[clang] Introduce intra-procedural lifetime analysis in Clang (PR #142313)

[Gábor Horváth via cfe-commits]

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@@ -0,0 +1,728 @@
+#include "clang/Analysis/Analyses/LifetimeSafety.h"
+#include "clang/AST/Decl.h"
+#include "clang/AST/Expr.h"
+#include "clang/AST/StmtVisitor.h"
+#include "clang/AST/Type.h"
+#include "clang/Analysis/AnalysisDeclContext.h"
+#include "clang/Analysis/CFG.h"
+#include "clang/Analysis/FlowSensitive/DataflowWorklist.h"
+#include "llvm/ADT/ImmutableMap.h"
+#include "llvm/ADT/ImmutableSet.h"
+#include "llvm/ADT/PointerUnion.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/TimeProfiler.h"
+#include <vector>
+
+namespace clang {
+namespace {
+
+struct Point {
+  const clang::CFGBlock *Block;
+  /// Index into Block->Elements().
+  unsigned ElementIndex;
+
+  Point(const clang::CFGBlock *B = nullptr, unsigned Idx = 0)
+      : Block(B), ElementIndex(Idx) {}
+
+  bool operator==(const Point &Other) const {
+    return Block == Other.Block && ElementIndex == Other.ElementIndex;
+  }
+};
+
+/// Represents the storage location being borrowed, e.g., a specific stack
+/// variable.
+/// TODO: Handle member accesseslike `s.y`.
+struct Path {
+  const clang::ValueDecl *D;
+
+  enum class Kind : uint8_t {
----------------
Xazax-hun wrote:

> Each of the entities like stack variable, temporaries, fields (of stack variables) would need to be handled slightly differently and this is only where this PathKind would be used.

I am not yet convinced that we will actually need this, but this may be because we only have one kind implemented so far:

```
      if (LoanPath.PathKind == AccessPath::Kind::StackVariable) {
         if (LoanPath.D == DestructedVD) {
```

Here, I'd imagine when we issue the ExpireLoan, we know exactly what kind of entity is expiring. The AST/CFG should tell us if it was a stack variable, a heap location, or a temporary. After that, I'd expect that the `AccessPath` should have all the information we need to check what Loans should expire here (e.g., the fields of an expired loan should also expire). 

https://github.com/llvm/llvm-project/pull/142313