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      1 //===-- AllocaHoisting.cpp - Hoist allocas to the entry block --*- C++ -*-===//
      2 //
      3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
      4 // See https://llvm.org/LICENSE.txt for license information.
      5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
      6 //
      7 //===----------------------------------------------------------------------===//
      8 //
      9 // Hoist the alloca instructions in the non-entry blocks to the entry blocks.
     10 //
     11 //===----------------------------------------------------------------------===//
     12 
     13 #include "NVPTXAllocaHoisting.h"
     14 #include "llvm/CodeGen/StackProtector.h"
     15 #include "llvm/IR/Constants.h"
     16 #include "llvm/IR/Function.h"
     17 #include "llvm/IR/Instructions.h"
     18 using namespace llvm;
     19 
     20 namespace {
     21 // Hoisting the alloca instructions in the non-entry blocks to the entry
     22 // block.
     23 class NVPTXAllocaHoisting : public FunctionPass {
     24 public:
     25   static char ID; // Pass ID
     26   NVPTXAllocaHoisting() : FunctionPass(ID) {}
     27 
     28   void getAnalysisUsage(AnalysisUsage &AU) const override {
     29     AU.addPreserved<StackProtector>();
     30   }
     31 
     32   StringRef getPassName() const override {
     33     return "NVPTX specific alloca hoisting";
     34   }
     35 
     36   bool runOnFunction(Function &function) override;
     37 };
     38 } // namespace
     39 
     40 bool NVPTXAllocaHoisting::runOnFunction(Function &function) {
     41   bool functionModified = false;
     42   Function::iterator I = function.begin();
     43   Instruction *firstTerminatorInst = (I++)->getTerminator();
     44 
     45   for (Function::iterator E = function.end(); I != E; ++I) {
     46     for (BasicBlock::iterator BI = I->begin(), BE = I->end(); BI != BE;) {
     47       AllocaInst *allocaInst = dyn_cast<AllocaInst>(BI++);
     48       if (allocaInst && isa<ConstantInt>(allocaInst->getArraySize())) {
     49         allocaInst->moveBefore(firstTerminatorInst);
     50         functionModified = true;
     51       }
     52     }
     53   }
     54 
     55   return functionModified;
     56 }
     57 
     58 char NVPTXAllocaHoisting::ID = 0;
     59 
     60 namespace llvm {
     61 void initializeNVPTXAllocaHoistingPass(PassRegistry &);
     62 }
     63 
     64 INITIALIZE_PASS(
     65     NVPTXAllocaHoisting, "alloca-hoisting",
     66     "Hoisting alloca instructions in non-entry blocks to the entry block",
     67     false, false)
     68 
     69 FunctionPass *llvm::createAllocaHoisting() { return new NVPTXAllocaHoisting; }
     70