1//===-- BPFASpaceCastSimplifyPass.cpp - BPF addrspacecast simplications --===//
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#include "BPF.h"
10#include <optional>
11
12#define DEBUG_TYPE "bpf-aspace-simplify"
13
14using namespace llvm;
15
16namespace {
17
18struct CastGEPCast {
19 AddrSpaceCastInst *OuterCast;
20
21 // Match chain of instructions:
22 // %inner = addrspacecast N->M
23 // %gep = getelementptr %inner, ...
24 // %outer = addrspacecast M->N %gep
25 // Where I is %outer.
26 static std::optional<CastGEPCast> match(Value *I) {
27 auto *OuterCast = dyn_cast<AddrSpaceCastInst>(Val: I);
28 if (!OuterCast)
29 return std::nullopt;
30 auto *GEP = dyn_cast<GetElementPtrInst>(Val: OuterCast->getPointerOperand());
31 if (!GEP)
32 return std::nullopt;
33 auto *InnerCast = dyn_cast<AddrSpaceCastInst>(Val: GEP->getPointerOperand());
34 if (!InnerCast)
35 return std::nullopt;
36 if (InnerCast->getSrcAddressSpace() != OuterCast->getDestAddressSpace())
37 return std::nullopt;
38 if (InnerCast->getDestAddressSpace() != OuterCast->getSrcAddressSpace())
39 return std::nullopt;
40 return CastGEPCast{.OuterCast: OuterCast};
41 }
42
43 static PointerType *changeAddressSpace(PointerType *Ty, unsigned AS) {
44 return Ty->get(C&: Ty->getContext(), AddressSpace: AS);
45 }
46
47 // Assuming match(this->OuterCast) is true, convert:
48 // (addrspacecast M->N (getelementptr (addrspacecast N->M ptr) ...))
49 // To:
50 // (getelementptr ptr ...)
51 GetElementPtrInst *rewrite() {
52 auto *GEP = cast<GetElementPtrInst>(Val: OuterCast->getPointerOperand());
53 auto *InnerCast = cast<AddrSpaceCastInst>(Val: GEP->getPointerOperand());
54 unsigned AS = OuterCast->getDestAddressSpace();
55 auto *NewGEP = cast<GetElementPtrInst>(Val: GEP->clone());
56 NewGEP->setName(GEP->getName());
57 NewGEP->insertAfter(InsertPos: OuterCast->getIterator());
58 NewGEP->setOperand(i_nocapture: 0, Val_nocapture: InnerCast->getPointerOperand());
59 auto *GEPTy = cast<PointerType>(Val: GEP->getType());
60 NewGEP->mutateType(Ty: changeAddressSpace(Ty: GEPTy, AS));
61 OuterCast->replaceAllUsesWith(V: NewGEP);
62 OuterCast->eraseFromParent();
63 if (GEP->use_empty())
64 GEP->eraseFromParent();
65 if (InnerCast->use_empty())
66 InnerCast->eraseFromParent();
67 return NewGEP;
68 }
69};
70
71} // anonymous namespace
72
73PreservedAnalyses BPFASpaceCastSimplifyPass::run(Function &F,
74 FunctionAnalysisManager &AM) {
75 SmallVector<CastGEPCast, 16> WorkList;
76 bool Changed = false;
77 for (BasicBlock &BB : F) {
78 for (Instruction &I : BB)
79 if (auto It = CastGEPCast::match(I: &I))
80 WorkList.push_back(Elt: It.value());
81 Changed |= !WorkList.empty();
82
83 while (!WorkList.empty()) {
84 CastGEPCast InsnChain = WorkList.pop_back_val();
85 GetElementPtrInst *NewGEP = InsnChain.rewrite();
86 for (User *U : NewGEP->users())
87 if (auto It = CastGEPCast::match(I: U))
88 WorkList.push_back(Elt: It.value());
89 }
90 }
91 return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
92}
93