[clang] [clang][Interp] Implement dynamic memory allocation handling (PR #70306)

[Timm Baeder via cfe-commits]

================
@@ -0,0 +1,91 @@
+//==---- DynamicAllocator.cpp - Types for the constexpr VM -------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "DynamicAllocator.h"
+#include "InterpBlock.h"
+#include "InterpState.h"
+
+using namespace clang;
+using namespace clang::interp;
+
+Block *DynamicAllocator::allocate(const Expr *Source, PrimType T,
+                                  size_t NumElements) {
+  assert(NumElements > 0);
+  // Create a new descriptor for an array of the specified size and
+  // element type.
+  const Descriptor *D = allocateDescriptor(
+      Source, T, Descriptor::InlineDescMD, NumElements, /*IsConst=*/false,
+      /*IsTemporary=*/false, /*IsMutable=*/false);
+  return allocate(D);
+}
+
+Block *DynamicAllocator::allocate(const Descriptor *ElementDesc,
+                                  size_t NumElements) {
+  assert(NumElements > 0);
+  // Create a new descriptor for an array of the specified size and
+  // element type.
+  const Descriptor *D = allocateDescriptor(
+      ElementDesc->asExpr(), ElementDesc, Descriptor::InlineDescMD, NumElements,
+      /*IsConst=*/false, /*IsTemporary=*/false, /*IsMutable=*/false);
+  return allocate(D);
+}
+
+Block *DynamicAllocator::allocate(const Descriptor *D) {
+  assert(D->asExpr());
+
+  auto Memory =
+      std::make_unique<std::byte[]>(sizeof(Block) + D->getAllocSize());
+  auto *B = new (Memory.get()) Block(D, /*isStatic=*/false);
+  B->invokeCtor();
+
+  InlineDescriptor *ID = reinterpret_cast<InlineDescriptor *>(B->rawData());
+  ID->Desc = const_cast<Descriptor *>(D);
+  ID->IsActive = true;
+  ID->Offset = sizeof(InlineDescriptor);
+  ID->IsBase = false;
+  ID->IsFieldMutable = false;
+  ID->IsConst = false;
+  ID->IsInitialized = false;
+  assert(ID->Desc);
+
+  if (auto It = AllocationSites.find(D->asExpr()); It != AllocationSites.end())
+    It->second.Allocations.emplace_back(std::move(Memory));
+  else
+    AllocationSites.insert(
+        {D->asExpr(), AllocationSite(std::move(Memory), D->isArray())});
+  return B;
+}
+
+void DynamicAllocator::deallocate(const Expr *Source,
+                                  const Block *BlockToDelete, InterpState &S) {
+  assert(AllocationSites.contains(Source));
+
+  auto It = AllocationSites.find(Source);
+  assert(It != AllocationSites.end());
+
+  auto &Site = It->second;
+  assert(Site.size() > 0);
+
+  // Find the Block to delete.
+  size_t I = 0;
+  [[maybe_unused]] bool Found = false;
+  for (auto &A : Site.Allocations) {
+    Block *B = reinterpret_cast<Block *>(A.Memory.get());
+    if (B == BlockToDelete) {
+      S.deallocate(B);
+      B->invokeDtor();
+      Site.Allocations.erase(Site.Allocations.begin() + I);
----------------
tbaederr wrote:

> I is never incremented.

lol, nice testing on my side.

https://github.com/llvm/llvm-project/pull/70306