NVPTXLowerAlloca.cpp revision 360784 
1//===-- NVPTXLowerAlloca.cpp - Make alloca to use local memory =====--===//
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// For all alloca instructions, and add a pair of cast to local address for
10// each of them. For example,
11//
12//   %A = alloca i32
13//   store i32 0, i32* %A ; emits st.u32
14//
15// will be transformed to
16//
17//   %A = alloca i32
18//   %Local = addrspacecast i32* %A to i32 addrspace(5)*
19//   %Generic = addrspacecast i32 addrspace(5)* %A to i32*
20//   store i32 0, i32 addrspace(5)* %Generic ; emits st.local.u32
21//
22// And we will rely on NVPTXInferAddressSpaces to combine the last two
23// instructions.
24//
25//===----------------------------------------------------------------------===//
26
27#include "NVPTX.h"
28#include "NVPTXUtilities.h"
29#include "MCTargetDesc/NVPTXBaseInfo.h"
30#include "llvm/IR/Function.h"
31#include "llvm/IR/Instructions.h"
32#include "llvm/IR/IntrinsicInst.h"
33#include "llvm/IR/Module.h"
34#include "llvm/IR/Type.h"
35#include "llvm/Pass.h"
36
37using namespace llvm;
38
39namespace llvm {
40void initializeNVPTXLowerAllocaPass(PassRegistry &);
41}
42
43namespace {
44class NVPTXLowerAlloca : public FunctionPass {
45  bool runOnFunction(Function &F) override;
46
47public:
48  static char ID; // Pass identification, replacement for typeid
49  NVPTXLowerAlloca() : FunctionPass(ID) {}
50  StringRef getPassName() const override {
51    return "convert address space of alloca'ed memory to local";
52  }
53};
54} // namespace
55
56char NVPTXLowerAlloca::ID = 1;
57
58INITIALIZE_PASS(NVPTXLowerAlloca, "nvptx-lower-alloca",
59                "Lower Alloca", false, false)
60
61// =============================================================================
62// Main function for this pass.
63// =============================================================================
64bool NVPTXLowerAlloca::runOnFunction(Function &F) {
65  if (skipFunction(F))
66    return false;
67
68  bool Changed = false;
69  for (auto &BB : F)
70    for (auto &I : BB) {
71      if (auto allocaInst = dyn_cast<AllocaInst>(&I)) {
72        Changed = true;
73        auto ETy = cast<PointerType>(allocaInst->getType())->getElementType();
74        auto LocalAddrTy = PointerType::get(ETy, ADDRESS_SPACE_LOCAL);
75        auto NewASCToLocal = new AddrSpaceCastInst(allocaInst, LocalAddrTy, "");
76        auto GenericAddrTy = PointerType::get(ETy, ADDRESS_SPACE_GENERIC);
77        auto NewASCToGeneric =
78            new AddrSpaceCastInst(NewASCToLocal, GenericAddrTy, "");
79        NewASCToLocal->insertAfter(allocaInst);
80        NewASCToGeneric->insertAfter(NewASCToLocal);
81        for (Value::use_iterator UI = allocaInst->use_begin(),
82                                 UE = allocaInst->use_end();
83             UI != UE;) {
84          // Check Load, Store, GEP, and BitCast Uses on alloca and make them
85          // use the converted generic address, in order to expose non-generic
86          // addrspacecast to NVPTXInferAddressSpaces. For other types
87          // of instructions this is unnecessary and may introduce redundant
88          // address cast.
89          const auto &AllocaUse = *UI++;
90          auto LI = dyn_cast<LoadInst>(AllocaUse.getUser());
91          if (LI && LI->getPointerOperand() == allocaInst &&
92              !LI->isVolatile()) {
93            LI->setOperand(LI->getPointerOperandIndex(), NewASCToGeneric);
94            continue;
95          }
96          auto SI = dyn_cast<StoreInst>(AllocaUse.getUser());
97          if (SI && SI->getPointerOperand() == allocaInst &&
98              !SI->isVolatile()) {
99            SI->setOperand(SI->getPointerOperandIndex(), NewASCToGeneric);
100            continue;
101          }
102          auto GI = dyn_cast<GetElementPtrInst>(AllocaUse.getUser());
103          if (GI && GI->getPointerOperand() == allocaInst) {
104            GI->setOperand(GI->getPointerOperandIndex(), NewASCToGeneric);
105            continue;
106          }
107          auto BI = dyn_cast<BitCastInst>(AllocaUse.getUser());
108          if (BI && BI->getOperand(0) == allocaInst) {
109            BI->setOperand(0, NewASCToGeneric);
110            continue;
111          }
112        }
113      }
114    }
115  return Changed;
116}
117
118FunctionPass *llvm::createNVPTXLowerAllocaPass() {
119  return new NVPTXLowerAlloca();
120}
121