1 //===- InjectTLIMAppings.cpp - TLI to VFABI attribute injection  ----------===//
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 // Populates the VFABI attribute with the scalar-to-vector mappings
10 // from the TargetLibraryInfo.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/Transforms/Utils/InjectTLIMappings.h"
15 #include "llvm/ADT/Statistic.h"
16 #include "llvm/Analysis/DemandedBits.h"
17 #include "llvm/Analysis/GlobalsModRef.h"
18 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
19 #include "llvm/Analysis/TargetLibraryInfo.h"
20 #include "llvm/Analysis/VectorUtils.h"
21 #include "llvm/IR/InstIterator.h"
22 #include "llvm/IR/VFABIDemangler.h"
23 #include "llvm/Transforms/Utils/ModuleUtils.h"
24 
25 using namespace llvm;
26 
27 #define DEBUG_TYPE "inject-tli-mappings"
28 
29 STATISTIC(NumCallInjected,
30           "Number of calls in which the mappings have been injected.");
31 
32 STATISTIC(NumVFDeclAdded,
33           "Number of function declarations that have been added.");
34 STATISTIC(NumCompUsedAdded,
35           "Number of `@llvm.compiler.used` operands that have been added.");
36 
37 /// A helper function that adds the vector variant declaration for vectorizing
38 /// the CallInst \p CI with a vectorization factor of \p VF lanes. For each
39 /// mapping, TLI provides a VABI prefix, which contains all information required
40 /// to create vector function declaration.
41 static void addVariantDeclaration(CallInst &CI, const ElementCount &VF,
42                                   const VecDesc *VD) {
43   Module *M = CI.getModule();
44   FunctionType *ScalarFTy = CI.getFunctionType();
45 
46   assert(!ScalarFTy->isVarArg() && "VarArg functions are not supported.");
47 
48   const std::optional<VFInfo> Info = VFABI::tryDemangleForVFABI(
49       VD->getVectorFunctionABIVariantString(), ScalarFTy);
50 
51   assert(Info && "Failed to demangle vector variant");
52   assert(Info->Shape.VF == VF && "Mangled name does not match VF");
53 
54   const StringRef VFName = VD->getVectorFnName();
55   FunctionType *VectorFTy = VFABI::createFunctionType(*Info, ScalarFTy);
56   Function *VecFunc =
57       Function::Create(VectorFTy, Function::ExternalLinkage, VFName, M);
58   VecFunc->copyAttributesFrom(CI.getCalledFunction());
59   ++NumVFDeclAdded;
60   LLVM_DEBUG(dbgs() << DEBUG_TYPE << ": Added to the module: `" << VFName
61                     << "` of type " << *VectorFTy << "\n");
62 
63   // Make function declaration (without a body) "sticky" in the IR by
64   // listing it in the @llvm.compiler.used intrinsic.
65   assert(!VecFunc->size() && "VFABI attribute requires `@llvm.compiler.used` "
66                              "only on declarations.");
67   appendToCompilerUsed(*M, {VecFunc});
68   LLVM_DEBUG(dbgs() << DEBUG_TYPE << ": Adding `" << VFName
69                     << "` to `@llvm.compiler.used`.\n");
70   ++NumCompUsedAdded;
71 }
72 
73 static void addMappingsFromTLI(const TargetLibraryInfo &TLI, CallInst &CI) {
74   // This is needed to make sure we don't query the TLI for calls to
75   // bitcast of function pointers, like `%call = call i32 (i32*, ...)
76   // bitcast (i32 (...)* @goo to i32 (i32*, ...)*)(i32* nonnull %i)`,
77   // as such calls make the `isFunctionVectorizable` raise an
78   // exception.
79   if (CI.isNoBuiltin() || !CI.getCalledFunction())
80     return;
81 
82   StringRef ScalarName = CI.getCalledFunction()->getName();
83 
84   // Nothing to be done if the TLI thinks the function is not
85   // vectorizable.
86   if (!TLI.isFunctionVectorizable(ScalarName))
87     return;
88   SmallVector<std::string, 8> Mappings;
89   VFABI::getVectorVariantNames(CI, Mappings);
90   Module *M = CI.getModule();
91   const SetVector<StringRef> OriginalSetOfMappings(Mappings.begin(),
92                                                    Mappings.end());
93 
94   auto AddVariantDecl = [&](const ElementCount &VF, bool Predicate) {
95     const VecDesc *VD = TLI.getVectorMappingInfo(ScalarName, VF, Predicate);
96     if (VD && !VD->getVectorFnName().empty()) {
97       std::string MangledName = VD->getVectorFunctionABIVariantString();
98       if (!OriginalSetOfMappings.count(MangledName)) {
99         Mappings.push_back(MangledName);
100         ++NumCallInjected;
101       }
102       Function *VariantF = M->getFunction(VD->getVectorFnName());
103       if (!VariantF)
104         addVariantDeclaration(CI, VF, VD);
105     }
106   };
107 
108   //  All VFs in the TLI are powers of 2.
109   ElementCount WidestFixedVF, WidestScalableVF;
110   TLI.getWidestVF(ScalarName, WidestFixedVF, WidestScalableVF);
111 
112   for (bool Predicated : {false, true}) {
113     for (ElementCount VF = ElementCount::getFixed(2);
114          ElementCount::isKnownLE(VF, WidestFixedVF); VF *= 2)
115       AddVariantDecl(VF, Predicated);
116 
117     for (ElementCount VF = ElementCount::getScalable(2);
118          ElementCount::isKnownLE(VF, WidestScalableVF); VF *= 2)
119       AddVariantDecl(VF, Predicated);
120   }
121 
122   VFABI::setVectorVariantNames(&CI, Mappings);
123 }
124 
125 static bool runImpl(const TargetLibraryInfo &TLI, Function &F) {
126   for (auto &I : instructions(F))
127     if (auto CI = dyn_cast<CallInst>(&I))
128       addMappingsFromTLI(TLI, *CI);
129   // Even if the pass adds IR attributes, the analyses are preserved.
130   return false;
131 }
132 
133 ////////////////////////////////////////////////////////////////////////////////
134 // New pass manager implementation.
135 ////////////////////////////////////////////////////////////////////////////////
136 PreservedAnalyses InjectTLIMappings::run(Function &F,
137                                          FunctionAnalysisManager &AM) {
138   const TargetLibraryInfo &TLI = AM.getResult<TargetLibraryAnalysis>(F);
139   runImpl(TLI, F);
140   // Even if the pass adds IR attributes, the analyses are preserved.
141   return PreservedAnalyses::all();
142 }
143