1 //===- HexagonOptimizeSZextends.cpp - Remove unnecessary argument extends -===//
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 // Pass that removes sign extends for function parameters. These parameters
10 // are already sign extended by the caller per Hexagon's ABI
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "Hexagon.h"
15 #include "llvm/CodeGen/StackProtector.h"
16 #include "llvm/CodeGen/ValueTypes.h"
17 #include "llvm/IR/Function.h"
18 #include "llvm/IR/Instructions.h"
19 #include "llvm/IR/IntrinsicInst.h"
20 #include "llvm/IR/IntrinsicsHexagon.h"
21 #include "llvm/Pass.h"
22 #include "llvm/Transforms/Scalar.h"
23
24 using namespace llvm;
25
26 namespace llvm {
27 FunctionPass *createHexagonOptimizeSZextends();
28 void initializeHexagonOptimizeSZextendsPass(PassRegistry&);
29 }
30
31 namespace {
32 struct HexagonOptimizeSZextends : public FunctionPass {
33 public:
34 static char ID;
HexagonOptimizeSZextends__anonc94afc8f0111::HexagonOptimizeSZextends35 HexagonOptimizeSZextends() : FunctionPass(ID) {
36 initializeHexagonOptimizeSZextendsPass(*PassRegistry::getPassRegistry());
37 }
38 bool runOnFunction(Function &F) override;
39
getPassName__anonc94afc8f0111::HexagonOptimizeSZextends40 StringRef getPassName() const override { return "Remove sign extends"; }
41
getAnalysisUsage__anonc94afc8f0111::HexagonOptimizeSZextends42 void getAnalysisUsage(AnalysisUsage &AU) const override {
43 AU.addPreserved<StackProtector>();
44 FunctionPass::getAnalysisUsage(AU);
45 }
46
47 bool intrinsicAlreadySextended(Intrinsic::ID IntID);
48 };
49 }
50
51 char HexagonOptimizeSZextends::ID = 0;
52
53 INITIALIZE_PASS(HexagonOptimizeSZextends, "reargs",
54 "Remove Sign and Zero Extends for Args", false, false)
55
intrinsicAlreadySextended(Intrinsic::ID IntID)56 bool HexagonOptimizeSZextends::intrinsicAlreadySextended(Intrinsic::ID IntID) {
57 switch(IntID) {
58 case llvm::Intrinsic::hexagon_A2_addh_l16_sat_ll:
59 return true;
60 default:
61 break;
62 }
63 return false;
64 }
65
runOnFunction(Function & F)66 bool HexagonOptimizeSZextends::runOnFunction(Function &F) {
67 if (skipFunction(F))
68 return false;
69
70 unsigned Idx = 0;
71 // Try to optimize sign extends in formal parameters. It's relying on
72 // callee already sign extending the values. I'm not sure if our ABI
73 // requires callee to sign extend though.
74 for (auto &Arg : F.args()) {
75 if (F.getAttributes().hasParamAttr(Idx, Attribute::SExt)) {
76 if (!isa<PointerType>(Arg.getType())) {
77 for (Use &U : llvm::make_early_inc_range(Arg.uses())) {
78 if (isa<SExtInst>(U)) {
79 Instruction* Use = cast<Instruction>(U);
80 SExtInst* SI = new SExtInst(&Arg, Use->getType());
81 assert (EVT::getEVT(SI->getType()) ==
82 (EVT::getEVT(Use->getType())));
83 Use->replaceAllUsesWith(SI);
84 Instruction* First = &F.getEntryBlock().front();
85 SI->insertBefore(First);
86 Use->eraseFromParent();
87 }
88 }
89 }
90 }
91 ++Idx;
92 }
93
94 // Try to remove redundant sext operations on Hexagon. The hardware
95 // already sign extends many 16 bit intrinsic operations to 32 bits.
96 // For example:
97 // %34 = tail call i32 @llvm.hexagon.A2.addh.l16.sat.ll(i32 %x, i32 %y)
98 // %sext233 = shl i32 %34, 16
99 // %conv52 = ashr exact i32 %sext233, 16
100 for (auto &B : F) {
101 for (auto &I : B) {
102 // Look for arithmetic shift right by 16.
103 BinaryOperator *Ashr = dyn_cast<BinaryOperator>(&I);
104 if (!(Ashr && Ashr->getOpcode() == Instruction::AShr))
105 continue;
106 Value *AshrOp1 = Ashr->getOperand(1);
107 ConstantInt *C = dyn_cast<ConstantInt>(AshrOp1);
108 // Right shifted by 16.
109 if (!(C && C->getSExtValue() == 16))
110 continue;
111
112 // The first operand of Ashr comes from logical shift left.
113 Instruction *Shl = dyn_cast<Instruction>(Ashr->getOperand(0));
114 if (!(Shl && Shl->getOpcode() == Instruction::Shl))
115 continue;
116 Value *Intr = Shl->getOperand(0);
117 Value *ShlOp1 = Shl->getOperand(1);
118 C = dyn_cast<ConstantInt>(ShlOp1);
119 // Left shifted by 16.
120 if (!(C && C->getSExtValue() == 16))
121 continue;
122
123 // The first operand of Shl comes from an intrinsic.
124 if (IntrinsicInst *I = dyn_cast<IntrinsicInst>(Intr)) {
125 if (!intrinsicAlreadySextended(I->getIntrinsicID()))
126 continue;
127 // All is well. Replace all uses of AShr with I.
128 for (auto UI = Ashr->user_begin(), UE = Ashr->user_end();
129 UI != UE; ++UI) {
130 const Use &TheUse = UI.getUse();
131 if (Instruction *J = dyn_cast<Instruction>(TheUse.getUser())) {
132 J->replaceUsesOfWith(Ashr, I);
133 }
134 }
135 }
136 }
137 }
138
139 return true;
140 }
141
142
createHexagonOptimizeSZextends()143 FunctionPass *llvm::createHexagonOptimizeSZextends() {
144 return new HexagonOptimizeSZextends();
145 }
146