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377 lines
11 KiB
377 lines
11 KiB
//===- SIAnnotateControlFlow.cpp ------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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/// \file
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/// Annotates the control flow with hardware specific intrinsics.
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//
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//===----------------------------------------------------------------------===//
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#include "AMDGPU.h"
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#include "AMDGPUSubtarget.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/Analysis/LegacyDivergenceAnalysis.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/CodeGen/TargetPassConfig.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/CFG.h"
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#include "llvm/IR/Constant.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DerivedTypes.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/Instruction.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/Intrinsics.h"
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#include "llvm/IR/Module.h"
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#include "llvm/IR/Type.h"
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#include "llvm/IR/ValueHandle.h"
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#include "llvm/InitializePasses.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include <cassert>
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#include <utility>
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using namespace llvm;
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#define DEBUG_TYPE "si-annotate-control-flow"
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namespace {
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// Complex types used in this pass
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using StackEntry = std::pair<BasicBlock *, Value *>;
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using StackVector = SmallVector<StackEntry, 16>;
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class SIAnnotateControlFlow : public FunctionPass {
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LegacyDivergenceAnalysis *DA;
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Type *Boolean;
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Type *Void;
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Type *IntMask;
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Type *ReturnStruct;
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ConstantInt *BoolTrue;
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ConstantInt *BoolFalse;
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UndefValue *BoolUndef;
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Constant *IntMaskZero;
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Function *If;
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Function *Else;
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Function *IfBreak;
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Function *Loop;
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Function *EndCf;
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DominatorTree *DT;
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StackVector Stack;
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LoopInfo *LI;
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void initialize(Module &M, const GCNSubtarget &ST);
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bool isUniform(BranchInst *T);
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bool isTopOfStack(BasicBlock *BB);
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Value *popSaved();
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void push(BasicBlock *BB, Value *Saved);
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bool isElse(PHINode *Phi);
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void eraseIfUnused(PHINode *Phi);
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void openIf(BranchInst *Term);
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void insertElse(BranchInst *Term);
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Value *
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handleLoopCondition(Value *Cond, PHINode *Broken, llvm::Loop *L,
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BranchInst *Term);
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void handleLoop(BranchInst *Term);
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void closeControlFlow(BasicBlock *BB);
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public:
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static char ID;
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SIAnnotateControlFlow() : FunctionPass(ID) {}
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bool runOnFunction(Function &F) override;
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StringRef getPassName() const override { return "SI annotate control flow"; }
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addRequired<LoopInfoWrapperPass>();
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AU.addRequired<DominatorTreeWrapperPass>();
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AU.addRequired<LegacyDivergenceAnalysis>();
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AU.addPreserved<DominatorTreeWrapperPass>();
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AU.addRequired<TargetPassConfig>();
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FunctionPass::getAnalysisUsage(AU);
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}
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};
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} // end anonymous namespace
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INITIALIZE_PASS_BEGIN(SIAnnotateControlFlow, DEBUG_TYPE,
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"Annotate SI Control Flow", false, false)
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INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(LegacyDivergenceAnalysis)
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INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
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INITIALIZE_PASS_END(SIAnnotateControlFlow, DEBUG_TYPE,
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"Annotate SI Control Flow", false, false)
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char SIAnnotateControlFlow::ID = 0;
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/// Initialize all the types and constants used in the pass
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void SIAnnotateControlFlow::initialize(Module &M, const GCNSubtarget &ST) {
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LLVMContext &Context = M.getContext();
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Void = Type::getVoidTy(Context);
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Boolean = Type::getInt1Ty(Context);
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IntMask = ST.isWave32() ? Type::getInt32Ty(Context)
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: Type::getInt64Ty(Context);
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ReturnStruct = StructType::get(Boolean, IntMask);
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BoolTrue = ConstantInt::getTrue(Context);
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BoolFalse = ConstantInt::getFalse(Context);
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BoolUndef = UndefValue::get(Boolean);
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IntMaskZero = ConstantInt::get(IntMask, 0);
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If = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_if, { IntMask });
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Else = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_else,
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{ IntMask, IntMask });
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IfBreak = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_if_break,
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{ IntMask });
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Loop = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_loop, { IntMask });
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EndCf = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_end_cf, { IntMask });
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}
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/// Is the branch condition uniform or did the StructurizeCFG pass
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/// consider it as such?
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bool SIAnnotateControlFlow::isUniform(BranchInst *T) {
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return DA->isUniform(T) ||
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T->getMetadata("structurizecfg.uniform") != nullptr;
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}
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/// Is BB the last block saved on the stack ?
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bool SIAnnotateControlFlow::isTopOfStack(BasicBlock *BB) {
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return !Stack.empty() && Stack.back().first == BB;
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}
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/// Pop the last saved value from the control flow stack
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Value *SIAnnotateControlFlow::popSaved() {
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return Stack.pop_back_val().second;
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}
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/// Push a BB and saved value to the control flow stack
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void SIAnnotateControlFlow::push(BasicBlock *BB, Value *Saved) {
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Stack.push_back(std::make_pair(BB, Saved));
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}
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/// Can the condition represented by this PHI node treated like
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/// an "Else" block?
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bool SIAnnotateControlFlow::isElse(PHINode *Phi) {
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BasicBlock *IDom = DT->getNode(Phi->getParent())->getIDom()->getBlock();
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for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
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if (Phi->getIncomingBlock(i) == IDom) {
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if (Phi->getIncomingValue(i) != BoolTrue)
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return false;
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} else {
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if (Phi->getIncomingValue(i) != BoolFalse)
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return false;
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}
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}
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return true;
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}
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// Erase "Phi" if it is not used any more
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void SIAnnotateControlFlow::eraseIfUnused(PHINode *Phi) {
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if (RecursivelyDeleteDeadPHINode(Phi)) {
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LLVM_DEBUG(dbgs() << "Erased unused condition phi\n");
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}
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}
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/// Open a new "If" block
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void SIAnnotateControlFlow::openIf(BranchInst *Term) {
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if (isUniform(Term))
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return;
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Value *Ret = CallInst::Create(If, Term->getCondition(), "", Term);
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Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
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push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
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}
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/// Close the last "If" block and open a new "Else" block
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void SIAnnotateControlFlow::insertElse(BranchInst *Term) {
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if (isUniform(Term)) {
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return;
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}
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Value *Ret = CallInst::Create(Else, popSaved(), "", Term);
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Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
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push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
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}
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/// Recursively handle the condition leading to a loop
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Value *SIAnnotateControlFlow::handleLoopCondition(
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Value *Cond, PHINode *Broken, llvm::Loop *L, BranchInst *Term) {
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if (Instruction *Inst = dyn_cast<Instruction>(Cond)) {
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BasicBlock *Parent = Inst->getParent();
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Instruction *Insert;
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if (L->contains(Inst)) {
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Insert = Parent->getTerminator();
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} else {
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Insert = L->getHeader()->getFirstNonPHIOrDbgOrLifetime();
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}
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Value *Args[] = { Cond, Broken };
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return CallInst::Create(IfBreak, Args, "", Insert);
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}
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// Insert IfBreak in the loop header TERM for constant COND other than true.
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if (isa<Constant>(Cond)) {
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Instruction *Insert = Cond == BoolTrue ?
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Term : L->getHeader()->getTerminator();
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Value *Args[] = { Cond, Broken };
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return CallInst::Create(IfBreak, Args, "", Insert);
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}
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llvm_unreachable("Unhandled loop condition!");
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}
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/// Handle a back edge (loop)
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void SIAnnotateControlFlow::handleLoop(BranchInst *Term) {
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if (isUniform(Term))
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return;
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BasicBlock *BB = Term->getParent();
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llvm::Loop *L = LI->getLoopFor(BB);
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if (!L)
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return;
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BasicBlock *Target = Term->getSuccessor(1);
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PHINode *Broken = PHINode::Create(IntMask, 0, "phi.broken", &Target->front());
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Value *Cond = Term->getCondition();
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Term->setCondition(BoolTrue);
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Value *Arg = handleLoopCondition(Cond, Broken, L, Term);
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for (BasicBlock *Pred : predecessors(Target)) {
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Value *PHIValue = IntMaskZero;
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if (Pred == BB) // Remember the value of the previous iteration.
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PHIValue = Arg;
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// If the backedge from Pred to Target could be executed before the exit
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// of the loop at BB, it should not reset or change "Broken", which keeps
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// track of the number of threads exited the loop at BB.
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else if (L->contains(Pred) && DT->dominates(Pred, BB))
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PHIValue = Broken;
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Broken->addIncoming(PHIValue, Pred);
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}
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Term->setCondition(CallInst::Create(Loop, Arg, "", Term));
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push(Term->getSuccessor(0), Arg);
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}
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/// Close the last opened control flow
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void SIAnnotateControlFlow::closeControlFlow(BasicBlock *BB) {
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llvm::Loop *L = LI->getLoopFor(BB);
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assert(Stack.back().first == BB);
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if (L && L->getHeader() == BB) {
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// We can't insert an EndCF call into a loop header, because it will
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// get executed on every iteration of the loop, when it should be
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// executed only once before the loop.
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SmallVector <BasicBlock *, 8> Latches;
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L->getLoopLatches(Latches);
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SmallVector<BasicBlock *, 2> Preds;
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for (BasicBlock *Pred : predecessors(BB)) {
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if (!is_contained(Latches, Pred))
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Preds.push_back(Pred);
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}
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BB = SplitBlockPredecessors(BB, Preds, "endcf.split", DT, LI, nullptr,
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false);
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}
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Value *Exec = popSaved();
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Instruction *FirstInsertionPt = &*BB->getFirstInsertionPt();
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if (!isa<UndefValue>(Exec) && !isa<UnreachableInst>(FirstInsertionPt))
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CallInst::Create(EndCf, Exec, "", FirstInsertionPt);
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}
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/// Annotate the control flow with intrinsics so the backend can
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/// recognize if/then/else and loops.
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bool SIAnnotateControlFlow::runOnFunction(Function &F) {
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DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
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LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
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DA = &getAnalysis<LegacyDivergenceAnalysis>();
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TargetPassConfig &TPC = getAnalysis<TargetPassConfig>();
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const TargetMachine &TM = TPC.getTM<TargetMachine>();
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initialize(*F.getParent(), TM.getSubtarget<GCNSubtarget>(F));
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for (df_iterator<BasicBlock *> I = df_begin(&F.getEntryBlock()),
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E = df_end(&F.getEntryBlock()); I != E; ++I) {
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BasicBlock *BB = *I;
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BranchInst *Term = dyn_cast<BranchInst>(BB->getTerminator());
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if (!Term || Term->isUnconditional()) {
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if (isTopOfStack(BB))
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closeControlFlow(BB);
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continue;
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}
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if (I.nodeVisited(Term->getSuccessor(1))) {
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if (isTopOfStack(BB))
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closeControlFlow(BB);
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handleLoop(Term);
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continue;
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}
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if (isTopOfStack(BB)) {
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PHINode *Phi = dyn_cast<PHINode>(Term->getCondition());
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if (Phi && Phi->getParent() == BB && isElse(Phi)) {
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insertElse(Term);
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eraseIfUnused(Phi);
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continue;
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}
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closeControlFlow(BB);
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}
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openIf(Term);
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}
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if (!Stack.empty()) {
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// CFG was probably not structured.
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report_fatal_error("failed to annotate CFG");
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}
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return true;
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}
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/// Create the annotation pass
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FunctionPass *llvm::createSIAnnotateControlFlowPass() {
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return new SIAnnotateControlFlow();
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}
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