[Clang] Implement constexpr evaluation for __builtin_infer_alloc_token()

clang/docs/AllocToken.rst

@@ -37,8 +37,8 @@ The default mode to calculate tokens is:
   pointers.
 
 Other token ID assignment modes are supported, but they may be subject to
-change or removal. These may (experimentally) be selected with ``-mllvm
--alloc-token-mode=<mode>``:
+change or removal. These may (experimentally) be selected with ``-Xclang
+-falloc-token-mode=<mode>``:
 
 * ``typehash``: This mode assigns a token ID based on the hash of the allocated
   type's name.

clang/include/clang/AST/InferAlloc.h

@@ -0,0 +1,35 @@
+//===--- InferAlloc.h - Allocation type inference ---------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines interfaces for allocation-related type inference.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_AST_INFERALLOC_H
+#define LLVM_CLANG_AST_INFERALLOC_H
+
+#include "clang/AST/ASTContext.h"
+#include "clang/AST/Expr.h"
+#include "llvm/Support/AllocToken.h"
+#include <optional>
+
+namespace clang {
+namespace infer_alloc {
+
+/// Infer the possible allocated type from an allocation call expression.
+QualType inferPossibleType(const CallExpr *E, const ASTContext &Ctx,
+                           const CastExpr *CastE);
+
+/// Get the information required for construction of an allocation token ID.
+std::optional<llvm::AllocTokenMetadata>
+getAllocTokenMetadata(QualType T, const ASTContext &Ctx);
+
+} // namespace infer_alloc
+} // namespace clang
+
+#endif // LLVM_CLANG_AST_INFERALLOC_H

clang/include/clang/Basic/Builtins.td

@@ -4727,6 +4727,13 @@ def PtrauthStringDiscriminator : Builtin {
   let Prototype = "size_t(char const*)";
 }
 
+// AllocToken builtins.
+def InferAllocToken : Builtin {
+  let Spellings = ["__builtin_infer_alloc_token"];
+  let Attributes = [NoThrow, Const, Pure, CustomTypeChecking, Constexpr, UnevaluatedArguments];
+  let Prototype = "size_t(...)";
+}
+
 // OpenCL v2.0 s6.13.16, s9.17.3.5 - Pipe functions.
 // We need the generic prototype, since the packet type could be anything.
 def ReadPipe : OCLPipeLangBuiltin {

clang/include/clang/Basic/CodeGenOptions.h

@@ -447,10 +447,6 @@ class CodeGenOptions : public CodeGenOptionsBase {
 
   std::optional<double> AllowRuntimeCheckSkipHotCutoff;
 
-  /// Maximum number of allocation tokens (0 = no max), nullopt if none set (use
-  /// pass default).
-  std::optional<uint64_t> AllocTokenMax;
-
   /// List of backend command-line options for -fembed-bitcode.
   std::vector<uint8_t> CmdArgs;
 

clang/include/clang/Basic/DiagnosticASTKinds.td

@@ -403,6 +403,12 @@ def note_constexpr_assumption_failed : Note<
 def note_constexpr_countzeroes_zero : Note<
   "evaluation of %select{__builtin_elementwise_clzg|__builtin_elementwise_ctzg}0 "
   "with a zero value is undefined">;
+def note_constexpr_infer_alloc_token_type_inference_failed : Note<
+  "could not infer allocation type for __builtin_infer_alloc_token">;
+def note_constexpr_infer_alloc_token_no_metadata : Note<
+  "could not get token metadata for inferred type">;
+def note_constexpr_infer_alloc_token_stateful_mode : Note<
+  "stateful alloc token mode not supported in constexpr">;
 def err_experimental_clang_interp_failed : Error<
   "the experimental clang interpreter failed to evaluate an expression">;
 

clang/include/clang/Basic/LangOptions.h

@@ -25,6 +25,7 @@
 #include "llvm/ADT/FloatingPointMode.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/BinaryFormat/DXContainer.h"
+#include "llvm/Support/AllocToken.h"
 #include "llvm/TargetParser/Triple.h"
 #include <optional>
 #include <string>
@@ -565,6 +566,13 @@ 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).
+  std::optional<uint64_t> AllocTokenMax;
+
+  /// The allocation token mode.
+  std::optional<llvm::AllocTokenMode> AllocTokenMode;
+
   LangOptions();
 
   /// Set language defaults for the given input language and

clang/include/clang/Driver/Options.td

@@ -2751,6 +2751,10 @@ def falloc_token_max_EQ : Joined<["-"], "falloc-token-max=">,
   MetaVarName<"<N>">,
   HelpText<"Limit to maximum N allocation tokens (0 = no max)">;
 
+def falloc_token_mode_EQ : Joined<["-"], "falloc-token-mode=">,
+  Group<f_Group>, Visibility<[CC1Option]>,
+  HelpText<"Set the allocation token mode (experimental)">;
+
 def fallow_runtime_check_skip_hot_cutoff_EQ
     : Joined<["-"], "fallow-runtime-check-skip-hot-cutoff=">,
       Group<f_clang_Group>,

clang/lib/AST/ByteCode/InterpBuiltin.cpp

@@ -11,12 +11,14 @@
 #include "Interp.h"
 #include "InterpBuiltinBitCast.h"
 #include "PrimType.h"
+#include "clang/AST/InferAlloc.h"
 #include "clang/AST/OSLog.h"
 #include "clang/AST/RecordLayout.h"
 #include "clang/Basic/Builtins.h"
 #include "clang/Basic/TargetBuiltins.h"
 #include "clang/Basic/TargetInfo.h"
 #include "llvm/ADT/StringExtras.h"
+#include "llvm/Support/AllocToken.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/SipHash.h"
 
@@ -1306,6 +1308,45 @@ interp__builtin_ptrauth_string_discriminator(InterpState &S, CodePtr OpPC,
   return true;
 }
 
+static bool interp__builtin_infer_alloc_token(InterpState &S, CodePtr OpPC,
+                                              const InterpFrame *Frame,
+                                              const CallExpr *Call) {
+  const ASTContext &ASTCtx = S.getASTContext();
+  uint64_t BitWidth = ASTCtx.getTypeSize(ASTCtx.getSizeType());
+  auto Mode =
+      ASTCtx.getLangOpts().AllocTokenMode.value_or(llvm::DefaultAllocTokenMode);
+  uint64_t MaxTokens =
+      ASTCtx.getLangOpts().AllocTokenMax.value_or(~0ULL >> (64 - BitWidth));
+
+  // We do not read any of the arguments; discard them.
+  for (int I = Call->getNumArgs() - 1; I >= 0; --I)
+    discard(S.Stk, *S.getContext().classify(Call->getArg(I)));
+
+  // Note: Type inference from a surrounding cast is not supported in
+  // constexpr evaluation.
+  QualType AllocType = infer_alloc::inferPossibleType(Call, ASTCtx, nullptr);
+  if (AllocType.isNull()) {
+    S.CCEDiag(Call,
+              diag::note_constexpr_infer_alloc_token_type_inference_failed);
+    return false;
+  }
+
+  auto ATMD = infer_alloc::getAllocTokenMetadata(AllocType, ASTCtx);
+  if (!ATMD) {
+    S.CCEDiag(Call, diag::note_constexpr_infer_alloc_token_no_metadata);
+    return false;
+  }
+
+  auto MaybeToken = llvm::getAllocToken(Mode, *ATMD, MaxTokens);
+  if (!MaybeToken) {
+    S.CCEDiag(Call, diag::note_constexpr_infer_alloc_token_stateful_mode);
+    return false;
+  }
+
+  pushInteger(S, llvm::APInt(BitWidth, *MaybeToken), ASTCtx.getSizeType());
+  return true;
+}
+
 static bool interp__builtin_operator_new(InterpState &S, CodePtr OpPC,
                                          const InterpFrame *Frame,
                                          const CallExpr *Call) {
@@ -3489,6 +3530,9 @@ bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const CallExpr *Call,
   case Builtin::BI__builtin_ptrauth_string_discriminator:
     return interp__builtin_ptrauth_string_discriminator(S, OpPC, Frame, Call);
 
+  case Builtin::BI__builtin_infer_alloc_token:
+    return interp__builtin_infer_alloc_token(S, OpPC, Frame, Call);
+
   case Builtin::BI__noop:
     pushInteger(S, 0, Call->getType());
     return true;

clang/lib/AST/CMakeLists.txt

@@ -66,6 +66,7 @@ add_clang_library(clangAST
   ExternalASTMerger.cpp
   ExternalASTSource.cpp
   FormatString.cpp
+  InferAlloc.cpp
   InheritViz.cpp
   ByteCode/BitcastBuffer.cpp
   ByteCode/ByteCodeEmitter.cpp

clang/lib/AST/ExprConstant.cpp

@@ -44,6 +44,7 @@
 #include "clang/AST/CharUnits.h"
 #include "clang/AST/CurrentSourceLocExprScope.h"
 #include "clang/AST/Expr.h"
+#include "clang/AST/InferAlloc.h"
 #include "clang/AST/OSLog.h"
 #include "clang/AST/OptionalDiagnostic.h"
 #include "clang/AST/RecordLayout.h"
@@ -14415,6 +14416,27 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
     return Success(Result, E);
   }
 
+  case Builtin::BI__builtin_infer_alloc_token: {
+    // If we fail to infer a type, this fails to be a constant expression; this
+    // can be checked with __builtin_constant_p(...).
+    QualType AllocType = infer_alloc::inferPossibleType(E, Info.Ctx, nullptr);
+    if (AllocType.isNull())
+      return Error(
+          E, diag::note_constexpr_infer_alloc_token_type_inference_failed);
+    auto ATMD = infer_alloc::getAllocTokenMetadata(AllocType, Info.Ctx);
+    if (!ATMD)
+      return Error(E, diag::note_constexpr_infer_alloc_token_no_metadata);
+    auto Mode =
+        Info.getLangOpts().AllocTokenMode.value_or(llvm::DefaultAllocTokenMode);
+    uint64_t BitWidth = Info.Ctx.getTypeSize(Info.Ctx.getSizeType());
+    uint64_t MaxTokens =
+        Info.getLangOpts().AllocTokenMax.value_or(~0ULL >> (64 - BitWidth));
+    auto MaybeToken = llvm::getAllocToken(Mode, *ATMD, MaxTokens);
+    if (!MaybeToken)
+      return Error(E, diag::note_constexpr_infer_alloc_token_stateful_mode);
+    return Success(llvm::APInt(BitWidth, *MaybeToken), E);
+  }
+
   case Builtin::BI__builtin_ffs:
   case Builtin::BI__builtin_ffsl:
   case Builtin::BI__builtin_ffsll: {