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
24using namespace llvm;
25
26namespace {
27 struct HexagonOptimizeSZextends : public FunctionPass {
28 public:
29 static char ID;
30 HexagonOptimizeSZextends() : FunctionPass(ID) {}
31 bool runOnFunction(Function &F) override;
32
33 StringRef getPassName() const override { return "Remove sign extends"; }
34
35 void getAnalysisUsage(AnalysisUsage &AU) const override {
36 AU.addPreserved<StackProtector>();
37 FunctionPass::getAnalysisUsage(AU);
38 }
39
40 bool intrinsicAlreadySextended(Intrinsic::ID IntID);
41 };
42}
43
44char HexagonOptimizeSZextends::ID = 0;
45
46INITIALIZE_PASS(HexagonOptimizeSZextends, "reargs",
47 "Remove Sign and Zero Extends for Args", false, false)
48
49bool HexagonOptimizeSZextends::intrinsicAlreadySextended(Intrinsic::ID IntID) {
50 switch(IntID) {
51 case llvm::Intrinsic::hexagon_A2_addh_l16_sat_ll:
52 return true;
53 default:
54 break;
55 }
56 return false;
57}
58
59bool HexagonOptimizeSZextends::runOnFunction(Function &F) {
60 if (skipFunction(F))
61 return false;
62
63 unsigned Idx = 0;
64 // Try to optimize sign extends in formal parameters. It's relying on
65 // callee already sign extending the values. I'm not sure if our ABI
66 // requires callee to sign extend though.
67 for (auto &Arg : F.args()) {
68 if (F.getAttributes().hasParamAttr(ArgNo: Idx, Kind: Attribute::SExt)) {
69 if (!isa<PointerType>(Val: Arg.getType())) {
70 for (Use &U : llvm::make_early_inc_range(Range: Arg.uses())) {
71 if (isa<SExtInst>(Val: U)) {
72 Instruction* Use = cast<Instruction>(Val&: U);
73 SExtInst* SI = new SExtInst(&Arg, Use->getType());
74 assert (EVT::getEVT(SI->getType()) ==
75 (EVT::getEVT(Use->getType())));
76 Use->replaceAllUsesWith(V: SI);
77 BasicBlock::iterator First = F.getEntryBlock().begin();
78 SI->insertBefore(InsertPos: First);
79 Use->eraseFromParent();
80 }
81 }
82 }
83 }
84 ++Idx;
85 }
86
87 // Try to remove redundant sext operations on Hexagon. The hardware
88 // already sign extends many 16 bit intrinsic operations to 32 bits.
89 // For example:
90 // %34 = tail call i32 @llvm.hexagon.A2.addh.l16.sat.ll(i32 %x, i32 %y)
91 // %sext233 = shl i32 %34, 16
92 // %conv52 = ashr exact i32 %sext233, 16
93 for (auto &B : F) {
94 for (auto &I : B) {
95 // Look for arithmetic shift right by 16.
96 BinaryOperator *Ashr = dyn_cast<BinaryOperator>(Val: &I);
97 if (!(Ashr && Ashr->getOpcode() == Instruction::AShr))
98 continue;
99 Value *AshrOp1 = Ashr->getOperand(i_nocapture: 1);
100 ConstantInt *C = dyn_cast<ConstantInt>(Val: AshrOp1);
101 // Right shifted by 16.
102 if (!(C && C->getSExtValue() == 16))
103 continue;
104
105 // The first operand of Ashr comes from logical shift left.
106 Instruction *Shl = dyn_cast<Instruction>(Val: Ashr->getOperand(i_nocapture: 0));
107 if (!(Shl && Shl->getOpcode() == Instruction::Shl))
108 continue;
109 Value *Intr = Shl->getOperand(i: 0);
110 Value *ShlOp1 = Shl->getOperand(i: 1);
111 C = dyn_cast<ConstantInt>(Val: ShlOp1);
112 // Left shifted by 16.
113 if (!(C && C->getSExtValue() == 16))
114 continue;
115
116 // The first operand of Shl comes from an intrinsic.
117 if (IntrinsicInst *I = dyn_cast<IntrinsicInst>(Val: Intr)) {
118 if (!intrinsicAlreadySextended(IntID: I->getIntrinsicID()))
119 continue;
120 // All is well. Replace all uses of AShr with I.
121 for (auto UI = Ashr->user_begin(), UE = Ashr->user_end();
122 UI != UE; ++UI) {
123 const Use &TheUse = UI.getUse();
124 if (Instruction *J = dyn_cast<Instruction>(Val: TheUse.getUser())) {
125 J->replaceUsesOfWith(From: Ashr, To: I);
126 }
127 }
128 }
129 }
130 }
131
132 return true;
133}
134
135
136FunctionPass *llvm::createHexagonOptimizeSZextends() {
137 return new HexagonOptimizeSZextends();
138}
139