1 //===- AMDGPUEmitPrintf.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 // Utility function to lower a printf call into a series of device
10 // library calls on the AMDGPU target.
11 //
12 // WARNING: This file knows about certain library functions. It recognizes them
13 // by name, and hardwires knowledge of their semantics.
14 //
15 //===----------------------------------------------------------------------===//
16
17 #include "llvm/Transforms/Utils/AMDGPUEmitPrintf.h"
18 #include "llvm/ADT/SparseBitVector.h"
19 #include "llvm/Analysis/ValueTracking.h"
20
21 using namespace llvm;
22
23 #define DEBUG_TYPE "amdgpu-emit-printf"
24
isCString(const Value * Arg)25 static bool isCString(const Value *Arg) {
26 auto Ty = Arg->getType();
27 auto PtrTy = dyn_cast<PointerType>(Ty);
28 if (!PtrTy)
29 return false;
30
31 auto IntTy = dyn_cast<IntegerType>(PtrTy->getElementType());
32 if (!IntTy)
33 return false;
34
35 return IntTy->getBitWidth() == 8;
36 }
37
fitArgInto64Bits(IRBuilder<> & Builder,Value * Arg)38 static Value *fitArgInto64Bits(IRBuilder<> &Builder, Value *Arg) {
39 auto Int64Ty = Builder.getInt64Ty();
40 auto Ty = Arg->getType();
41
42 if (auto IntTy = dyn_cast<IntegerType>(Ty)) {
43 switch (IntTy->getBitWidth()) {
44 case 32:
45 return Builder.CreateZExt(Arg, Int64Ty);
46 case 64:
47 return Arg;
48 }
49 }
50
51 if (Ty->getTypeID() == Type::DoubleTyID) {
52 return Builder.CreateBitCast(Arg, Int64Ty);
53 }
54
55 if (isa<PointerType>(Ty)) {
56 return Builder.CreatePtrToInt(Arg, Int64Ty);
57 }
58
59 llvm_unreachable("unexpected type");
60 }
61
callPrintfBegin(IRBuilder<> & Builder,Value * Version)62 static Value *callPrintfBegin(IRBuilder<> &Builder, Value *Version) {
63 auto Int64Ty = Builder.getInt64Ty();
64 auto M = Builder.GetInsertBlock()->getModule();
65 auto Fn = M->getOrInsertFunction("__ockl_printf_begin", Int64Ty, Int64Ty);
66 return Builder.CreateCall(Fn, Version);
67 }
68
callAppendArgs(IRBuilder<> & Builder,Value * Desc,int NumArgs,Value * Arg0,Value * Arg1,Value * Arg2,Value * Arg3,Value * Arg4,Value * Arg5,Value * Arg6,bool IsLast)69 static Value *callAppendArgs(IRBuilder<> &Builder, Value *Desc, int NumArgs,
70 Value *Arg0, Value *Arg1, Value *Arg2, Value *Arg3,
71 Value *Arg4, Value *Arg5, Value *Arg6,
72 bool IsLast) {
73 auto Int64Ty = Builder.getInt64Ty();
74 auto Int32Ty = Builder.getInt32Ty();
75 auto M = Builder.GetInsertBlock()->getModule();
76 auto Fn = M->getOrInsertFunction("__ockl_printf_append_args", Int64Ty,
77 Int64Ty, Int32Ty, Int64Ty, Int64Ty, Int64Ty,
78 Int64Ty, Int64Ty, Int64Ty, Int64Ty, Int32Ty);
79 auto IsLastValue = Builder.getInt32(IsLast);
80 auto NumArgsValue = Builder.getInt32(NumArgs);
81 return Builder.CreateCall(Fn, {Desc, NumArgsValue, Arg0, Arg1, Arg2, Arg3,
82 Arg4, Arg5, Arg6, IsLastValue});
83 }
84
appendArg(IRBuilder<> & Builder,Value * Desc,Value * Arg,bool IsLast)85 static Value *appendArg(IRBuilder<> &Builder, Value *Desc, Value *Arg,
86 bool IsLast) {
87 auto Arg0 = fitArgInto64Bits(Builder, Arg);
88 auto Zero = Builder.getInt64(0);
89 return callAppendArgs(Builder, Desc, 1, Arg0, Zero, Zero, Zero, Zero, Zero,
90 Zero, IsLast);
91 }
92
93 // The device library does not provide strlen, so we build our own loop
94 // here. While we are at it, we also include the terminating null in the length.
getStrlenWithNull(IRBuilder<> & Builder,Value * Str)95 static Value *getStrlenWithNull(IRBuilder<> &Builder, Value *Str) {
96 auto *Prev = Builder.GetInsertBlock();
97 Module *M = Prev->getModule();
98
99 auto CharZero = Builder.getInt8(0);
100 auto One = Builder.getInt64(1);
101 auto Zero = Builder.getInt64(0);
102 auto Int64Ty = Builder.getInt64Ty();
103
104 // The length is either zero for a null pointer, or the computed value for an
105 // actual string. We need a join block for a phi that represents the final
106 // value.
107 //
108 // Strictly speaking, the zero does not matter since
109 // __ockl_printf_append_string_n ignores the length if the pointer is null.
110 BasicBlock *Join = nullptr;
111 if (Prev->getTerminator()) {
112 Join = Prev->splitBasicBlock(Builder.GetInsertPoint(),
113 "strlen.join");
114 Prev->getTerminator()->eraseFromParent();
115 } else {
116 Join = BasicBlock::Create(M->getContext(), "strlen.join",
117 Prev->getParent());
118 }
119 BasicBlock *While =
120 BasicBlock::Create(M->getContext(), "strlen.while",
121 Prev->getParent(), Join);
122 BasicBlock *WhileDone = BasicBlock::Create(
123 M->getContext(), "strlen.while.done",
124 Prev->getParent(), Join);
125
126 // Emit an early return for when the pointer is null.
127 Builder.SetInsertPoint(Prev);
128 auto CmpNull =
129 Builder.CreateICmpEQ(Str, Constant::getNullValue(Str->getType()));
130 BranchInst::Create(Join, While, CmpNull, Prev);
131
132 // Entry to the while loop.
133 Builder.SetInsertPoint(While);
134
135 auto PtrPhi = Builder.CreatePHI(Str->getType(), 2);
136 PtrPhi->addIncoming(Str, Prev);
137 auto PtrNext = Builder.CreateGEP(PtrPhi, One);
138 PtrPhi->addIncoming(PtrNext, While);
139
140 // Condition for the while loop.
141 auto Data = Builder.CreateLoad(Builder.getInt8Ty(), PtrPhi);
142 auto Cmp = Builder.CreateICmpEQ(Data, CharZero);
143 Builder.CreateCondBr(Cmp, WhileDone, While);
144
145 // Add one to the computed length.
146 Builder.SetInsertPoint(WhileDone, WhileDone->begin());
147 auto Begin = Builder.CreatePtrToInt(Str, Int64Ty);
148 auto End = Builder.CreatePtrToInt(PtrPhi, Int64Ty);
149 auto Len = Builder.CreateSub(End, Begin);
150 Len = Builder.CreateAdd(Len, One);
151
152 // Final join.
153 BranchInst::Create(Join, WhileDone);
154 Builder.SetInsertPoint(Join, Join->begin());
155 auto LenPhi = Builder.CreatePHI(Len->getType(), 2);
156 LenPhi->addIncoming(Len, WhileDone);
157 LenPhi->addIncoming(Zero, Prev);
158
159 return LenPhi;
160 }
161
callAppendStringN(IRBuilder<> & Builder,Value * Desc,Value * Str,Value * Length,bool isLast)162 static Value *callAppendStringN(IRBuilder<> &Builder, Value *Desc, Value *Str,
163 Value *Length, bool isLast) {
164 auto Int64Ty = Builder.getInt64Ty();
165 auto CharPtrTy = Builder.getInt8PtrTy();
166 auto Int32Ty = Builder.getInt32Ty();
167 auto M = Builder.GetInsertBlock()->getModule();
168 auto Fn = M->getOrInsertFunction("__ockl_printf_append_string_n", Int64Ty,
169 Int64Ty, CharPtrTy, Int64Ty, Int32Ty);
170 auto IsLastInt32 = Builder.getInt32(isLast);
171 return Builder.CreateCall(Fn, {Desc, Str, Length, IsLastInt32});
172 }
173
appendString(IRBuilder<> & Builder,Value * Desc,Value * Arg,bool IsLast)174 static Value *appendString(IRBuilder<> &Builder, Value *Desc, Value *Arg,
175 bool IsLast) {
176 auto Length = getStrlenWithNull(Builder, Arg);
177 return callAppendStringN(Builder, Desc, Arg, Length, IsLast);
178 }
179
processArg(IRBuilder<> & Builder,Value * Desc,Value * Arg,bool SpecIsCString,bool IsLast)180 static Value *processArg(IRBuilder<> &Builder, Value *Desc, Value *Arg,
181 bool SpecIsCString, bool IsLast) {
182 if (SpecIsCString && isCString(Arg)) {
183 return appendString(Builder, Desc, Arg, IsLast);
184 }
185 // If the format specifies a string but the argument is not, the frontend will
186 // have printed a warning. We just rely on undefined behaviour and send the
187 // argument anyway.
188 return appendArg(Builder, Desc, Arg, IsLast);
189 }
190
191 // Scan the format string to locate all specifiers, and mark the ones that
192 // specify a string, i.e, the "%s" specifier with optional '*' characters.
locateCStrings(SparseBitVector<8> & BV,Value * Fmt)193 static void locateCStrings(SparseBitVector<8> &BV, Value *Fmt) {
194 StringRef Str;
195 if (!getConstantStringInfo(Fmt, Str) || Str.empty())
196 return;
197
198 static const char ConvSpecifiers[] = "diouxXfFeEgGaAcspn";
199 size_t SpecPos = 0;
200 // Skip the first argument, the format string.
201 unsigned ArgIdx = 1;
202
203 while ((SpecPos = Str.find_first_of('%', SpecPos)) != StringRef::npos) {
204 if (Str[SpecPos + 1] == '%') {
205 SpecPos += 2;
206 continue;
207 }
208 auto SpecEnd = Str.find_first_of(ConvSpecifiers, SpecPos);
209 if (SpecEnd == StringRef::npos)
210 return;
211 auto Spec = Str.slice(SpecPos, SpecEnd + 1);
212 ArgIdx += Spec.count('*');
213 if (Str[SpecEnd] == 's') {
214 BV.set(ArgIdx);
215 }
216 SpecPos = SpecEnd + 1;
217 ++ArgIdx;
218 }
219 }
220
emitAMDGPUPrintfCall(IRBuilder<> & Builder,ArrayRef<Value * > Args)221 Value *llvm::emitAMDGPUPrintfCall(IRBuilder<> &Builder,
222 ArrayRef<Value *> Args) {
223 auto NumOps = Args.size();
224 assert(NumOps >= 1);
225
226 auto Fmt = Args[0];
227 SparseBitVector<8> SpecIsCString;
228 locateCStrings(SpecIsCString, Fmt);
229
230 auto Desc = callPrintfBegin(Builder, Builder.getIntN(64, 0));
231 Desc = appendString(Builder, Desc, Fmt, NumOps == 1);
232
233 // FIXME: This invokes hostcall once for each argument. We can pack up to
234 // seven scalar printf arguments in a single hostcall. See the signature of
235 // callAppendArgs().
236 for (unsigned int i = 1; i != NumOps; ++i) {
237 bool IsLast = i == NumOps - 1;
238 bool IsCString = SpecIsCString.test(i);
239 Desc = processArg(Builder, Desc, Args[i], IsCString, IsLast);
240 }
241
242 return Builder.CreateTrunc(Desc, Builder.getInt32Ty());
243 }
244