1 /*
2 * Copyright 2015, The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include "RSTransforms.h"
18 #include "RSUtils.h"
19
20 #include <llvm/IR/Function.h>
21 #include <llvm/IR/Instructions.h>
22 #include <llvm/IR/Metadata.h>
23 #include <llvm/IR/Module.h>
24 #include <llvm/IR/Type.h>
25 #include <llvm/Pass.h>
26
27 namespace {
28
29 /*
30 * RSInvariantPass - This pass looks for Loads that access
31 * RsExpandKernelDriverInfo instances (which should never be written by
32 * a script, only by the driver) and marks them "invariant.load".
33 *
34 * There should be only two sources of Loads from such instances:
35 * - An instance can appear as an argument of type
36 * "RsExpandKernelDriverInfoPfx*" passed to a .expand function by
37 * the driver.
38 * - An instance can appear as an argument of type
39 * "rs_kernel_context_t*" passed to an API query function by the
40 * user.
41 * Only the compiler-generated .expand functions and the API query
42 * functions can see the fields of RsExpandKernelDriverInfo --
43 * rs_kernel_context_t is opaque to user code, so there cannot be any
44 * Loads from it in user code.
45 *
46 * This pass should be run
47 * - after foreachexp, so that it can see the Loads generated within
48 * .expand functions
49 * - before inlining, so that it can recognize API query function
50 * arguments.
51 *
52 * WARNINGS:
53 * - If user code or APIs can modify RsExpandKernelDriverInfo
54 * instances, this pass MAY ALLOW ILLEGAL OPTIMIZATION.
55 * - If this pass runs at a different time, it may be ineffective
56 * (fail to mark some or all eligible Loads, and thereby cost
57 * performance).
58 * - If the names of the data types change, this pass may be
59 * ineffective.
60 * - If the patterns by which fields are loaded from
61 * RsExpandKernelDriverInfo instances change, this pass may be
62 * ineffective.
63 */
64 class RSInvariantPass : public llvm::FunctionPass {
65 public:
66 static char ID;
67
RSInvariantPass()68 RSInvariantPass() : FunctionPass(ID), EmptyMDNode(nullptr) { }
69
doInitialization(llvm::Module & M)70 virtual bool doInitialization(llvm::Module &M) {
71 EmptyMDNode = llvm::MDNode::get(M.getContext(), llvm::None);
72 return true;
73 }
74
runOnFunction(llvm::Function & F)75 virtual bool runOnFunction(llvm::Function &F) {
76 bool Changed = false;
77
78 for (llvm::Value &Arg : F.args()) {
79 const llvm::Type *ArgType = Arg.getType();
80 if (ArgType->isPointerTy()) {
81 const llvm::Type *ArgPtrDomainType = ArgType->getPointerElementType();
82 if (auto ArgPtrDomainStructType = llvm::dyn_cast<llvm::StructType>(ArgPtrDomainType)) {
83 if (!ArgPtrDomainStructType->isLiteral()) {
84 const llvm::StringRef StructName = getUnsuffixedStructName(ArgPtrDomainStructType);
85 if (StructName.equals("struct.rs_kernel_context_t") || StructName.equals("RsExpandKernelDriverInfoPfx")) {
86 Changed |= markInvariantUserLoads(&Arg);
87 }
88 }
89 }
90 }
91 }
92
93 return Changed;
94 }
95
getPassName() const96 virtual const char *getPassName() const {
97 return "Renderscript Invariant Load Annotation";
98 }
99
100 private:
101
102 /*
103 * Follow def->use chains rooted at Value through calculations
104 * "based on" Value (see the "based on" definition at
105 * http://llvm.org/docs/LangRef.html#pointer-aliasing-rules). If a
106 * chain reaches the pointer operand of a Load, mark that Load as
107 * "invariant.load" -- i.e., it accesses memory which does not
108 * change.
109 */
markInvariantUserLoads(llvm::Value * Value)110 bool markInvariantUserLoads(llvm::Value *Value) {
111 bool Changed = false;
112 for (llvm::Use &Use : Value->uses()) {
113 llvm::Instruction *Inst = llvm::cast<llvm::Instruction>(Use.getUser());
114
115 /*
116 * We only examine a small set of opcodes here, because these
117 * are the opcodes that currently appear in the patterns of
118 * interest (foreachexp-generated code, and
119 * rsGet*(rs_kernel_context_t*) APIs). Other opcodes could be
120 * added if necessary.
121 */
122 if (auto BitCast = llvm::dyn_cast<llvm::BitCastInst>(Inst)) {
123 Changed |= markInvariantUserLoads(BitCast);
124 } else if (auto GetElementPtr = llvm::dyn_cast<llvm::GetElementPtrInst>(Inst)) {
125 if (Use.get() == GetElementPtr->getPointerOperand())
126 Changed |= markInvariantUserLoads(GetElementPtr);
127 } else if (auto Load = llvm::dyn_cast<llvm::LoadInst>(Inst)) {
128 if (Use.get() == Load->getPointerOperand()) {
129 Load->setMetadata("invariant.load", EmptyMDNode);
130 Changed = true;
131 }
132 }
133 }
134 return Changed;
135 }
136
137 // Pointer to empty metadata node used for "invariant.load" marking.
138 llvm::MDNode *EmptyMDNode;
139 }; // end RSInvariantPass
140
141 char RSInvariantPass::ID = 0;
142 llvm::RegisterPass<RSInvariantPass> X("rsinvariant", "RS Invariant Load Pass");
143
144 } // end anonymous namespace
145
146 namespace bcc {
147
148 llvm::FunctionPass *
createRSInvariantPass()149 createRSInvariantPass() {
150 return new RSInvariantPass();
151 }
152
153 } // end namespace bcc
154