1//===-- PPCLowerMASSVEntries.cpp ------------------------------------------===//
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// This file implements lowering of MASSV (SIMD) entries for specific PowerPC
10// subtargets.
11// Following is an example of a conversion specific to Power9 subtarget:
12// __sind2_massv ---> __sind2_P9
13//
14//===----------------------------------------------------------------------===//
15
16#include "PPC.h"
17#include "PPCSubtarget.h"
18#include "PPCTargetMachine.h"
19#include "llvm/Analysis/TargetTransformInfo.h"
20#include "llvm/CodeGen/TargetPassConfig.h"
21#include "llvm/IR/Instructions.h"
22#include "llvm/IR/Module.h"
23
24#define DEBUG_TYPE "ppc-lower-massv-entries"
25
26using namespace llvm;
27
28namespace {
29
30// Length of the suffix "massv", which is specific to IBM MASSV library entries.
31const unsigned MASSVSuffixLength = 5;
32
33static StringRef MASSVFuncs[] = {
34#define TLI_DEFINE_MASSV_VECFUNCS_NAMES
35#include "llvm/Analysis/VecFuncs.def"
36};
37
38class PPCLowerMASSVEntries : public ModulePass {
39public:
40  static char ID;
41
42  PPCLowerMASSVEntries() : ModulePass(ID) {}
43
44  bool runOnModule(Module &M) override;
45
46  StringRef getPassName() const override { return "PPC Lower MASS Entries"; }
47
48  void getAnalysisUsage(AnalysisUsage &AU) const override {
49    AU.addRequired<TargetTransformInfoWrapperPass>();
50  }
51
52private:
53  static bool isMASSVFunc(StringRef Name);
54  static StringRef getCPUSuffix(const PPCSubtarget *Subtarget);
55  static std::string createMASSVFuncName(Function &Func,
56                                         const PPCSubtarget *Subtarget);
57  bool handlePowSpecialCases(CallInst *CI, Function &Func, Module &M);
58  bool lowerMASSVCall(CallInst *CI, Function &Func, Module &M,
59                      const PPCSubtarget *Subtarget);
60};
61
62} // namespace
63
64/// Checks if the specified function name represents an entry in the MASSV
65/// library.
66bool PPCLowerMASSVEntries::isMASSVFunc(StringRef Name) {
67  auto Iter = std::find(std::begin(MASSVFuncs), std::end(MASSVFuncs), Name);
68  return Iter != std::end(MASSVFuncs);
69}
70
71// FIXME:
72/// Returns a string corresponding to the specified PowerPC subtarget. e.g.:
73/// "P8" for Power8, "P9" for Power9. The string is used as a suffix while
74/// generating subtarget-specific MASSV library functions. Current support
75/// includes  Power8 and Power9 subtargets.
76StringRef PPCLowerMASSVEntries::getCPUSuffix(const PPCSubtarget *Subtarget) {
77  // Assume Power8 when Subtarget is unavailable.
78  if (!Subtarget)
79    return "P8";
80  if (Subtarget->hasP9Vector())
81    return "P9";
82  if (Subtarget->hasP8Vector())
83    return "P8";
84
85  report_fatal_error("Unsupported Subtarget: MASSV is supported only on "
86                     "Power8 and Power9 subtargets.");
87}
88
89/// Creates PowerPC subtarget-specific name corresponding to the specified
90/// generic MASSV function, and the PowerPC subtarget.
91std::string
92PPCLowerMASSVEntries::createMASSVFuncName(Function &Func,
93                                          const PPCSubtarget *Subtarget) {
94  StringRef Suffix = getCPUSuffix(Subtarget);
95  auto GenericName = Func.getName().drop_back(MASSVSuffixLength).str();
96  std::string MASSVEntryName = GenericName + Suffix.str();
97  return MASSVEntryName;
98}
99
100/// If there are proper fast-math flags, this function creates llvm.pow
101/// intrinsics when the exponent is 0.25 or 0.75.
102bool PPCLowerMASSVEntries::handlePowSpecialCases(CallInst *CI, Function &Func,
103                                                 Module &M) {
104  if (Func.getName() != "__powf4_massv" && Func.getName() != "__powd2_massv")
105    return false;
106
107  if (Constant *Exp = dyn_cast<Constant>(CI->getArgOperand(1)))
108    if (ConstantFP *CFP = dyn_cast<ConstantFP>(Exp->getSplatValue())) {
109      // If the argument is 0.75 or 0.25 it is cheaper to turn it into pow
110      // intrinsic so that it could be optimzed as sequence of sqrt's.
111      if (!CI->hasNoInfs() || !CI->hasApproxFunc())
112        return false;
113
114      if (!CFP->isExactlyValue(0.75) && !CFP->isExactlyValue(0.25))
115        return false;
116
117      if (CFP->isExactlyValue(0.25) && !CI->hasNoSignedZeros())
118        return false;
119
120      CI->setCalledFunction(
121          Intrinsic::getDeclaration(&M, Intrinsic::pow, CI->getType()));
122      return true;
123    }
124
125  return false;
126}
127
128/// Lowers generic MASSV entries to PowerPC subtarget-specific MASSV entries.
129/// e.g.: __sind2_massv --> __sind2_P9 for a Power9 subtarget.
130/// Both function prototypes and their callsites are updated during lowering.
131bool PPCLowerMASSVEntries::lowerMASSVCall(CallInst *CI, Function &Func,
132                                          Module &M,
133                                          const PPCSubtarget *Subtarget) {
134  if (CI->use_empty())
135    return false;
136
137  // Handling pow(x, 0.25), pow(x, 0.75), powf(x, 0.25), powf(x, 0.75)
138  if (handlePowSpecialCases(CI, Func, M))
139    return true;
140
141  std::string MASSVEntryName = createMASSVFuncName(Func, Subtarget);
142  FunctionCallee FCache = M.getOrInsertFunction(
143      MASSVEntryName, Func.getFunctionType(), Func.getAttributes());
144
145  CI->setCalledFunction(FCache);
146
147  return true;
148}
149
150bool PPCLowerMASSVEntries::runOnModule(Module &M) {
151  bool Changed = false;
152
153  auto *TPC = getAnalysisIfAvailable<TargetPassConfig>();
154  if (!TPC)
155    return Changed;
156
157  auto &TM = TPC->getTM<PPCTargetMachine>();
158  const PPCSubtarget *Subtarget;
159
160  for (Function &Func : M) {
161    if (!Func.isDeclaration())
162      continue;
163
164    if (!isMASSVFunc(Func.getName()))
165      continue;
166
167    // Call to lowerMASSVCall() invalidates the iterator over users upon
168    // replacing the users. Precomputing the current list of users allows us to
169    // replace all the call sites.
170    SmallVector<User *, 4> MASSVUsers;
171    for (auto *User: Func.users())
172      MASSVUsers.push_back(User);
173
174    for (auto *User : MASSVUsers) {
175      auto *CI = dyn_cast<CallInst>(User);
176      if (!CI)
177        continue;
178
179      Subtarget = &TM.getSubtarget<PPCSubtarget>(*CI->getParent()->getParent());
180      Changed |= lowerMASSVCall(CI, Func, M, Subtarget);
181    }
182  }
183
184  return Changed;
185}
186
187char PPCLowerMASSVEntries::ID = 0;
188
189char &llvm::PPCLowerMASSVEntriesID = PPCLowerMASSVEntries::ID;
190
191INITIALIZE_PASS(PPCLowerMASSVEntries, DEBUG_TYPE, "Lower MASSV entries", false,
192                false)
193
194ModulePass *llvm::createPPCLowerMASSVEntriesPass() {
195  return new PPCLowerMASSVEntries();
196}
197