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> {
getPassName() const26 StringRef getPassName() const override {
27 return "WebAssembly Optimize Returned";
28 }
29
getAnalysisUsage(AnalysisUsage & AU) const30 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;
OptimizeReturned()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
createWebAssemblyOptimizeReturned()54 FunctionPass *llvm::createWebAssemblyOptimizeReturned() {
55 return new OptimizeReturned();
56 }
57
visitCallBase(CallBase & CB)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
runOnFunction(Function & F)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