[InstCombine] Iterative replacement in PtrReplacer (llvm#145410) (llvm#2803)

gandhi56 · web-flow · commit 55f615ed85bf · 2025-07-02T12:20:38.000-04:00
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -244,11 +244,10 @@ class PointerReplacer {
   void replacePointer(Value *V);
 
 private:
-  bool collectUsersRecursive(Instruction &I);
   void replace(Instruction *I);
-  Value *getReplacement(Value *I);
+  Value *getReplacement(Value *V) const { return WorkMap.lookup(V); }
   bool isAvailable(Instruction *I) const {
-    return I == &Root || Worklist.contains(I);
+    return I == &Root || UsersToReplace.contains(I);
   }
 
   bool isEqualOrValidAddrSpaceCast(const Instruction *I,
@@ -260,8 +259,7 @@ class PointerReplacer {
     return (FromAS == ToAS) || IC.isValidAddrSpaceCast(FromAS, ToAS);
   }
 
-  SmallPtrSet<Instruction *, 32> ValuesToRevisit;
-  SmallSetVector<Instruction *, 4> Worklist;
+  SmallSetVector<Instruction *, 32> UsersToReplace;
   MapVector<Value *, Value *> WorkMap;
   InstCombinerImpl &IC;
   Instruction &Root;
@@ -270,80 +268,119 @@ class PointerReplacer {
 } // end anonymous namespace
 
 bool PointerReplacer::collectUsers() {
-  if (!collectUsersRecursive(Root))
-    return false;
-
-  // Ensure that all outstanding (indirect) users of I
-  // are inserted into the Worklist. Return false
-  // otherwise.
-  return llvm::set_is_subset(ValuesToRevisit, Worklist);
-}
+  SmallVector<Instruction *> Worklist;
+  SmallSetVector<Instruction *, 32> ValuesToRevisit;
+
+  auto PushUsersToWorklist = [&](Instruction *Inst) {
+    for (auto *U : Inst->users())
+      if (auto *I = dyn_cast<Instruction>(U))
+        if (!isAvailable(I) && !ValuesToRevisit.contains(I))
+          Worklist.emplace_back(I);
+  };
 
-bool PointerReplacer::collectUsersRecursive(Instruction &I) {
-  for (auto *U : I.users()) {
-    auto *Inst = cast<Instruction>(&*U);
+  PushUsersToWorklist(&Root);
+  while (!Worklist.empty()) {
+    Instruction *Inst = Worklist.pop_back_val();
     if (auto *Load = dyn_cast<LoadInst>(Inst)) {
       if (Load->isVolatile())
         return false;
-      Worklist.insert(Load);
+      UsersToReplace.insert(Load);
     } else if (auto *PHI = dyn_cast<PHINode>(Inst)) {
-      // All incoming values must be instructions for replacability
-      if (any_of(PHI->incoming_values(),
-                 [](Value *V) { return !isa<Instruction>(V); }))
-        return false;
-
-      // If at least one incoming value of the PHI is not in Worklist,
-      // store the PHI for revisiting and skip this iteration of the
-      // loop.
-      if (any_of(PHI->incoming_values(), [this](Value *V) {
-            return !isAvailable(cast<Instruction>(V));
+      /// TODO: Handle poison and null pointers for PHI and select.
+      // If all incoming values are available, mark this PHI as
+      // replacable and push it's users into the worklist.
+      bool IsReplaceable = true;
+      if (all_of(PHI->incoming_values(), [&](Value *V) {
+            if (!isa<Instruction>(V))
+              return IsReplaceable = false;
+            return isAvailable(cast<Instruction>(V));
           })) {
-        ValuesToRevisit.insert(Inst);
+        UsersToReplace.insert(PHI);
+        PushUsersToWorklist(PHI);
         continue;
       }
 
-      Worklist.insert(PHI);
-      if (!collectUsersRecursive(*PHI))
-        return false;
-    } else if (auto *SI = dyn_cast<SelectInst>(Inst)) {
-      if (!isa<Instruction>(SI->getTrueValue()) ||
-          !isa<Instruction>(SI->getFalseValue()))
+      // Either an incoming value is not an instruction or not all
+      // incoming values are available. If this PHI was already
+      // visited prior to this iteration, return false.
+      if (!IsReplaceable || !ValuesToRevisit.insert(PHI))
         return false;
 
-      if (!isAvailable(cast<Instruction>(SI->getTrueValue())) ||
-          !isAvailable(cast<Instruction>(SI->getFalseValue()))) {
-        ValuesToRevisit.insert(Inst);
-        continue;
+      // Push PHI back into the stack, followed by unavailable
+      // incoming values.
+      Worklist.emplace_back(PHI);
+      for (unsigned Idx = 0; Idx < PHI->getNumIncomingValues(); ++Idx) {
+        auto *IncomingValue = cast<Instruction>(PHI->getIncomingValue(Idx));
+        if (UsersToReplace.contains(IncomingValue))
+          continue;
+        if (!ValuesToRevisit.insert(IncomingValue))
+          return false;
+        Worklist.emplace_back(IncomingValue);
       }
-      Worklist.insert(SI);
-      if (!collectUsersRecursive(*SI))
-        return false;
-    } else if (isa<GetElementPtrInst>(Inst)) {
-      Worklist.insert(Inst);
-      if (!collectUsersRecursive(*Inst))
+    } else if (auto *SI = dyn_cast<SelectInst>(Inst)) {
+      auto *TrueInst = dyn_cast<Instruction>(SI->getTrueValue());
+      auto *FalseInst = dyn_cast<Instruction>(SI->getFalseValue());
+      if (!TrueInst || !FalseInst)
         return false;
+
+      UsersToReplace.insert(SI);
+      PushUsersToWorklist(SI);
+    } else if (auto *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
+      UsersToReplace.insert(GEP);
+      PushUsersToWorklist(GEP);
     } else if (auto *MI = dyn_cast<MemTransferInst>(Inst)) {
       if (MI->isVolatile())
         return false;
-      Worklist.insert(Inst);
+      UsersToReplace.insert(Inst);
     } else if (isEqualOrValidAddrSpaceCast(Inst, FromAS)) {
-      Worklist.insert(Inst);
-      if (!collectUsersRecursive(*Inst))
-        return false;
+      UsersToReplace.insert(Inst);
+      PushUsersToWorklist(Inst);
     } else if (Inst->isLifetimeStartOrEnd()) {
       continue;
     } else {
       // TODO: For arbitrary uses with address space mismatches, should we check
       // if we can introduce a valid addrspacecast?
-      LLVM_DEBUG(dbgs() << "Cannot handle pointer user: " << *U << '\n');
+      LLVM_DEBUG(dbgs() << "Cannot handle pointer user: " << *Inst << '\n');
       return false;
     }
   }
 
   return true;
 }
 
-Value *PointerReplacer::getReplacement(Value *V) { return WorkMap.lookup(V); }
+void PointerReplacer::replacePointer(Value *V) {
+  assert(cast<PointerType>(Root.getType()) != cast<PointerType>(V->getType()) &&
+         "Invalid usage");
+  WorkMap[&Root] = V;
+  SmallVector<Instruction *> Worklist;
+  SetVector<Instruction *> PostOrderWorklist;
+  SmallPtrSet<Instruction *, 32> Visited;
+
+  // Perform a postorder traversal of the users of Root.
+  Worklist.push_back(&Root);
+  while (!Worklist.empty()) {
+    Instruction *I = Worklist.back();
+
+    // If I has not been processed before, push each of its
+    // replacable users into the worklist.
+    if (Visited.insert(I).second) {
+      for (auto *U : I->users()) {
+        auto *UserInst = cast<Instruction>(U);
+        if (UsersToReplace.contains(UserInst) && !Visited.contains(UserInst))
+          Worklist.push_back(UserInst);
+      }
+      // Otherwise, users of I have already been pushed into
+      // the PostOrderWorklist. Push I as well.
+    } else {
+      PostOrderWorklist.insert(I);
+      Worklist.pop_back();
+    }
+  }
+
+  // Replace pointers in reverse-postorder.
+  for (Instruction *I : reverse(PostOrderWorklist))
+    replace(I);
+}
 
 void PointerReplacer::replace(Instruction *I) {
   if (getReplacement(I))
@@ -365,13 +402,15 @@ void PointerReplacer::replace(Instruction *I) {
     // replacement (new value).
     WorkMap[NewI] = NewI;
   } else if (auto *PHI = dyn_cast<PHINode>(I)) {
-    Type *NewTy = getReplacement(PHI->getIncomingValue(0))->getType();
-    auto *NewPHI = PHINode::Create(NewTy, PHI->getNumIncomingValues(),
-                                   PHI->getName(), PHI->getIterator());
-    for (unsigned int I = 0; I < PHI->getNumIncomingValues(); ++I)
-      NewPHI->addIncoming(getReplacement(PHI->getIncomingValue(I)),
-                          PHI->getIncomingBlock(I));
-    WorkMap[PHI] = NewPHI;
+    // Create a new PHI by replacing any incoming value that is a user of the
+    // root pointer and has a replacement.
+    Value *V = WorkMap.lookup(PHI->getIncomingValue(0));
+    PHI->mutateType(V ? V->getType() : PHI->getIncomingValue(0)->getType());
+    for (unsigned int I = 0; I < PHI->getNumIncomingValues(); ++I) {
+      Value *V = WorkMap.lookup(PHI->getIncomingValue(I));
+      PHI->setIncomingValue(I, V ? V : PHI->getIncomingValue(I));
+    }
+    WorkMap[PHI] = PHI;
   } else if (auto *GEP = dyn_cast<GetElementPtrInst>(I)) {
     auto *V = getReplacement(GEP->getPointerOperand());
     assert(V && "Operand not replaced");
@@ -435,18 +474,6 @@ void PointerReplacer::replace(Instruction *I) {
   }
 }
 
-void PointerReplacer::replacePointer(Value *V) {
-#ifndef NDEBUG
-  auto *PT = cast<PointerType>(Root.getType());
-  auto *NT = cast<PointerType>(V->getType());
-  assert(PT != NT && "Invalid usage");
-#endif
-  WorkMap[&Root] = V;
-
-  for (Instruction *Workitem : Worklist)
-    replace(Workitem);
-}
-
 Instruction *InstCombinerImpl::visitAllocaInst(AllocaInst &AI) {
   if (auto *I = simplifyAllocaArraySize(*this, AI, DT))
     return I;
diff --git a/llvm/test/Transforms/InstCombine/AMDGPU/ptr-replace-alloca.ll b/llvm/test/Transforms/InstCombine/AMDGPU/ptr-replace-alloca.ll
@@ -0,0 +1,79 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -mtriple=amdgcn-amd-amdhsa -passes=instcombine -S < %s | FileCheck %s
+
+%struct.type = type { [256 x <2 x i64>] }
+@g1 = external hidden addrspace(3) global %struct.type, align 16
+
+; This test requires the PtrReplacer to replace users in an RPO traversal.
+; Furthermore, %ptr.else need not to be replaced so it must be retained in
+; %ptr.sink.
+define <2 x i64> @func(ptr addrspace(4) byref(%struct.type) align 16 %0, i1 %cmp.0) {
+; CHECK-LABEL: define <2 x i64> @func(
+; CHECK-SAME: ptr addrspace(4) byref([[STRUCT_TYPE:%.*]]) align 16 [[TMP0:%.*]], i1 [[CMP_0:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    br i1 [[CMP_0]], label %[[IF_THEN:.*]], label %[[IF_ELSE:.*]]
+; CHECK:       [[IF_THEN]]:
+; CHECK-NEXT:    [[VAL_THEN:%.*]] = addrspacecast ptr addrspace(4) [[TMP0]] to ptr
+; CHECK-NEXT:    br label %[[SINK:.*]]
+; CHECK:       [[IF_ELSE]]:
+; CHECK-NEXT:    [[PTR_ELSE:%.*]] = load ptr, ptr addrspace(3) getelementptr inbounds nuw (i8, ptr addrspace(3) @g1, i32 32), align 16
+; CHECK-NEXT:    br label %[[SINK]]
+; CHECK:       [[SINK]]:
+; CHECK-NEXT:    [[PTR_SINK:%.*]] = phi ptr [ [[PTR_ELSE]], %[[IF_ELSE]] ], [ [[VAL_THEN]], %[[IF_THEN]] ]
+; CHECK-NEXT:    [[VAL_SINK:%.*]] = load <2 x i64>, ptr [[PTR_SINK]], align 16
+; CHECK-NEXT:    ret <2 x i64> [[VAL_SINK]]
+;
+entry:
+  %coerce = alloca %struct.type, align 16, addrspace(5)
+  call void @llvm.memcpy.p5.p4.i64(ptr addrspace(5) align 16 %coerce, ptr addrspace(4) align 16 %0, i64 4096, i1 false)
+  br i1 %cmp.0, label %if.then, label %if.else
+
+if.then:                                    ; preds = %entry
+  %ptr.then = getelementptr inbounds i8, ptr addrspace(5) %coerce, i64 0
+  %val.then = addrspacecast ptr addrspace(5) %ptr.then to ptr
+  br label %sink
+
+if.else:                                      ; preds = %entry
+  %ptr.else = load ptr, ptr addrspace(3) getelementptr inbounds nuw (i8, ptr addrspace(3) @g1, i32 32), align 16
+  %val.else = getelementptr inbounds nuw i8, ptr %ptr.else, i64 0
+  br label %sink
+
+sink:
+  %ptr.sink = phi ptr [ %val.else, %if.else ], [ %val.then, %if.then ]
+  %val.sink = load <2 x i64>, ptr %ptr.sink, align 16
+  ret <2 x i64> %val.sink
+}
+
+define <2 x i64> @func_phi_loop(ptr addrspace(4) byref(%struct.type) align 16 %0, i1 %cmp.0) {
+; CHECK-LABEL: define <2 x i64> @func_phi_loop(
+; CHECK-SAME: ptr addrspace(4) byref([[STRUCT_TYPE:%.*]]) align 16 [[TMP0:%.*]], i1 [[CMP_0:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*]]:
+; CHECK-NEXT:    [[VAL_0:%.*]] = addrspacecast ptr addrspace(4) [[TMP0]] to ptr
+; CHECK-NEXT:    br label %[[LOOP:.*]]
+; CHECK:       [[LOOP]]:
+; CHECK-NEXT:    [[PTR_PHI_R:%.*]] = phi ptr [ [[PTR_1:%.*]], %[[LOOP]] ], [ [[VAL_0]], %[[ENTRY]] ]
+; CHECK-NEXT:    [[PTR_1]] = load ptr, ptr addrspace(3) getelementptr inbounds nuw (i8, ptr addrspace(3) @g1, i32 32), align 16
+; CHECK-NEXT:    br i1 [[CMP_0]], label %[[LOOP]], label %[[SINK:.*]]
+; CHECK:       [[SINK]]:
+; CHECK-NEXT:    [[VAL_SINK:%.*]] = load <2 x i64>, ptr [[PTR_PHI_R]], align 16
+; CHECK-NEXT:    ret <2 x i64> [[VAL_SINK]]
+;
+entry:
+  %coerce = alloca %struct.type, align 16, addrspace(5)
+  call void @llvm.memcpy.p5.p4.i64(ptr addrspace(5) align 16 %coerce, ptr addrspace(4) align 16 %0, i64 4096, i1 false)
+  %ptr.0 = getelementptr inbounds i8, ptr addrspace(5) %coerce, i64 0
+  %val.0 = addrspacecast ptr addrspace(5) %ptr.0 to ptr
+  br label %loop
+
+loop:
+  %ptr.phi = phi ptr [ %val.1, %loop ], [ %val.0, %entry ]
+  %ptr.1 = load ptr, ptr addrspace(3) getelementptr inbounds nuw (i8, ptr addrspace(3) @g1, i32 32), align 16
+  %val.1 = getelementptr inbounds nuw i8, ptr %ptr.1, i64 0
+  br i1 %cmp.0, label %loop, label %sink
+
+sink:
+  %val.sink = load <2 x i64>, ptr %ptr.phi, align 16
+  ret <2 x i64> %val.sink
+}
+
+declare void @llvm.memcpy.p5.p4.i64(ptr addrspace(5) noalias writeonly captures(none), ptr addrspace(4) noalias readonly captures(none), i64, i1 immarg) #0
