2025
f1cba7e
Merge branch 'main' into constexpr_steps
Tsche Oct 13, 2025
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2 changes: 1 addition & 1 deletion clang/docs/UsersManual.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -4028,7 +4028,7 @@ Controlling implementation limits
Sets the limit for the number of full-expressions evaluated in a single
constant expression evaluation. This also controls the maximum size
of array and dynamic array allocation that can be constant evaluated.
The default is 1048576.
The default is 1048576, and the limit can be disabled with `-fconstexpr-steps=0`..

.. option:: -ftemplate-depth=N

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2 changes: 1 addition & 1 deletion clang/include/clang/Driver/Options.td
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Expand Up @@ -2045,7 +2045,7 @@ def fconstexpr_depth_EQ : Joined<["-"], "fconstexpr-depth=">, Group<f_Group>,
MarshallingInfoInt<LangOpts<"ConstexprCallDepth">, "512">;
def fconstexpr_steps_EQ : Joined<["-"], "fconstexpr-steps=">, Group<f_Group>,
Visibility<[ClangOption, CC1Option]>,
HelpText<"Set the maximum number of steps in constexpr function evaluation">,
HelpText<"Set the maximum number of steps in constexpr function evaluation (0 = no limit)">,
MarshallingInfoInt<LangOpts<"ConstexprStepLimit">, "1048576">;
def fexperimental_new_constant_interpreter : Flag<["-"], "fexperimental-new-constant-interpreter">, Group<f_Group>,
HelpText<"Enable the experimental new constant interpreter">,
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3 changes: 3 additions & 0 deletions clang/lib/AST/ByteCode/Interp.h
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Expand Up @@ -3686,6 +3686,9 @@ inline bool CheckDestruction(InterpState &S, CodePtr OpPC) {

inline bool CheckArraySize(InterpState &S, CodePtr OpPC, uint64_t NumElems) {
uint64_t Limit = S.getLangOpts().ConstexprStepLimit;
if (Limit == 0)
return true;

if (NumElems > Limit) {
S.FFDiag(S.Current->getSource(OpPC),
diag::note_constexpr_new_exceeds_limits)
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5 changes: 4 additions & 1 deletion clang/lib/AST/ExprConstant.cpp
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Expand Up @@ -990,7 +990,7 @@ namespace {
// of arrays to avoid exhausting the system resources, as initialization
// of each element is likely to take some number of steps anyway.
uint64_t Limit = Ctx.getLangOpts().ConstexprStepLimit;
if (ElemCount > Limit) {
if (Limit != 0 && ElemCount > Limit) {
if (Diag)
FFDiag(Loc, diag::note_constexpr_new_exceeds_limits)
<< ElemCount << Limit;
Expand All @@ -1016,6 +1016,9 @@ namespace {
}

bool nextStep(const Stmt *S) {
if (Ctx.getLangOpts().ConstexprStepLimit == 0)
return true;

if (!StepsLeft) {
FFDiag(S->getBeginLoc(), diag::note_constexpr_step_limit_exceeded);
return false;
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