1 //===- NVVMReflect.cpp - NVVM Emulate conditional compilation -------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass replaces occurrences of __nvvm_reflect("foo") and llvm.nvvm.reflect
13 // We choose the value we use by looking at metadata in the module itself. Note
14 // that we intentionally only have one way to choose these values, because other
15 // parts of LLVM (particularly, InstCombineCall) rely on being able to predict
16 // the values chosen by this pass.
18 // If we see an unknown string, we replace its call with 0.
20 //===----------------------------------------------------------------------===//
23 #include "llvm/ADT/SmallVector.h"
24 #include "llvm/ADT/StringMap.h"
25 #include "llvm/IR/Constants.h"
26 #include "llvm/IR/DerivedTypes.h"
27 #include "llvm/IR/Function.h"
28 #include "llvm/IR/InstIterator.h"
29 #include "llvm/IR/Instructions.h"
30 #include "llvm/IR/Intrinsics.h"
31 #include "llvm/IR/Module.h"
32 #include "llvm/IR/Type.h"
33 #include "llvm/Pass.h"
34 #include "llvm/Support/CommandLine.h"
35 #include "llvm/Support/Debug.h"
36 #include "llvm/Support/raw_os_ostream.h"
37 #include "llvm/Support/raw_ostream.h"
38 #include "llvm/Transforms/Scalar.h"
41 #define NVVM_REFLECT_FUNCTION "__nvvm_reflect"
45 #define DEBUG_TYPE "nvptx-reflect"
47 namespace llvm { void initializeNVVMReflectPass(PassRegistry &); }
50 class NVVMReflect : public FunctionPass {
53 NVVMReflect() : FunctionPass(ID) {
54 initializeNVVMReflectPass(*PassRegistry::getPassRegistry());
57 bool runOnFunction(Function &) override;
61 FunctionPass *llvm::createNVVMReflectPass() { return new NVVMReflect(); }
64 NVVMReflectEnabled("nvvm-reflect-enable", cl::init(true), cl::Hidden,
65 cl::desc("NVVM reflection, enabled by default"));
67 char NVVMReflect::ID = 0;
68 INITIALIZE_PASS(NVVMReflect, "nvvm-reflect",
69 "Replace occurrences of __nvvm_reflect() calls with 0/1", false,
72 bool NVVMReflect::runOnFunction(Function &F) {
73 if (!NVVMReflectEnabled)
76 if (F.getName() == NVVM_REFLECT_FUNCTION) {
77 assert(F.isDeclaration() && "_reflect function should not have a body");
78 assert(F.getReturnType()->isIntegerTy() &&
79 "_reflect's return type should be integer");
83 SmallVector<Instruction *, 4> ToRemove;
85 // Go through the calls in this function. Each call to __nvvm_reflect or
86 // llvm.nvvm.reflect should be a CallInst with a ConstantArray argument.
87 // First validate that. If the c-string corresponding to the ConstantArray can
88 // be found successfully, see if it can be found in VarMap. If so, replace the
89 // uses of CallInst with the value found in VarMap. If not, replace the use
92 // The IR for __nvvm_reflect calls differs between CUDA versions.
94 // CUDA 6.5 and earlier uses this sequence:
95 // %ptr = tail call i8* @llvm.nvvm.ptr.constant.to.gen.p0i8.p4i8
96 // (i8 addrspace(4)* getelementptr inbounds
97 // ([8 x i8], [8 x i8] addrspace(4)* @str, i32 0, i32 0))
98 // %reflect = tail call i32 @__nvvm_reflect(i8* %ptr)
100 // The value returned by Sym->getOperand(0) is a Constant with a
101 // ConstantDataSequential operand which can be converted to string and used
104 // CUDA 7.0 does it slightly differently:
105 // %reflect = call i32 @__nvvm_reflect(i8* addrspacecast
106 // (i8 addrspace(1)* getelementptr inbounds
107 // ([8 x i8], [8 x i8] addrspace(1)* @str, i32 0, i32 0) to i8*))
109 // In this case, we get a Constant with a GlobalVariable operand and we need
110 // to dig deeper to find its initializer with the string we'll use for lookup.
111 for (Instruction &I : instructions(F)) {
112 CallInst *Call = dyn_cast<CallInst>(&I);
115 Function *Callee = Call->getCalledFunction();
116 if (!Callee || (Callee->getName() != NVVM_REFLECT_FUNCTION &&
117 Callee->getIntrinsicID() != Intrinsic::nvvm_reflect))
120 // FIXME: Improve error handling here and elsewhere in this pass.
121 assert(Call->getNumOperands() == 2 &&
122 "Wrong number of operands to __nvvm_reflect function");
124 // In cuda 6.5 and earlier, we will have an extra constant-to-generic
125 // conversion of the string.
126 const Value *Str = Call->getArgOperand(0);
127 if (const CallInst *ConvCall = dyn_cast<CallInst>(Str)) {
128 // FIXME: Add assertions about ConvCall.
129 Str = ConvCall->getArgOperand(0);
131 assert(isa<ConstantExpr>(Str) &&
132 "Format of __nvvm__reflect function not recognized");
133 const ConstantExpr *GEP = cast<ConstantExpr>(Str);
135 const Value *Sym = GEP->getOperand(0);
136 assert(isa<Constant>(Sym) &&
137 "Format of __nvvm_reflect function not recognized");
139 const Value *Operand = cast<Constant>(Sym)->getOperand(0);
140 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Operand)) {
141 // For CUDA-7.0 style __nvvm_reflect calls, we need to find the operand's
143 assert(GV->hasInitializer() &&
144 "Format of _reflect function not recognized");
145 const Constant *Initializer = GV->getInitializer();
146 Operand = Initializer;
149 assert(isa<ConstantDataSequential>(Operand) &&
150 "Format of _reflect function not recognized");
151 assert(cast<ConstantDataSequential>(Operand)->isCString() &&
152 "Format of _reflect function not recognized");
154 StringRef ReflectArg = cast<ConstantDataSequential>(Operand)->getAsString();
155 ReflectArg = ReflectArg.substr(0, ReflectArg.size() - 1);
156 LLVM_DEBUG(dbgs() << "Arg of _reflect : " << ReflectArg << "\n");
158 int ReflectVal = 0; // The default value is 0
159 if (ReflectArg == "__CUDA_FTZ") {
160 // Try to pull __CUDA_FTZ from the nvvm-reflect-ftz module flag. Our
161 // choice here must be kept in sync with AutoUpgrade, which uses the same
162 // technique to detect whether ftz is enabled.
163 if (auto *Flag = mdconst::extract_or_null<ConstantInt>(
164 F.getParent()->getModuleFlag("nvvm-reflect-ftz")))
165 ReflectVal = Flag->getSExtValue();
167 Call->replaceAllUsesWith(ConstantInt::get(Call->getType(), ReflectVal));
168 ToRemove.push_back(Call);
171 for (Instruction *I : ToRemove)
172 I->eraseFromParent();
174 return ToRemove.size() > 0;