1 //===-- WebAssemblyOptimizeReturned.cpp - Optimize "returned" attributes --===//
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 /// \file
10 /// Optimize calls with "returned" attributes for WebAssembly.
11 ///
12 //===----------------------------------------------------------------------===//
13 
14 #include "WebAssembly.h"
15 #include "llvm/IR/Dominators.h"
16 #include "llvm/IR/InstVisitor.h"
17 #include "llvm/Support/Debug.h"
18 #include "llvm/Support/raw_ostream.h"
19 using namespace llvm;
20 
21 #define DEBUG_TYPE "wasm-optimize-returned"
22 
23 namespace {
24 class OptimizeReturned final : public FunctionPass,
25                                public InstVisitor<OptimizeReturned> {
26   StringRef getPassName() const override {
27     return "WebAssembly Optimize Returned";
28   }
29 
30   void getAnalysisUsage(AnalysisUsage &AU) const override {
31     AU.setPreservesCFG();
32     AU.addRequired<DominatorTreeWrapperPass>();
33     AU.addPreserved<DominatorTreeWrapperPass>();
34     FunctionPass::getAnalysisUsage(AU);
35   }
36 
37   bool runOnFunction(Function &F) override;
38 
39   DominatorTree *DT = nullptr;
40 
41 public:
42   static char ID;
43   OptimizeReturned() : FunctionPass(ID) {}
44 
45   void visitCallBase(CallBase &CB);
46 };
47 } // End anonymous namespace
48 
49 char OptimizeReturned::ID = 0;
50 INITIALIZE_PASS(OptimizeReturned, DEBUG_TYPE,
51                 "Optimize calls with \"returned\" attributes for WebAssembly",
52                 false, false)
53 
54 FunctionPass *llvm::createWebAssemblyOptimizeReturned() {
55   return new OptimizeReturned();
56 }
57 
58 void OptimizeReturned::visitCallBase(CallBase &CB) {
59   for (unsigned I = 0, E = CB.arg_size(); I < E; ++I)
60     if (CB.paramHasAttr(I, Attribute::Returned)) {
61       Value *Arg = CB.getArgOperand(I);
62       // Ignore constants, globals, undef, etc.
63       if (isa<Constant>(Arg))
64         continue;
65       // Like replaceDominatedUsesWith but using Instruction/Use dominance.
66       Arg->replaceUsesWithIf(&CB,
67                              [&](Use &U) { return DT->dominates(&CB, U); });
68     }
69 }
70 
71 bool OptimizeReturned::runOnFunction(Function &F) {
72   LLVM_DEBUG(dbgs() << "********** Optimize returned Attributes **********\n"
73                        "********** Function: "
74                     << F.getName() << '\n');
75 
76   DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
77   visit(F);
78   return true;
79 }
80