[clang] [llvm] [AllocToken] Fix and clarify -falloc-token-max=0 (PR #168689)
via llvm-commits
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Wed Nov 19 02:28:29 PST 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: Marco Elver (melver)
<details>
<summary>Changes</summary>
The option -falloc-token-max=0 is supposed to be usable to override previous settings back to the target default max tokens (SIZE_MAX).
This did not work for the builtin:
| executed command: clang -cc1 [..] -nostdsysteminc -triple x86_64-linux-gnu -std=c++23 -fsyntax-only -verify clang/test/SemaCXX/alloc-token.cpp -falloc-token-max=0
| clang: llvm/lib/Support/AllocToken.cpp:38: std::optional<uint64_t> llvm::getAllocToken(AllocTokenMode, const AllocTokenMetadata &, uint64_t): Assertion `MaxTokens && "Must provide non-zero max tokens"' failed.
Fix it by also picking the default if "0" is passed.
Improve the documentation to be clearer what the value of "0" means.
---
Full diff: https://github.com/llvm/llvm-project/pull/168689.diff
7 Files Affected:
- (modified) clang/docs/AllocToken.rst (+3-3)
- (modified) clang/include/clang/Basic/LangOptions.h (+2-2)
- (modified) clang/include/clang/Options/Options.td (+1-1)
- (modified) clang/lib/AST/ByteCode/InterpBuiltin.cpp (+2-1)
- (modified) clang/lib/AST/ExprConstant.cpp (+2-1)
- (modified) clang/test/SemaCXX/alloc-token.cpp (+1)
- (modified) llvm/lib/Transforms/Instrumentation/AllocToken.cpp (+4-3)
``````````diff
diff --git a/clang/docs/AllocToken.rst b/clang/docs/AllocToken.rst
index 1a740e5e22c29..3f319e8be6421 100644
--- a/clang/docs/AllocToken.rst
+++ b/clang/docs/AllocToken.rst
@@ -52,8 +52,8 @@ change or removal. These may (experimentally) be selected with ``-Xclang
The following command-line options affect generated token IDs:
* ``-falloc-token-max=<N>``
- Configures the maximum number of tokens. No max by default (tokens bounded
- by ``SIZE_MAX``).
+ Configures the maximum number of token IDs. By default the number of tokens
+ is bounded by ``SIZE_MAX``.
Querying Token IDs with ``__builtin_infer_alloc_token``
=======================================================
@@ -129,7 +129,7 @@ Fast ABI
--------
An alternative ABI can be enabled with ``-fsanitize-alloc-token-fast-abi``,
-which encodes the token ID hint in the allocation function name.
+which encodes the token ID in the allocation function name.
.. code-block:: c
diff --git a/clang/include/clang/Basic/LangOptions.h b/clang/include/clang/Basic/LangOptions.h
index 8aa89d8c8c807..3f042f8ddb5a1 100644
--- a/clang/include/clang/Basic/LangOptions.h
+++ b/clang/include/clang/Basic/LangOptions.h
@@ -566,8 +566,8 @@ class LangOptions : public LangOptionsBase {
bool AtomicFineGrainedMemory = false;
bool AtomicIgnoreDenormalMode = false;
- /// Maximum number of allocation tokens (0 = no max), nullopt if none set (use
- /// target default).
+ /// Maximum number of allocation tokens (0 = target SIZE_MAX), nullopt if none
+ /// set (use target SIZE_MAX).
std::optional<uint64_t> AllocTokenMax;
/// The allocation token mode.
diff --git a/clang/include/clang/Options/Options.td b/clang/include/clang/Options/Options.td
index cda11fdc94230..786acd6abbd21 100644
--- a/clang/include/clang/Options/Options.td
+++ b/clang/include/clang/Options/Options.td
@@ -2758,7 +2758,7 @@ defm sanitize_alloc_token_extended : BoolOption<"f", "sanitize-alloc-token-exten
def falloc_token_max_EQ : Joined<["-"], "falloc-token-max=">,
Group<f_Group>, Visibility<[ClangOption, CC1Option]>,
MetaVarName<"<N>">,
- HelpText<"Limit to maximum N allocation tokens (0 = no max)">;
+ HelpText<"Limit to maximum N allocation tokens (0 = target SIZE_MAX)">;
def falloc_token_mode_EQ : Joined<["-"], "falloc-token-mode=">,
Group<f_Group>, Visibility<[CC1Option]>,
diff --git a/clang/lib/AST/ByteCode/InterpBuiltin.cpp b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
index 5a96320e12b6f..b6013834b6852 100644
--- a/clang/lib/AST/ByteCode/InterpBuiltin.cpp
+++ b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
@@ -1317,8 +1317,9 @@ static bool interp__builtin_infer_alloc_token(InterpState &S, CodePtr OpPC,
uint64_t BitWidth = ASTCtx.getTypeSize(ASTCtx.getSizeType());
auto Mode =
ASTCtx.getLangOpts().AllocTokenMode.value_or(llvm::DefaultAllocTokenMode);
+ auto MaxTokensOpt = ASTCtx.getLangOpts().AllocTokenMax;
uint64_t MaxTokens =
- ASTCtx.getLangOpts().AllocTokenMax.value_or(~0ULL >> (64 - BitWidth));
+ MaxTokensOpt.value_or(0) ? *MaxTokensOpt : (~0ULL >> (64 - BitWidth));
// We do not read any of the arguments; discard them.
for (int I = Call->getNumArgs() - 1; I >= 0; --I)
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 74f6e3acb6b39..120c68d27de13 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -15559,8 +15559,9 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
auto Mode =
Info.getLangOpts().AllocTokenMode.value_or(llvm::DefaultAllocTokenMode);
uint64_t BitWidth = Info.Ctx.getTypeSize(Info.Ctx.getSizeType());
+ auto MaxTokensOpt = Info.getLangOpts().AllocTokenMax;
uint64_t MaxTokens =
- Info.getLangOpts().AllocTokenMax.value_or(~0ULL >> (64 - BitWidth));
+ MaxTokensOpt.value_or(0) ? *MaxTokensOpt : (~0ULL >> (64 - BitWidth));
auto MaybeToken = llvm::getAllocToken(Mode, *ATMD, MaxTokens);
if (!MaybeToken)
return Error(E, diag::note_constexpr_infer_alloc_token_stateful_mode);
diff --git a/clang/test/SemaCXX/alloc-token.cpp b/clang/test/SemaCXX/alloc-token.cpp
index be7acb7d42ef2..518ad7d94eb96 100644
--- a/clang/test/SemaCXX/alloc-token.cpp
+++ b/clang/test/SemaCXX/alloc-token.cpp
@@ -1,4 +1,5 @@
// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++23 -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++23 -fsyntax-only -verify %s -falloc-token-max=0
// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++23 -fsyntax-only -verify %s -fexperimental-new-constant-interpreter
// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++23 -fsyntax-only -verify %s -falloc-token-mode=typehash -DMODE_TYPEHASH
// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++23 -fsyntax-only -verify %s -falloc-token-max=2 -DTOKEN_MAX=2
diff --git a/llvm/lib/Transforms/Instrumentation/AllocToken.cpp b/llvm/lib/Transforms/Instrumentation/AllocToken.cpp
index 8181e4ef1d74f..cf74354cb438f 100644
--- a/llvm/lib/Transforms/Instrumentation/AllocToken.cpp
+++ b/llvm/lib/Transforms/Instrumentation/AllocToken.cpp
@@ -67,9 +67,10 @@ cl::opt<std::string> ClFuncPrefix("alloc-token-prefix",
cl::desc("The allocation function prefix"),
cl::Hidden, cl::init("__alloc_token_"));
-cl::opt<uint64_t> ClMaxTokens("alloc-token-max",
- cl::desc("Maximum number of tokens (0 = no max)"),
- cl::Hidden, cl::init(0));
+cl::opt<uint64_t>
+ ClMaxTokens("alloc-token-max",
+ cl::desc("Maximum number of tokens (0 = target SIZE_MAX)"),
+ cl::Hidden, cl::init(0));
cl::opt<bool>
ClFastABI("alloc-token-fast-abi",
``````````
</details>
https://github.com/llvm/llvm-project/pull/168689
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