[llvm] [Attributor] New attribute to identify what byte ranges are alive for an allocation (PR #66148)

[Johannes Doerfert via llvm-commits]

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@@ -12658,6 +12665,232 @@ struct AAAddressSpaceCallSiteArgument final : AAAddressSpaceImpl {
 };
 } // namespace
 
+/// ----------- Allocation Info ----------
+namespace {
+struct AAAllocationInfoImpl : public AAAllocationInfo {
+  AAAllocationInfoImpl(const IRPosition &IRP, Attributor &A)
+      : AAAllocationInfo(IRP, A) {}
+
+  std::optional<TypeSize> getAllocatedSize() const override {
+    assert(isValidState() && "the AA is invalid");
+    return AssumedAllocatedSize;
+  }
+
+  ChangeStatus updateImpl(Attributor &A) override {
+
+    const IRPosition &IRP = getIRPosition();
+    Instruction *I = IRP.getCtxI();
+
+    /*TODO: update check for malloc like calls.*/
+    if (!isa<AllocaInst>(I))
+      return indicatePessimisticFixpoint();
+
+    bool IsKnownNoCapture;
+    if (!AA::hasAssumedIRAttr<Attribute::NoCapture>(
+            A, this, IRP, DepClassTy::OPTIONAL, IsKnownNoCapture))
+      return indicatePessimisticFixpoint();
+
+    if (IsKnownNoCapture)
+      return indicatePessimisticFixpoint();
+
+    const AAPointerInfo *PI =
+        A.getOrCreateAAFor<AAPointerInfo>(IRP, *this, DepClassTy::REQUIRED);
+
+    if (!PI)
+      return indicatePessimisticFixpoint();
+
+    if (!PI->getState().isValidState())
+      return indicatePessimisticFixpoint();
+
+    const DataLayout &DL = A.getDataLayout();
+    int64_t BinSize = PI->numOffsetBins();
+    switch (BinSize) {
+    case 0: {
+      switch (I->getOpcode()) {
+      /*TODO: add case for malloc like calls*/
+      case Instruction::Alloca: {
+        AllocaInst *AI = cast<AllocaInst>(I);
+        const auto AllocationSize = AI->getAllocationSize(DL);
+
+        if (!AllocationSize || *AllocationSize == 0)
+          return indicatePessimisticFixpoint();
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jdoerfert wrote:

This is now checked twice. I'm not sure why we need it in the first place, but if we do, why not check it at the very beginning once?

https://github.com/llvm/llvm-project/pull/66148