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      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 "bcc/Renderscript/RSTransforms.h"
     18 #include "bcc/Renderscript/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 
     68   RSInvariantPass() : FunctionPass(ID), EmptyMDNode(nullptr) { }
     69 
     70   virtual bool doInitialization(llvm::Module &M) {
     71     EmptyMDNode = llvm::MDNode::get(M.getContext(), llvm::None);
     72     return true;
     73   }
     74 
     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 
     96   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    */
    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 *
    149 createRSInvariantPass() {
    150   return new RSInvariantPass();
    151 }
    152 
    153 } // end namespace bcc
    154