[llvm] [FunctionAttrs] Add the "initializes" attribute inference (PR #97373)

[Haopeng Liu via llvm-commits]

================
@@ -580,6 +582,206 @@ struct ArgumentUsesTracker : public CaptureTracker {
   const SCCNodeSet &SCCNodes;
 };
 
+// A struct of argument use: a Use and the offset it accesses. This struct
+// is to track uses inside function via GEP. If GEP has a non-constant index,
+// the Offset field is nullopt.
+struct ArgumentUse {
+  Use *U;
+  std::optional<int64_t> Offset;
+};
+
+// A struct of argument access info. "Unknown" accesses are the cases like
+// unrecognized instructions, instructions that have more than one use of
+// the argument, or volatile memory accesses. "Unknown" implies "IsClobber"
+// and an empty access range.
+// Write or Read accesses can be clobbers as well for example, a Load with
+// scalable type.
+struct ArgumentAccessInfo {
+  enum class AccessType : uint8_t { Write, Read, Unknown };
+  AccessType ArgAccessType;
+  bool IsClobber = false;
+  ConstantRangeList AccessRanges;
+};
+
+// A struct to wrap the argument use info per block.
+struct UsesPerBlockInfo {
+  SmallDenseMap<Instruction *, ArgumentAccessInfo, 4> Insts;
+  bool HasWrites = false;
+  bool HasClobber = false;
+};
+
+// A struct to summarize the argument use info in a function.
+struct ArgumentUsesSummary {
+  bool HasAnyWrite = false;
+  bool HasWriteOutsideEntryBB = false;
+  SmallDenseMap<const BasicBlock *, UsesPerBlockInfo, 16> UsesPerBlock;
+};
+
+ArgumentAccessInfo GetArgmentAccessInfo(const Instruction *I,
+                                        const ArgumentUse &ArgUse,
+                                        const DataLayout &DL) {
+  auto GetTypeAccessRange =
+      [&DL](Type *Ty,
+            std::optional<int64_t> Offset) -> std::optional<ConstantRange> {
+    auto TypeSize = DL.getTypeStoreSize(Ty);
+    if (!TypeSize.isScalable() && Offset) {
+      int64_t Size = TypeSize.getFixedValue();
+      return ConstantRange(APInt(64, *Offset, true),
+                           APInt(64, *Offset + Size, true));
+    }
+    return std::nullopt;
+  };
+  auto GetConstantIntRange =
+      [](Value *Length,
+         std::optional<int64_t> Offset) -> std::optional<ConstantRange> {
+    auto *ConstantLength = dyn_cast<ConstantInt>(Length);
+    if (ConstantLength && Offset)
+      return ConstantRange(
+          APInt(64, *Offset, true),
+          APInt(64, *Offset + ConstantLength->getSExtValue(), true));
+    return std::nullopt;
+  };
+  if (auto *SI = dyn_cast<StoreInst>(I)) {
+    if (!SI->isVolatile() && &SI->getOperandUse(1) == ArgUse.U) {
+      // Get the fixed type size of "SI". Since the access range of a write
+      // will be unioned, if "SI" doesn't have a fixed type size, we just set
+      // the access range to empty.
+      ConstantRangeList AccessRanges;
+      if (auto TypeAccessRange =
+              GetTypeAccessRange(SI->getAccessType(), ArgUse.Offset))
+        AccessRanges.insert(*TypeAccessRange);
+      return {ArgumentAccessInfo::AccessType::Write,
+              /*IsClobber=*/false, AccessRanges};
+    }
+  } else if (auto *LI = dyn_cast<LoadInst>(I)) {
+    if (!LI->isVolatile()) {
+      assert(&LI->getOperandUse(0) == ArgUse.U);
+      // Get the fixed type size of "LI". Different from Write, if "LI"
+      // doesn't have a fixed type size, we conservatively set as a clobber
+      // with an empty access range.
+      if (auto TypeAccessRange =
+              GetTypeAccessRange(LI->getAccessType(), ArgUse.Offset))
+        return {ArgumentAccessInfo::AccessType::Read,
+                /*IsClobber=*/false,
+                {*TypeAccessRange}};
+      return {ArgumentAccessInfo::AccessType::Read, /*IsClobber=*/true, {}};
+    }
+  } else if (auto *MemSet = dyn_cast<MemSetInst>(I)) {
+    if (!MemSet->isVolatile()) {
+      ConstantRangeList AccessRanges;
+      if (auto AccessRange =
+              GetConstantIntRange(MemSet->getLength(), ArgUse.Offset))
+        AccessRanges.insert(*AccessRange);
+      return {ArgumentAccessInfo::AccessType::Write,
+              /*IsClobber=*/false, AccessRanges};
+    }
+  } else if (auto *MTI = dyn_cast<MemTransferInst>(I)) {
+    if (!MTI->isVolatile()) {
+      if (&MTI->getOperandUse(0) == ArgUse.U) {
+        ConstantRangeList AccessRanges;
+        if (auto AccessRange =
+                GetConstantIntRange(MTI->getLength(), ArgUse.Offset))
+          AccessRanges.insert(*AccessRange);
+        return {ArgumentAccessInfo::AccessType::Write,
+                /*IsClobber=*/false, AccessRanges};
+      } else if (&MTI->getOperandUse(1) == ArgUse.U) {
+        if (auto AccessRange =
+                GetConstantIntRange(MTI->getLength(), ArgUse.Offset))
+          return {ArgumentAccessInfo::AccessType::Read,
+                  /*IsClobber=*/false,
+                  {*AccessRange}};
+        return {ArgumentAccessInfo::AccessType::Read, /*IsClobber=*/true, {}};
+      }
+    }
+  } else if (auto *CB = dyn_cast<CallBase>(I)) {
+    if (CB->isArgOperand(ArgUse.U)) {
+      unsigned ArgNo = CB->getArgOperandNo(ArgUse.U);
+      bool IsInitialize = CB->paramHasAttr(ArgNo, Attribute::Initializes);
+      // Argument is only not clobbered when parameter is writeonly/readnone
+      // and nocapture.
+      bool IsClobber = !(CB->onlyWritesMemory(ArgNo) &&
+                         CB->paramHasAttr(ArgNo, Attribute::NoCapture));
+      ConstantRangeList AccessRanges;
+      if (IsInitialize && ArgUse.Offset) {
+        Attribute Attr = CB->getParamAttr(ArgNo, Attribute::Initializes);
+        ConstantRangeList CBCRL = Attr.getValueAsConstantRangeList();
+        for (ConstantRange &CR : CBCRL)
+          AccessRanges.insert(ConstantRange(CR.getLower() + *ArgUse.Offset,
+                                            CR.getUpper() + *ArgUse.Offset));
+        return {ArgumentAccessInfo::AccessType::Write, IsClobber, AccessRanges};
+      }
+    }
+  }
+  // Unrecognized instructions are considered clobbers.
+  return {ArgumentAccessInfo::AccessType::Unknown, /*IsClobber=*/true, {}};
+}
+
+// Collect the uses of argument "A" in "F".
+ArgumentUsesSummary CollectArgumentUsesPerBlock(Argument &A, Function &F) {
+  auto &DL = F.getParent()->getDataLayout();
+  auto PointerSize =
+      DL.getIndexSizeInBits(A.getType()->getPointerAddressSpace());
+  ArgumentUsesSummary Result;
+
+  BasicBlock &EntryBB = F.getEntryBlock();
+  SmallVector<ArgumentUse, 4> Worklist;
+  for (Use &U : A.uses())
+    Worklist.push_back({&U, 0});
+
+  // Update "UsesPerBlock" with the block of "I" as key and "Info" as value.
+  // Return true if the block of "I" has write accesses after updating.
+  auto UpdateUseInfo = [&Result](Instruction *I, ArgumentAccessInfo Info) {
+    auto *BB = I->getParent();
+    auto &BBInfo = Result.UsesPerBlock.getOrInsertDefault(BB);
+    bool AlreadyVisitedInst = BBInfo.Insts.contains(I);
+    auto &IInfo = BBInfo.Insts[I];
+
+    // Instructions that have more than one use of the argument are considered
+    // as clobbers.
+    if (AlreadyVisitedInst) {
+      IInfo = {ArgumentAccessInfo::AccessType::Unknown, /*IsClobber=*/true, {}};
+      BBInfo.HasClobber = true;
+      return false;
+    }
+
+    IInfo = Info;
----------------
haopliu wrote:

Done.

https://github.com/llvm/llvm-project/pull/97373