https://github.com/Tsche updated
https://github.com/llvm/llvm-project/pull/160440
>From a9d97d453d6d6587ec28aee9381020b1cbd54412 Mon Sep 17 00:00:00 2001
From: Tsche <c...@pydong.org>
Date: Wed, 24 Sep 2025 07:09:29 +0200
Subject: [PATCH 1/3] [clang] introduce constexpr step limit opt-out
---
clang/docs/UsersManual.rst | 2 +-
clang/lib/AST/ByteCode/Interp.h | 3 +++
clang/lib/AST/ExprConstant.cpp | 5 ++++-
3 files changed, 8 insertions(+), 2 deletions(-)
diff --git a/clang/docs/UsersManual.rst b/clang/docs/UsersManual.rst
index a8bbf146431ea..1a062475728dd 100644
--- a/clang/docs/UsersManual.rst
+++ b/clang/docs/UsersManual.rst
@@ -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
diff --git a/clang/lib/AST/ByteCode/Interp.h b/clang/lib/AST/ByteCode/Interp.h
index b3b4b998439cc..deba2d294abe9 100644
--- a/clang/lib/AST/ByteCode/Interp.h
+++ b/clang/lib/AST/ByteCode/Interp.h
@@ -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)
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index d10e2afeb2341..0fe3fce5b64a8 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -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;
@@ -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;
>From 40fe30d71f3a0fc45662267112cad978e27c7df6 Mon Sep 17 00:00:00 2001
From: Tsche <c...@pydong.org>
Date: Wed, 24 Sep 2025 17:21:57 +0200
Subject: [PATCH 2/3] [clang] add help text for constexpr step limit opt-out
---
clang/include/clang/Driver/Options.td | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/clang/include/clang/Driver/Options.td
b/clang/include/clang/Driver/Options.td
index 77f19a240a7f9..ddf984a5ab447 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -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">,
>From 747856a3998040dec8de031d071a8ba952aa16e6 Mon Sep 17 00:00:00 2001
From: Tsche <c...@pydong.org>
Date: Wed, 24 Sep 2025 18:19:34 +0200
Subject: [PATCH 3/3] [clang] add release note for constexpr step limit opt-out
---
clang/docs/ReleaseNotes.rst | 1 +
1 file changed, 1 insertion(+)
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 70c82b090107a..50b5f2cb3ee16 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -258,6 +258,7 @@ Deprecated Compiler Flags
Modified Compiler Flags
-----------------------
- The `-gkey-instructions` compiler flag is now enabled by default when DWARF
is emitted for plain C/C++ and optimizations are enabled. (#GH149509)
+- The `-fconstexpr-steps` compiler flag now accepts value `0` to opt out of
this limit. (#GH160440)
Removed Compiler Flags
-------------------------
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