[AMDGPU][Backend] Fix user-after-free in AMDGPUReleaseVGPRs::isLastVG…

…PRUseVMEMStore

Reviewed By: jpages, arsenm

Differential Revision: https://reviews.llvm.org/D134641

llvm/lib/Target/AMDGPU/AMDGPUReleaseVGPRs.cpp

@@ -16,7 +16,7 @@
 #include "GCNSubtarget.h"
 #include "MCTargetDesc/AMDGPUMCTargetDesc.h"
 #include "SIDefines.h"
-#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/DepthFirstIterator.h"
 #include "llvm/CodeGen/MachineBasicBlock.h"
 #include "llvm/CodeGen/MachineOperand.h"
 using namespace llvm;
@@ -29,60 +29,76 @@ class AMDGPUReleaseVGPRs : public MachineFunctionPass {
 public:
   static char ID;
 
-  const SIInstrInfo *SII;
-  const SIRegisterInfo *TRI;
-
   AMDGPUReleaseVGPRs() : MachineFunctionPass(ID) {}
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.setPreservesAll();
     MachineFunctionPass::getAnalysisUsage(AU);
   }
 
-  // Used to cache the result of isLastInstructionVMEMStore for each block
-  using BlockVMEMStoreType = DenseMap<MachineBasicBlock *, bool>;
-  BlockVMEMStoreType BlockVMEMStore;
-
-  // Return true if the last instruction referencing a vgpr in this MBB
-  // is a VMEM store, otherwise return false.
-  // Visit previous basic blocks to find this last instruction if needed.
-  // Because this pass is late in the pipeline, it is expected that the
+  // Track if the last instruction referencing a vgpr in a MBB is a VMEM
+  // store. Because this pass is late in the pipeline, it is expected that the
   // last vgpr use will likely be one of vmem store, ds, exp.
   // Loads and others vgpr operations would have been
   // deleted by this point, except for complex control flow involving loops.
   // This is why we are just testing the type of instructions rather
   // than the operands.
-  bool isLastVGPRUseVMEMStore(MachineBasicBlock &MBB) {
-    // Use the cache to break infinite loop and save some time. Initialize to
-    // false in case we have a cycle.
-    BlockVMEMStoreType::iterator It;
-    bool Inserted;
-    std::tie(It, Inserted) = BlockVMEMStore.insert({&MBB, false});
-    bool &CacheEntry = It->second;
-    if (!Inserted)
-      return CacheEntry;
-
-    for (auto &MI : reverse(MBB.instrs())) {
-      // If it's a VMEM store, a vgpr will be used, return true.
-      if ((SIInstrInfo::isVMEM(MI) || SIInstrInfo::isFLAT(MI)) && MI.mayStore())
-        return CacheEntry = true;
-
-      // If it's referencing a VGPR but is not a VMEM store, return false.
-      if (SIInstrInfo::isDS(MI) || SIInstrInfo::isEXP(MI) ||
-          SIInstrInfo::isVMEM(MI) || SIInstrInfo::isFLAT(MI) ||
-          SIInstrInfo::isVALU(MI))
-        return CacheEntry = false;
+  class LastVGPRUseIsVMEMStore {
+    BitVector BlockVMEMStore;
+
+    static Optional<bool> lastVGPRUseIsStore(const MachineBasicBlock &MBB) {
+      for (auto &MI : reverse(MBB.instrs())) {
+        // If it's a VMEM store, a VGPR will be used, return true.
+        if ((SIInstrInfo::isVMEM(MI) || SIInstrInfo::isFLAT(MI)) &&
+            MI.mayStore())
+          return true;
+
+        // If it's referencing a VGPR but is not a VMEM store, return false.
+        if (SIInstrInfo::isDS(MI) || SIInstrInfo::isEXP(MI) ||
+            SIInstrInfo::isVMEM(MI) || SIInstrInfo::isFLAT(MI) ||
+            SIInstrInfo::isVALU(MI))
+          return false;
+      }
+      // Wait until the values are propagated from the predecessors
+      return None;
     }
 
-    // Recursive call into parent blocks. Look into predecessors if there is no
-    // vgpr used in this block.
-    return CacheEntry = llvm::any_of(MBB.predecessors(),
-                                     [this](MachineBasicBlock *Parent) {
-                                       return isLastVGPRUseVMEMStore(*Parent);
-                                     });
-  }
+  public:
+    LastVGPRUseIsVMEMStore(const MachineFunction &MF)
+        : BlockVMEMStore(MF.getNumBlockIDs()) {
+
+      df_iterator_default_set<const MachineBasicBlock *> Visited;
+      SmallVector<const MachineBasicBlock *> EndWithVMEMStoreBlocks;
+
+      for (const auto &MBB : MF) {
+        auto LastUseIsStore = lastVGPRUseIsStore(MBB);
+        if (!LastUseIsStore.has_value())
+          continue;
+
+        if (*LastUseIsStore) {
+          EndWithVMEMStoreBlocks.push_back(&MBB);
+        } else {
+          Visited.insert(&MBB);
+        }
+      }
+
+      for (const auto *MBB : EndWithVMEMStoreBlocks) {
+        for (const auto *Succ : depth_first_ext(MBB, Visited)) {
+          BlockVMEMStore[Succ->getNumber()] = true;
+        }
+      }
+    }
+
+    // Return true if the last instruction referencing a vgpr in this MBB
+    // is a VMEM store, otherwise return false.
+    bool isLastVGPRUseVMEMStore(const MachineBasicBlock &MBB) const {
+      return BlockVMEMStore[MBB.getNumber()];
+    }
+  };
 
-  bool runOnMachineBasicBlock(MachineBasicBlock &MBB) {
+  static bool
+  runOnMachineBasicBlock(MachineBasicBlock &MBB, const SIInstrInfo *SII,
+                         const LastVGPRUseIsVMEMStore &BlockVMEMStore) {
 
     bool Changed = false;
 
@@ -93,7 +109,7 @@ class AMDGPUReleaseVGPRs : public MachineFunctionPass {
         // If the last instruction using a VGPR in the block is a VMEM store,
         // release VGPRs. The VGPRs release will be placed just before ending
         // the program
-        if (isLastVGPRUseVMEMStore(MBB)) {
+        if (BlockVMEMStore.isLastVGPRUseVMEMStore(MBB)) {
           BuildMI(MBB, MI, DebugLoc(), SII->get(AMDGPU::S_SENDMSG))
               .addImm(AMDGPU::SendMsg::ID_DEALLOC_VGPRS_GFX11Plus);
           Changed = true;
@@ -117,16 +133,14 @@ class AMDGPUReleaseVGPRs : public MachineFunctionPass {
     LLVM_DEBUG(dbgs() << "AMDGPUReleaseVGPRs running on " << MF.getName()
                       << "\n");
 
-    SII = ST.getInstrInfo();
-    TRI = ST.getRegisterInfo();
+    const SIInstrInfo *SII = ST.getInstrInfo();
+    LastVGPRUseIsVMEMStore BlockVMEMStore(MF);
 
     bool Changed = false;
     for (auto &MBB : MF) {
-      Changed |= runOnMachineBasicBlock(MBB);
+      Changed |= runOnMachineBasicBlock(MBB, SII, BlockVMEMStore);
     }
 
-    BlockVMEMStore.clear();
-
     return Changed;
   }
 };