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/ADT/STLExtras.h"
20 #include "llvm/Analysis/TargetTransformInfo.h"
21 #include "llvm/CodeGen/TargetPassConfig.h"
22 #include "llvm/IR/Instructions.h"
23 #include "llvm/IR/Module.h"
24
25 #define DEBUG_TYPE "ppc-lower-massv-entries"
26
27 using namespace llvm;
28
29 namespace {
30
31 // Length of the suffix "massv", which is specific to IBM MASSV library entries.
32 const unsigned MASSVSuffixLength = 5;
33
34 static StringRef MASSVFuncs[] = {
35 #define TLI_DEFINE_MASSV_VECFUNCS_NAMES
36 #include "llvm/Analysis/VecFuncs.def"
37 };
38
39 class PPCLowerMASSVEntries : public ModulePass {
40 public:
41 static char ID;
42
PPCLowerMASSVEntries()43 PPCLowerMASSVEntries() : ModulePass(ID) {}
44
45 bool runOnModule(Module &M) override;
46
getPassName() const47 StringRef getPassName() const override { return "PPC Lower MASS Entries"; }
48
getAnalysisUsage(AnalysisUsage & AU) const49 void getAnalysisUsage(AnalysisUsage &AU) const override {
50 AU.addRequired<TargetTransformInfoWrapperPass>();
51 }
52
53 private:
54 static bool isMASSVFunc(StringRef Name);
55 static StringRef getCPUSuffix(const PPCSubtarget *Subtarget);
56 static std::string createMASSVFuncName(Function &Func,
57 const PPCSubtarget *Subtarget);
58 bool handlePowSpecialCases(CallInst *CI, Function &Func, Module &M);
59 bool lowerMASSVCall(CallInst *CI, Function &Func, Module &M,
60 const PPCSubtarget *Subtarget);
61 };
62
63 } // namespace
64
65 /// Checks if the specified function name represents an entry in the MASSV
66 /// library.
isMASSVFunc(StringRef Name)67 bool PPCLowerMASSVEntries::isMASSVFunc(StringRef Name) {
68 return llvm::is_contained(MASSVFuncs, Name);
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.
getCPUSuffix(const PPCSubtarget * Subtarget)76 StringRef 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.
91 std::string
createMASSVFuncName(Function & Func,const PPCSubtarget * Subtarget)92 PPCLowerMASSVEntries::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.
handlePowSpecialCases(CallInst * CI,Function & Func,Module & M)102 bool 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_or_null<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.
lowerMASSVCall(CallInst * CI,Function & Func,Module & M,const PPCSubtarget * Subtarget)131 bool 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
runOnModule(Module & M)150 bool 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
187 char PPCLowerMASSVEntries::ID = 0;
188
189 char &llvm::PPCLowerMASSVEntriesID = PPCLowerMASSVEntries::ID;
190
191 INITIALIZE_PASS(PPCLowerMASSVEntries, DEBUG_TYPE, "Lower MASSV entries", false,
192 false)
193
createPPCLowerMASSVEntriesPass()194 ModulePass *llvm::createPPCLowerMASSVEntriesPass() {
195 return new PPCLowerMASSVEntries();
196 }
197