1 //===- NVVMReflect.cpp - NVVM Emulate conditional compilation -------------===//
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 pass replaces occurrences of __nvvm_reflect("foo") and llvm.nvvm.reflect
10 // with an integer.
11 //
12 // We choose the value we use by looking at metadata in the module itself. Note
13 // that we intentionally only have one way to choose these values, because other
14 // parts of LLVM (particularly, InstCombineCall) rely on being able to predict
15 // the values chosen by this pass.
16 //
17 // If we see an unknown string, we replace its call with 0.
18 //
19 //===----------------------------------------------------------------------===//
20
21 #include "NVPTX.h"
22 #include "llvm/ADT/SmallVector.h"
23 #include "llvm/ADT/StringMap.h"
24 #include "llvm/IR/Constants.h"
25 #include "llvm/IR/DerivedTypes.h"
26 #include "llvm/IR/Function.h"
27 #include "llvm/IR/InstIterator.h"
28 #include "llvm/IR/Instructions.h"
29 #include "llvm/IR/Intrinsics.h"
30 #include "llvm/IR/IntrinsicsNVPTX.h"
31 #include "llvm/IR/Module.h"
32 #include "llvm/IR/PassManager.h"
33 #include "llvm/IR/Type.h"
34 #include "llvm/Pass.h"
35 #include "llvm/Support/CommandLine.h"
36 #include "llvm/Support/Debug.h"
37 #include "llvm/Support/raw_os_ostream.h"
38 #include "llvm/Support/raw_ostream.h"
39 #include "llvm/Transforms/Scalar.h"
40 #include <sstream>
41 #include <string>
42 #define NVVM_REFLECT_FUNCTION "__nvvm_reflect"
43 #define NVVM_REFLECT_OCL_FUNCTION "__nvvm_reflect_ocl"
44
45 using namespace llvm;
46
47 #define DEBUG_TYPE "nvptx-reflect"
48
49 namespace llvm { void initializeNVVMReflectPass(PassRegistry &); }
50
51 namespace {
52 class NVVMReflect : public FunctionPass {
53 public:
54 static char ID;
55 unsigned int SmVersion;
NVVMReflect()56 NVVMReflect() : NVVMReflect(0) {}
NVVMReflect(unsigned int Sm)57 explicit NVVMReflect(unsigned int Sm) : FunctionPass(ID), SmVersion(Sm) {
58 initializeNVVMReflectPass(*PassRegistry::getPassRegistry());
59 }
60
61 bool runOnFunction(Function &) override;
62 };
63 }
64
createNVVMReflectPass(unsigned int SmVersion)65 FunctionPass *llvm::createNVVMReflectPass(unsigned int SmVersion) {
66 return new NVVMReflect(SmVersion);
67 }
68
69 static cl::opt<bool>
70 NVVMReflectEnabled("nvvm-reflect-enable", cl::init(true), cl::Hidden,
71 cl::desc("NVVM reflection, enabled by default"));
72
73 char NVVMReflect::ID = 0;
74 INITIALIZE_PASS(NVVMReflect, "nvvm-reflect",
75 "Replace occurrences of __nvvm_reflect() calls with 0/1", false,
76 false)
77
runNVVMReflect(Function & F,unsigned SmVersion)78 static bool runNVVMReflect(Function &F, unsigned SmVersion) {
79 if (!NVVMReflectEnabled)
80 return false;
81
82 if (F.getName() == NVVM_REFLECT_FUNCTION ||
83 F.getName() == NVVM_REFLECT_OCL_FUNCTION) {
84 assert(F.isDeclaration() && "_reflect function should not have a body");
85 assert(F.getReturnType()->isIntegerTy() &&
86 "_reflect's return type should be integer");
87 return false;
88 }
89
90 SmallVector<Instruction *, 4> ToRemove;
91
92 // Go through the calls in this function. Each call to __nvvm_reflect or
93 // llvm.nvvm.reflect should be a CallInst with a ConstantArray argument.
94 // First validate that. If the c-string corresponding to the ConstantArray can
95 // be found successfully, see if it can be found in VarMap. If so, replace the
96 // uses of CallInst with the value found in VarMap. If not, replace the use
97 // with value 0.
98
99 // The IR for __nvvm_reflect calls differs between CUDA versions.
100 //
101 // CUDA 6.5 and earlier uses this sequence:
102 // %ptr = tail call i8* @llvm.nvvm.ptr.constant.to.gen.p0i8.p4i8
103 // (i8 addrspace(4)* getelementptr inbounds
104 // ([8 x i8], [8 x i8] addrspace(4)* @str, i32 0, i32 0))
105 // %reflect = tail call i32 @__nvvm_reflect(i8* %ptr)
106 //
107 // The value returned by Sym->getOperand(0) is a Constant with a
108 // ConstantDataSequential operand which can be converted to string and used
109 // for lookup.
110 //
111 // CUDA 7.0 does it slightly differently:
112 // %reflect = call i32 @__nvvm_reflect(i8* addrspacecast
113 // (i8 addrspace(1)* getelementptr inbounds
114 // ([8 x i8], [8 x i8] addrspace(1)* @str, i32 0, i32 0) to i8*))
115 //
116 // In this case, we get a Constant with a GlobalVariable operand and we need
117 // to dig deeper to find its initializer with the string we'll use for lookup.
118 for (Instruction &I : instructions(F)) {
119 CallInst *Call = dyn_cast<CallInst>(&I);
120 if (!Call)
121 continue;
122 Function *Callee = Call->getCalledFunction();
123 if (!Callee || (Callee->getName() != NVVM_REFLECT_FUNCTION &&
124 Callee->getName() != NVVM_REFLECT_OCL_FUNCTION &&
125 Callee->getIntrinsicID() != Intrinsic::nvvm_reflect))
126 continue;
127
128 // FIXME: Improve error handling here and elsewhere in this pass.
129 assert(Call->getNumOperands() == 2 &&
130 "Wrong number of operands to __nvvm_reflect function");
131
132 // In cuda 6.5 and earlier, we will have an extra constant-to-generic
133 // conversion of the string.
134 const Value *Str = Call->getArgOperand(0);
135 if (const CallInst *ConvCall = dyn_cast<CallInst>(Str)) {
136 // FIXME: Add assertions about ConvCall.
137 Str = ConvCall->getArgOperand(0);
138 }
139 // Pre opaque pointers we have a constant expression wrapping the constant
140 // string.
141 Str = Str->stripPointerCasts();
142 assert(isa<Constant>(Str) &&
143 "Format of __nvvm_reflect function not recognized");
144
145 const Value *Operand = cast<Constant>(Str)->getOperand(0);
146 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Operand)) {
147 // For CUDA-7.0 style __nvvm_reflect calls, we need to find the operand's
148 // initializer.
149 assert(GV->hasInitializer() &&
150 "Format of _reflect function not recognized");
151 const Constant *Initializer = GV->getInitializer();
152 Operand = Initializer;
153 }
154
155 assert(isa<ConstantDataSequential>(Operand) &&
156 "Format of _reflect function not recognized");
157 assert(cast<ConstantDataSequential>(Operand)->isCString() &&
158 "Format of _reflect function not recognized");
159
160 StringRef ReflectArg = cast<ConstantDataSequential>(Operand)->getAsString();
161 ReflectArg = ReflectArg.substr(0, ReflectArg.size() - 1);
162 LLVM_DEBUG(dbgs() << "Arg of _reflect : " << ReflectArg << "\n");
163
164 int ReflectVal = 0; // The default value is 0
165 if (ReflectArg == "__CUDA_FTZ") {
166 // Try to pull __CUDA_FTZ from the nvvm-reflect-ftz module flag. Our
167 // choice here must be kept in sync with AutoUpgrade, which uses the same
168 // technique to detect whether ftz is enabled.
169 if (auto *Flag = mdconst::extract_or_null<ConstantInt>(
170 F.getParent()->getModuleFlag("nvvm-reflect-ftz")))
171 ReflectVal = Flag->getSExtValue();
172 } else if (ReflectArg == "__CUDA_ARCH") {
173 ReflectVal = SmVersion * 10;
174 }
175 Call->replaceAllUsesWith(ConstantInt::get(Call->getType(), ReflectVal));
176 ToRemove.push_back(Call);
177 }
178
179 for (Instruction *I : ToRemove)
180 I->eraseFromParent();
181
182 return ToRemove.size() > 0;
183 }
184
runOnFunction(Function & F)185 bool NVVMReflect::runOnFunction(Function &F) {
186 return runNVVMReflect(F, SmVersion);
187 }
188
NVVMReflectPass()189 NVVMReflectPass::NVVMReflectPass() : NVVMReflectPass(0) {}
190
run(Function & F,FunctionAnalysisManager & AM)191 PreservedAnalyses NVVMReflectPass::run(Function &F,
192 FunctionAnalysisManager &AM) {
193 return runNVVMReflect(F, SmVersion) ? PreservedAnalyses::none()
194 : PreservedAnalyses::all();
195 }
196