xref: /freebsd/contrib/llvm-project/llvm/lib/Target/AMDGPU/SIAnnotateControlFlow.cpp (revision 7fdf597e96a02165cfe22ff357b857d5fa15ed8a) 
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/LoopInfo.h"
17 #include "llvm/Analysis/UniformityAnalysis.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/IRBuilder.h"
23 #include "llvm/IR/IntrinsicsAMDGPU.h"
24 #include "llvm/InitializePasses.h"
25 #include "llvm/Target/TargetMachine.h"
26 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
27 #include "llvm/Transforms/Utils/Local.h"
28 
29 using namespace llvm;
30 
31 #define DEBUG_TYPE "si-annotate-control-flow"
32 
33 namespace {
34 
35 // Complex types used in this pass
36 using StackEntry = std::pair<BasicBlock *, Value *>;
37 using StackVector = SmallVector<StackEntry, 16>;
38 
39 class SIAnnotateControlFlow : public FunctionPass {
40   UniformityInfo *UA;
41 
42   Type *Boolean;
43   Type *Void;
44   Type *IntMask;
45   Type *ReturnStruct;
46 
47   ConstantInt *BoolTrue;
48   ConstantInt *BoolFalse;
49   UndefValue *BoolUndef;
50   Constant *IntMaskZero;
51 
52   Function *If;
53   Function *Else;
54   Function *IfBreak;
55   Function *Loop;
56   Function *EndCf;
57 
58   DominatorTree *DT;
59   StackVector Stack;
60 
61   LoopInfo *LI;
62 
63   void initialize(Module &M, const GCNSubtarget &ST);
64 
65   bool isUniform(BranchInst *T);
66 
67   bool isTopOfStack(BasicBlock *BB);
68 
69   Value *popSaved();
70 
71   void push(BasicBlock *BB, Value *Saved);
72 
73   bool isElse(PHINode *Phi);
74 
75   bool hasKill(const BasicBlock *BB);
76 
77   bool eraseIfUnused(PHINode *Phi);
78 
79   bool openIf(BranchInst *Term);
80 
81   bool insertElse(BranchInst *Term);
82 
83   Value *
84   handleLoopCondition(Value *Cond, PHINode *Broken, llvm::Loop *L,
85                       BranchInst *Term);
86 
87   bool handleLoop(BranchInst *Term);
88 
89   bool closeControlFlow(BasicBlock *BB);
90 
91 public:
92   static char ID;
93 
94   SIAnnotateControlFlow() : FunctionPass(ID) {}
95 
96   bool runOnFunction(Function &F) override;
97 
98   StringRef getPassName() const override { return "SI annotate control flow"; }
99 
100   void getAnalysisUsage(AnalysisUsage &AU) const override {
101     AU.addRequired<LoopInfoWrapperPass>();
102     AU.addRequired<DominatorTreeWrapperPass>();
103     AU.addRequired<UniformityInfoWrapperPass>();
104     AU.addPreserved<LoopInfoWrapperPass>();
105     AU.addPreserved<DominatorTreeWrapperPass>();
106     AU.addRequired<TargetPassConfig>();
107     FunctionPass::getAnalysisUsage(AU);
108   }
109 };
110 
111 } // end anonymous namespace
112 
113 INITIALIZE_PASS_BEGIN(SIAnnotateControlFlow, DEBUG_TYPE,
114                       "Annotate SI Control Flow", false, false)
115 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
116 INITIALIZE_PASS_DEPENDENCY(UniformityInfoWrapperPass)
117 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
118 INITIALIZE_PASS_END(SIAnnotateControlFlow, DEBUG_TYPE,
119                     "Annotate SI Control Flow", false, false)
120 
121 char SIAnnotateControlFlow::ID = 0;
122 
123 /// Initialize all the types and constants used in the pass
124 void SIAnnotateControlFlow::initialize(Module &M, const GCNSubtarget &ST) {
125   LLVMContext &Context = M.getContext();
126 
127   Void = Type::getVoidTy(Context);
128   Boolean = Type::getInt1Ty(Context);
129   IntMask = ST.isWave32() ? Type::getInt32Ty(Context)
130                            : Type::getInt64Ty(Context);
131   ReturnStruct = StructType::get(Boolean, IntMask);
132 
133   BoolTrue = ConstantInt::getTrue(Context);
134   BoolFalse = ConstantInt::getFalse(Context);
135   BoolUndef = PoisonValue::get(Boolean);
136   IntMaskZero = ConstantInt::get(IntMask, 0);
137 
138   If = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_if, { IntMask });
139   Else = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_else,
140                                    { IntMask, IntMask });
141   IfBreak = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_if_break,
142                                       { IntMask });
143   Loop = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_loop, { IntMask });
144   EndCf = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_end_cf, { IntMask });
145 }
146 
147 /// Is the branch condition uniform or did the StructurizeCFG pass
148 /// consider it as such?
149 bool SIAnnotateControlFlow::isUniform(BranchInst *T) {
150   return UA->isUniform(T) || T->hasMetadata("structurizecfg.uniform");
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::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   IRBuilder<> IRB(Term);
210   Value *IfCall = IRB.CreateCall(If, {Term->getCondition()});
211   Value *Cond = IRB.CreateExtractValue(IfCall, {0});
212   Value *Mask = IRB.CreateExtractValue(IfCall, {1});
213   Term->setCondition(Cond);
214   push(Term->getSuccessor(1), Mask);
215   return true;
216 }
217 
218 /// Close the last "If" block and open a new "Else" block
219 bool SIAnnotateControlFlow::insertElse(BranchInst *Term) {
220   if (isUniform(Term)) {
221     return false;
222   }
223 
224   IRBuilder<> IRB(Term);
225   Value *ElseCall = IRB.CreateCall(Else, {popSaved()});
226   Value *Cond = IRB.CreateExtractValue(ElseCall, {0});
227   Value *Mask = IRB.CreateExtractValue(ElseCall, {1});
228   Term->setCondition(Cond);
229   push(Term->getSuccessor(1), Mask);
230   return true;
231 }
232 
233 /// Recursively handle the condition leading to a loop
234 Value *SIAnnotateControlFlow::handleLoopCondition(
235     Value *Cond, PHINode *Broken, llvm::Loop *L, BranchInst *Term) {
236 
237   auto CreateBreak = [this, Cond, Broken](Instruction *I) -> CallInst * {
238     return IRBuilder<>(I).CreateCall(IfBreak, {Cond, Broken});
239   };
240 
241   if (Instruction *Inst = dyn_cast<Instruction>(Cond)) {
242     BasicBlock *Parent = Inst->getParent();
243     Instruction *Insert;
244     if (L->contains(Inst)) {
245       Insert = Parent->getTerminator();
246     } else {
247       Insert = L->getHeader()->getFirstNonPHIOrDbgOrLifetime();
248     }
249 
250     return CreateBreak(Insert);
251   }
252 
253   // Insert IfBreak in the loop header TERM for constant COND other than true.
254   if (isa<Constant>(Cond)) {
255     Instruction *Insert = Cond == BoolTrue ?
256       Term : L->getHeader()->getTerminator();
257 
258     return CreateBreak(Insert);
259   }
260 
261   if (isa<Argument>(Cond)) {
262     Instruction *Insert = L->getHeader()->getFirstNonPHIOrDbgOrLifetime();
263     return CreateBreak(Insert);
264   }
265 
266   llvm_unreachable("Unhandled loop condition!");
267 }
268 
269 /// Handle a back edge (loop)
270 bool SIAnnotateControlFlow::handleLoop(BranchInst *Term) {
271   if (isUniform(Term))
272     return false;
273 
274   BasicBlock *BB = Term->getParent();
275   llvm::Loop *L = LI->getLoopFor(BB);
276   if (!L)
277     return false;
278 
279   BasicBlock *Target = Term->getSuccessor(1);
280   PHINode *Broken = PHINode::Create(IntMask, 0, "phi.broken");
281   Broken->insertBefore(Target->begin());
282 
283   Value *Cond = Term->getCondition();
284   Term->setCondition(BoolTrue);
285   Value *Arg = handleLoopCondition(Cond, Broken, L, Term);
286 
287   for (BasicBlock *Pred : predecessors(Target)) {
288     Value *PHIValue = IntMaskZero;
289     if (Pred == BB) // Remember the value of the previous iteration.
290       PHIValue = Arg;
291     // If the backedge from Pred to Target could be executed before the exit
292     // of the loop at BB, it should not reset or change "Broken", which keeps
293     // track of the number of threads exited the loop at BB.
294     else if (L->contains(Pred) && DT->dominates(Pred, BB))
295       PHIValue = Broken;
296     Broken->addIncoming(PHIValue, Pred);
297   }
298 
299   CallInst *LoopCall = IRBuilder<>(Term).CreateCall(Loop, {Arg});
300   Term->setCondition(LoopCall);
301 
302   push(Term->getSuccessor(0), Arg);
303 
304   return true;
305 }
306 
307 /// Close the last opened control flow
308 bool SIAnnotateControlFlow::closeControlFlow(BasicBlock *BB) {
309   llvm::Loop *L = LI->getLoopFor(BB);
310 
311   assert(Stack.back().first == BB);
312 
313   if (L && L->getHeader() == BB) {
314     // We can't insert an EndCF call into a loop header, because it will
315     // get executed on every iteration of the loop, when it should be
316     // executed only once before the loop.
317     SmallVector <BasicBlock *, 8> Latches;
318     L->getLoopLatches(Latches);
319 
320     SmallVector<BasicBlock *, 2> Preds;
321     for (BasicBlock *Pred : predecessors(BB)) {
322       if (!is_contained(Latches, Pred))
323         Preds.push_back(Pred);
324     }
325 
326     BB = SplitBlockPredecessors(BB, Preds, "endcf.split", DT, LI, nullptr,
327                                 false);
328   }
329 
330   Value *Exec = popSaved();
331   BasicBlock::iterator FirstInsertionPt = BB->getFirstInsertionPt();
332   if (!isa<UndefValue>(Exec) && !isa<UnreachableInst>(FirstInsertionPt)) {
333     Instruction *ExecDef = cast<Instruction>(Exec);
334     BasicBlock *DefBB = ExecDef->getParent();
335     if (!DT->dominates(DefBB, BB)) {
336       // Split edge to make Def dominate Use
337       FirstInsertionPt = SplitEdge(DefBB, BB, DT, LI)->getFirstInsertionPt();
338     }
339     IRBuilder<> IRB(FirstInsertionPt->getParent(), FirstInsertionPt);
340     // TODO: StructurizeCFG 'Flow' blocks have debug locations from the
341     // condition, for now just avoid copying these DebugLocs so that stepping
342     // out of the then/else block in a debugger doesn't step to the condition.
343     IRB.SetCurrentDebugLocation(DebugLoc());
344     IRB.CreateCall(EndCf, {Exec});
345   }
346 
347   return true;
348 }
349 
350 /// Annotate the control flow with intrinsics so the backend can
351 /// recognize if/then/else and loops.
352 bool SIAnnotateControlFlow::runOnFunction(Function &F) {
353   DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
354   LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
355   UA = &getAnalysis<UniformityInfoWrapperPass>().getUniformityInfo();
356   TargetPassConfig &TPC = getAnalysis<TargetPassConfig>();
357   const TargetMachine &TM = TPC.getTM<TargetMachine>();
358 
359   bool Changed = false;
360   initialize(*F.getParent(), TM.getSubtarget<GCNSubtarget>(F));
361   for (df_iterator<BasicBlock *> I = df_begin(&F.getEntryBlock()),
362        E = df_end(&F.getEntryBlock()); I != E; ++I) {
363     BasicBlock *BB = *I;
364     BranchInst *Term = dyn_cast<BranchInst>(BB->getTerminator());
365 
366     if (!Term || Term->isUnconditional()) {
367       if (isTopOfStack(BB))
368         Changed |= closeControlFlow(BB);
369 
370       continue;
371     }
372 
373     if (I.nodeVisited(Term->getSuccessor(1))) {
374       if (isTopOfStack(BB))
375         Changed |= closeControlFlow(BB);
376 
377       if (DT->dominates(Term->getSuccessor(1), BB))
378         Changed |= handleLoop(Term);
379       continue;
380     }
381 
382     if (isTopOfStack(BB)) {
383       PHINode *Phi = dyn_cast<PHINode>(Term->getCondition());
384       if (Phi && Phi->getParent() == BB && isElse(Phi) && !hasKill(BB)) {
385         Changed |= insertElse(Term);
386         Changed |= eraseIfUnused(Phi);
387         continue;
388       }
389 
390       Changed |= closeControlFlow(BB);
391     }
392 
393     Changed |= openIf(Term);
394   }
395 
396   if (!Stack.empty()) {
397     // CFG was probably not structured.
398     report_fatal_error("failed to annotate CFG");
399   }
400 
401   return Changed;
402 }
403 
404 /// Create the annotation pass
405 FunctionPass *llvm::createSIAnnotateControlFlowPass() {
406   return new SIAnnotateControlFlow();
407 }
408