[llvm] [PredicateInfo] Support `PredicateInfo` by adding `PHI` nodes that pick up info from created branch predicates (PR #151132)

[Yingwei Zheng via llvm-commits]

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@@ -460,6 +471,114 @@ void PredicateInfoBuilder::processSwitch(
   }
 }
 
+void PredicateInfoBuilder::identifyPHICandidates(
+    SmallVectorImpl<Value *> &OpsToRename) {
+  for (Value *Op : OpsToRename) {
+    const auto &ValueInfo = getValueInfo(Op);
+    SmallPtrSet<BasicBlock *, 4> DefiningBlocks;
+    for (const auto *PInfo : ValueInfo.Infos) {
+      if (auto *PBranch = dyn_cast<PredicateBranch>(PInfo)) {
+        DefiningBlocks.insert(PBranch->From);
+      } else if (auto *PSwitch = dyn_cast<PredicateSwitch>(PInfo)) {
+        DefiningBlocks.insert(PSwitch->From);
+      }
+    }
+
+    if (DefiningBlocks.size() > 1) {
+      SmallPtrSet<BasicBlock *, 8> PHIBlocks;
+      needsPHIInsertion(Op, DefiningBlocks, PHIBlocks);
+      for (BasicBlock *PHIBlock : PHIBlocks) {
+        PHICandidates[PHIBlock].push_back(Op);
+      }
+    }
+  }
+}
+
+void PredicateInfoBuilder::needsPHIInsertion(
+    Value *Op, const SmallPtrSetImpl<BasicBlock *> &DefiningBlocks,
+    SmallPtrSetImpl<BasicBlock *> &PHIBlocks) {
+  IDFCalculator<false> IDF(DT);
+  IDF.setDefiningBlocks(DefiningBlocks);
+
+  SmallPtrSet<BasicBlock *, 8> LiveInBlocks;
+  for (auto CurUser = Op->users().begin(); CurUser != Op->users().end();
+       ++CurUser) {
+    if (auto *I = dyn_cast<Instruction>(*CurUser)) {
+      LiveInBlocks.insert(I->getParent());
+    }
+  }
+  IDF.setLiveInBlocks(LiveInBlocks);
+
+  SmallVector<BasicBlock *, 4> IDFBlocks;
+  IDF.calculate(IDFBlocks);
+
+  for (const auto &IDFBlock : IDFBlocks) {
+    PHIBlocks.insert(std::move(IDFBlock));
+  }
+}
+
+PHINode *PredicateInfoBuilder::insertPredicatePHIs(
+    Value *Op, BasicBlock *PHIBlock, SmallVectorImpl<Value *> &OpsToRename) {
+  IRBuilder<> Builder(&PHIBlock->front());
+
+  PHINode *PHI = Builder.CreatePHI(Op->getType(), pred_size(PHIBlock),
+                                   Op->getName() + ".predicate.phi");
+  const auto &ValueInfo = getValueInfo(Op);
+
+  for (BasicBlock *Pred : predecessors(PHIBlock)) {
+    Value *IncomingValue = nullptr;
+    for (const auto *PInfo : ValueInfo.Infos) {
+      if (auto *PBranch = dyn_cast<PredicateBranch>(PInfo)) {
+        if (PBranch->From == Pred && PBranch->To == PHIBlock) {
+          IncomingValue = PBranch->OriginalOp;
+        }
+      } else if (auto *PSwitch = dyn_cast<PredicateSwitch>(PInfo)) {
+        if (PSwitch->From == Pred && PSwitch->To == PHIBlock) {
+          IncomingValue = PSwitch->OriginalOp;
+        }
+      }
+    }
+    if (IncomingValue) {
+      PHI->addIncoming(IncomingValue, Pred);
+    } else {
+      PHI->eraseFromParent();
+      return nullptr;
+    }
+  }
+
+  return PHI;
+}
+
+void PredicateInfoBuilder::processPredicatePHIs(
+    SmallVectorImpl<Value *> &OpsToRename) {
+  SmallVector<PHINode *, 4> InsertedPHINodes;
+
+  for (const auto &PHICandidate : PHICandidates) {
+    BasicBlock *PHIBlock = PHICandidate.first;
+    for (Value *Op : PHICandidate.second) {
+      auto *PHI = insertPredicatePHIs(Op, PHIBlock, OpsToRename);
+      InsertedPHINodes.push_back(PHI);
+    }
+  }
+
+  size_t Idx = 0, NumNodes = InsertedPHINodes.size();
+  for (const auto &PHICandidate : PHICandidates) {
+    BasicBlock *PHIBlock = PHICandidate.first;
+    for (Value *Op : PHICandidate.second) {
+      while (Idx < NumNodes && InsertedPHINodes[Idx] == nullptr) {
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dtcxzyw wrote:

I don't understand this part. Can you add some comments?

https://github.com/llvm/llvm-project/pull/151132