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