[Clang Interpreter] Initial patch for the constexpr interpreter

Summary:
This patch introduces the skeleton of the constexpr interpreter,
capable of evaluating a simple constexpr functions consisting of
if statements. The interpreter is described in more detail in the
RFC. Further patches will add more features.

Reviewers: Bigcheese, jfb, rsmith

Subscribers: bruno, uenoku, ldionne, Tyker, thegameg, tschuett, dexonsmith, mgorny, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D64146

llvm-svn: 370531

1 files changed, 87 insertions, 0 deletions

diff --git a/clang/lib/AST/Interp/Block.cpp b/clang/lib/AST/Interp/Block.cpp
new file mode 100644
index 00000000000..5fc93eb39f4
--- /dev/null
+++ b/clang/lib/AST/Interp/Block.cpp
@@ -0,0 +1,87 @@
+//===--- Block.cpp - Allocated blocks for the interpreter -------*- 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Defines the classes describing allocated blocks.
+//
+//===----------------------------------------------------------------------===//
+
+#include "Block.h"
+#include "Pointer.h"
+
+using namespace clang;
+using namespace clang::interp;
+
+
+
+void Block::addPointer(Pointer *P) {
+  if (IsStatic)
+    return;
+  if (Pointers)
+    Pointers->Prev = P;
+  P->Next = Pointers;
+  P->Prev = nullptr;
+  Pointers = P;
+}
+
+void Block::removePointer(Pointer *P) {
+  if (IsStatic)
+    return;
+  if (Pointers == P)
+    Pointers = P->Next;
+  if (P->Prev)
+    P->Prev->Next = P->Next;
+  if (P->Next)
+    P->Next->Prev = P->Prev;
+}
+
+void Block::cleanup() {
+  if (Pointers == nullptr && IsDead)
+    (reinterpret_cast<DeadBlock *>(this + 1) - 1)->free();
+}
+
+void Block::movePointer(Pointer *From, Pointer *To) {
+  if (IsStatic)
+    return;
+  To->Prev = From->Prev;
+  if (To->Prev)
+    To->Prev->Next = To;
+  To->Next = From->Next;
+  if (To->Next)
+    To->Next->Prev = To;
+  if (Pointers == From)
+    Pointers = To;
+
+  From->Prev = nullptr;
+  From->Next = nullptr;
+}
+
+DeadBlock::DeadBlock(DeadBlock *&Root, Block *Blk)
+    : Root(Root), B(Blk->Desc, Blk->IsStatic, Blk->IsExtern, /*isDead=*/true) {
+  // Add the block to the chain of dead blocks.
+  if (Root)
+    Root->Prev = this;
+
+  Next = Root;
+  Prev = nullptr;
+  Root = this;
+
+  // Transfer pointers.
+  B.Pointers = Blk->Pointers;
+  for (Pointer *P = Blk->Pointers; P; P = P->Next)
+    P->Pointee = &B;
+}
+
+void DeadBlock::free() {
+  if (Prev)
+    Prev->Next = Next;
+  if (Next)
+    Next->Prev = Prev;
+  if (Root == this)
+    Root = Next;
+  ::free(this);
+}