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 
37 using namespace llvm;
38 
39 namespace llvm {
40 void initializeNVPTXLowerAllocaPass(PassRegistry &);
41 }
42 
43 namespace {
44 class NVPTXLowerAlloca : public FunctionPass {
45   bool runOnFunction(Function &F) override;
46 
47 public:
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 
56 char NVPTXLowerAlloca::ID = 1;
57 
58 INITIALIZE_PASS(NVPTXLowerAlloca, "nvptx-lower-alloca",
59                 "Lower Alloca", false, false)
60 
61 // =============================================================================
62 // Main function for this pass.
63 // =============================================================================
64 bool 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 
118 FunctionPass *llvm::createNVPTXLowerAllocaPass() {
119   return new NVPTXLowerAlloca();
120 }
121