xref: /freebsd/contrib/llvm-project/llvm/lib/Target/AMDGPU/SIAnnotateControlFlow.cpp (revision e6bfd18d21b225af6a0ed67ceeaf1293b7b9eba5) 
1 //===- SIAnnotateControlFlow.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 /// \file
10 /// Annotates the control flow with hardware specific intrinsics.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "AMDGPU.h"
15 #include "GCNSubtarget.h"
16 #include "llvm/Analysis/LegacyDivergenceAnalysis.h"
17 #include "llvm/Analysis/LoopInfo.h"
18 #include "llvm/CodeGen/TargetPassConfig.h"
19 #include "llvm/IR/BasicBlock.h"
20 #include "llvm/IR/Constants.h"
21 #include "llvm/IR/Dominators.h"
22 #include "llvm/IR/IntrinsicsAMDGPU.h"
23 #include "llvm/InitializePasses.h"
24 #include "llvm/Target/TargetMachine.h"
25 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
26 #include "llvm/Transforms/Utils/Local.h"
27 
28 using namespace llvm;
29 
30 #define DEBUG_TYPE "si-annotate-control-flow"
31 
32 namespace {
33 
34 // Complex types used in this pass
35 using StackEntry = std::pair<BasicBlock *, Value *>;
36 using StackVector = SmallVector<StackEntry, 16>;
37 
38 class SIAnnotateControlFlow : public FunctionPass {
39   LegacyDivergenceAnalysis *DA;
40 
41   Type *Boolean;
42   Type *Void;
43   Type *IntMask;
44   Type *ReturnStruct;
45 
46   ConstantInt *BoolTrue;
47   ConstantInt *BoolFalse;
48   UndefValue *BoolUndef;
49   Constant *IntMaskZero;
50 
51   Function *If;
52   Function *Else;
53   Function *IfBreak;
54   Function *Loop;
55   Function *EndCf;
56 
57   DominatorTree *DT;
58   StackVector Stack;
59 
60   LoopInfo *LI;
61 
62   void initialize(Module &M, const GCNSubtarget &ST);
63 
64   bool isUniform(BranchInst *T);
65 
66   bool isTopOfStack(BasicBlock *BB);
67 
68   Value *popSaved();
69 
70   void push(BasicBlock *BB, Value *Saved);
71 
72   bool isElse(PHINode *Phi);
73 
74   bool hasKill(const BasicBlock *BB);
75 
76   bool eraseIfUnused(PHINode *Phi);
77 
78   bool openIf(BranchInst *Term);
79 
80   bool insertElse(BranchInst *Term);
81 
82   Value *
83   handleLoopCondition(Value *Cond, PHINode *Broken, llvm::Loop *L,
84                       BranchInst *Term);
85 
86   bool handleLoop(BranchInst *Term);
87 
88   bool closeControlFlow(BasicBlock *BB);
89 
90 public:
91   static char ID;
92 
93   SIAnnotateControlFlow() : FunctionPass(ID) {}
94 
95   bool runOnFunction(Function &F) override;
96 
97   StringRef getPassName() const override { return "SI annotate control flow"; }
98 
99   void getAnalysisUsage(AnalysisUsage &AU) const override {
100     AU.addRequired<LoopInfoWrapperPass>();
101     AU.addRequired<DominatorTreeWrapperPass>();
102     AU.addRequired<LegacyDivergenceAnalysis>();
103     AU.addPreserved<LoopInfoWrapperPass>();
104     AU.addPreserved<DominatorTreeWrapperPass>();
105     AU.addRequired<TargetPassConfig>();
106     FunctionPass::getAnalysisUsage(AU);
107   }
108 };
109 
110 } // end anonymous namespace
111 
112 INITIALIZE_PASS_BEGIN(SIAnnotateControlFlow, DEBUG_TYPE,
113                       "Annotate SI Control Flow", false, false)
114 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
115 INITIALIZE_PASS_DEPENDENCY(LegacyDivergenceAnalysis)
116 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
117 INITIALIZE_PASS_END(SIAnnotateControlFlow, DEBUG_TYPE,
118                     "Annotate SI Control Flow", false, false)
119 
120 char SIAnnotateControlFlow::ID = 0;
121 
122 /// Initialize all the types and constants used in the pass
123 void SIAnnotateControlFlow::initialize(Module &M, const GCNSubtarget &ST) {
124   LLVMContext &Context = M.getContext();
125 
126   Void = Type::getVoidTy(Context);
127   Boolean = Type::getInt1Ty(Context);
128   IntMask = ST.isWave32() ? Type::getInt32Ty(Context)
129                            : Type::getInt64Ty(Context);
130   ReturnStruct = StructType::get(Boolean, IntMask);
131 
132   BoolTrue = ConstantInt::getTrue(Context);
133   BoolFalse = ConstantInt::getFalse(Context);
134   BoolUndef = UndefValue::get(Boolean);
135   IntMaskZero = ConstantInt::get(IntMask, 0);
136 
137   If = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_if, { IntMask });
138   Else = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_else,
139                                    { IntMask, IntMask });
140   IfBreak = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_if_break,
141                                       { IntMask });
142   Loop = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_loop, { IntMask });
143   EndCf = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_end_cf, { IntMask });
144 }
145 
146 /// Is the branch condition uniform or did the StructurizeCFG pass
147 /// consider it as such?
148 bool SIAnnotateControlFlow::isUniform(BranchInst *T) {
149   return DA->isUniform(T) ||
150          T->getMetadata("structurizecfg.uniform") != nullptr;
151 }
152 
153 /// Is BB the last block saved on the stack ?
154 bool SIAnnotateControlFlow::isTopOfStack(BasicBlock *BB) {
155   return !Stack.empty() && Stack.back().first == BB;
156 }
157 
158 /// Pop the last saved value from the control flow stack
159 Value *SIAnnotateControlFlow::popSaved() {
160   return Stack.pop_back_val().second;
161 }
162 
163 /// Push a BB and saved value to the control flow stack
164 void SIAnnotateControlFlow::push(BasicBlock *BB, Value *Saved) {
165   Stack.push_back(std::make_pair(BB, Saved));
166 }
167 
168 /// Can the condition represented by this PHI node treated like
169 /// an "Else" block?
170 bool SIAnnotateControlFlow::isElse(PHINode *Phi) {
171   BasicBlock *IDom = DT->getNode(Phi->getParent())->getIDom()->getBlock();
172   for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
173     if (Phi->getIncomingBlock(i) == IDom) {
174 
175       if (Phi->getIncomingValue(i) != BoolTrue)
176         return false;
177 
178     } else {
179       if (Phi->getIncomingValue(i) != BoolFalse)
180         return false;
181 
182     }
183   }
184   return true;
185 }
186 
187 bool SIAnnotateControlFlow::hasKill(const BasicBlock *BB) {
188   for (const Instruction &I : *BB) {
189     if (const CallInst *CI = dyn_cast<CallInst>(&I))
190       if (CI->getIntrinsicID() == Intrinsic::amdgcn_kill)
191         return true;
192   }
193   return false;
194 }
195 
196 // Erase "Phi" if it is not used any more. Return true if any change was made.
197 bool SIAnnotateControlFlow::eraseIfUnused(PHINode *Phi) {
198   bool Changed = RecursivelyDeleteDeadPHINode(Phi);
199   if (Changed)
200     LLVM_DEBUG(dbgs() << "Erased unused condition phi\n");
201   return Changed;
202 }
203 
204 /// Open a new "If" block
205 bool SIAnnotateControlFlow::openIf(BranchInst *Term) {
206   if (isUniform(Term))
207     return false;
208 
209   Value *Ret = CallInst::Create(If, Term->getCondition(), "", Term);
210   Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
211   push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
212   return true;
213 }
214 
215 /// Close the last "If" block and open a new "Else" block
216 bool SIAnnotateControlFlow::insertElse(BranchInst *Term) {
217   if (isUniform(Term)) {
218     return false;
219   }
220   Value *Ret = CallInst::Create(Else, popSaved(), "", Term);
221   Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
222   push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
223   return true;
224 }
225 
226 /// Recursively handle the condition leading to a loop
227 Value *SIAnnotateControlFlow::handleLoopCondition(
228     Value *Cond, PHINode *Broken, llvm::Loop *L, BranchInst *Term) {
229   if (Instruction *Inst = dyn_cast<Instruction>(Cond)) {
230     BasicBlock *Parent = Inst->getParent();
231     Instruction *Insert;
232     if (L->contains(Inst)) {
233       Insert = Parent->getTerminator();
234     } else {
235       Insert = L->getHeader()->getFirstNonPHIOrDbgOrLifetime();
236     }
237 
238     Value *Args[] = { Cond, Broken };
239     return CallInst::Create(IfBreak, Args, "", Insert);
240   }
241 
242   // Insert IfBreak in the loop header TERM for constant COND other than true.
243   if (isa<Constant>(Cond)) {
244     Instruction *Insert = Cond == BoolTrue ?
245       Term : L->getHeader()->getTerminator();
246 
247     Value *Args[] = { Cond, Broken };
248     return CallInst::Create(IfBreak, Args, "", Insert);
249   }
250 
251   if (isa<Argument>(Cond)) {
252     Instruction *Insert = L->getHeader()->getFirstNonPHIOrDbgOrLifetime();
253     Value *Args[] = { Cond, Broken };
254     return CallInst::Create(IfBreak, Args, "", Insert);
255   }
256 
257   llvm_unreachable("Unhandled loop condition!");
258 }
259 
260 /// Handle a back edge (loop)
261 bool SIAnnotateControlFlow::handleLoop(BranchInst *Term) {
262   if (isUniform(Term))
263     return false;
264 
265   BasicBlock *BB = Term->getParent();
266   llvm::Loop *L = LI->getLoopFor(BB);
267   if (!L)
268     return false;
269 
270   BasicBlock *Target = Term->getSuccessor(1);
271   PHINode *Broken = PHINode::Create(IntMask, 0, "phi.broken", &Target->front());
272 
273   Value *Cond = Term->getCondition();
274   Term->setCondition(BoolTrue);
275   Value *Arg = handleLoopCondition(Cond, Broken, L, Term);
276 
277   for (BasicBlock *Pred : predecessors(Target)) {
278     Value *PHIValue = IntMaskZero;
279     if (Pred == BB) // Remember the value of the previous iteration.
280       PHIValue = Arg;
281     // If the backedge from Pred to Target could be executed before the exit
282     // of the loop at BB, it should not reset or change "Broken", which keeps
283     // track of the number of threads exited the loop at BB.
284     else if (L->contains(Pred) && DT->dominates(Pred, BB))
285       PHIValue = Broken;
286     Broken->addIncoming(PHIValue, Pred);
287   }
288 
289   Term->setCondition(CallInst::Create(Loop, Arg, "", Term));
290 
291   push(Term->getSuccessor(0), Arg);
292 
293   return true;
294 }
295 
296 /// Close the last opened control flow
297 bool SIAnnotateControlFlow::closeControlFlow(BasicBlock *BB) {
298   llvm::Loop *L = LI->getLoopFor(BB);
299 
300   assert(Stack.back().first == BB);
301 
302   if (L && L->getHeader() == BB) {
303     // We can't insert an EndCF call into a loop header, because it will
304     // get executed on every iteration of the loop, when it should be
305     // executed only once before the loop.
306     SmallVector <BasicBlock *, 8> Latches;
307     L->getLoopLatches(Latches);
308 
309     SmallVector<BasicBlock *, 2> Preds;
310     for (BasicBlock *Pred : predecessors(BB)) {
311       if (!is_contained(Latches, Pred))
312         Preds.push_back(Pred);
313     }
314 
315     BB = SplitBlockPredecessors(BB, Preds, "endcf.split", DT, LI, nullptr,
316                                 false);
317   }
318 
319   Value *Exec = popSaved();
320   Instruction *FirstInsertionPt = &*BB->getFirstInsertionPt();
321   if (!isa<UndefValue>(Exec) && !isa<UnreachableInst>(FirstInsertionPt)) {
322     Instruction *ExecDef = cast<Instruction>(Exec);
323     BasicBlock *DefBB = ExecDef->getParent();
324     if (!DT->dominates(DefBB, BB)) {
325       // Split edge to make Def dominate Use
326       FirstInsertionPt = &*SplitEdge(DefBB, BB, DT, LI)->getFirstInsertionPt();
327     }
328     CallInst::Create(EndCf, Exec, "", FirstInsertionPt);
329   }
330 
331   return true;
332 }
333 
334 /// Annotate the control flow with intrinsics so the backend can
335 /// recognize if/then/else and loops.
336 bool SIAnnotateControlFlow::runOnFunction(Function &F) {
337   DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
338   LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
339   DA = &getAnalysis<LegacyDivergenceAnalysis>();
340   TargetPassConfig &TPC = getAnalysis<TargetPassConfig>();
341   const TargetMachine &TM = TPC.getTM<TargetMachine>();
342 
343   bool Changed = false;
344   initialize(*F.getParent(), TM.getSubtarget<GCNSubtarget>(F));
345   for (df_iterator<BasicBlock *> I = df_begin(&F.getEntryBlock()),
346        E = df_end(&F.getEntryBlock()); I != E; ++I) {
347     BasicBlock *BB = *I;
348     BranchInst *Term = dyn_cast<BranchInst>(BB->getTerminator());
349 
350     if (!Term || Term->isUnconditional()) {
351       if (isTopOfStack(BB))
352         Changed |= closeControlFlow(BB);
353 
354       continue;
355     }
356 
357     if (I.nodeVisited(Term->getSuccessor(1))) {
358       if (isTopOfStack(BB))
359         Changed |= closeControlFlow(BB);
360 
361       if (DT->dominates(Term->getSuccessor(1), BB))
362         Changed |= handleLoop(Term);
363       continue;
364     }
365 
366     if (isTopOfStack(BB)) {
367       PHINode *Phi = dyn_cast<PHINode>(Term->getCondition());
368       if (Phi && Phi->getParent() == BB && isElse(Phi) && !hasKill(BB)) {
369         Changed |= insertElse(Term);
370         Changed |= eraseIfUnused(Phi);
371         continue;
372       }
373 
374       Changed |= closeControlFlow(BB);
375     }
376 
377     Changed |= openIf(Term);
378   }
379 
380   if (!Stack.empty()) {
381     // CFG was probably not structured.
382     report_fatal_error("failed to annotate CFG");
383   }
384 
385   return Changed;
386 }
387 
388 /// Create the annotation pass
389 FunctionPass *llvm::createSIAnnotateControlFlowPass() {
390   return new SIAnnotateControlFlow();
391 }
392