return true;
}
-// Return true if V0 and V1 are equivalent. This handles the obvious cases
-// where V0 == V1 and V0 and V1 are both identical instructions, but also
-// handles loads and stores with identical operands.
-//
-// Because determining if two memory instructions are equivalent
-// depends on control flow, the \c At0 and \c At1 parameters specify a
-// location for the query. This function is essentially answering the
-// query "If V0 were moved to At0, and V1 were moved to At1, are V0 and V1
-// equivalent?". In practice this means checking that moving V0 to At0
-// doesn't cross any other memory instructions.
-static bool areValuesTriviallySame(Value *V0, BasicBlock::const_iterator At0,
- Value *V1, BasicBlock::const_iterator At1) {
- if (V0 == V1)
- return true;
-
- // Also check for instructions that are identical but not pointer-identical.
- // This can include load instructions that haven't been CSE'd.
- if (!isa<Instruction>(V0) || !isa<Instruction>(V1))
- return false;
- const auto *I0 = cast<Instruction>(V0);
- const auto *I1 = cast<Instruction>(V1);
- if (!I0->isIdenticalToWhenDefined(I1))
- return false;
-
- if (!I0->mayReadOrWriteMemory())
- return true;
+/// Given an unconditional branch that goes to BBEnd,
+/// check whether BBEnd has only two predecessors and the other predecessor
+/// ends with an unconditional branch. If it is true, sink any common code
+/// in the two predecessors to BBEnd.
+static bool SinkThenElseCodeToEnd(BranchInst *BI1) {
+ assert(BI1->isUnconditional());
+ BasicBlock *BB1 = BI1->getParent();
+ BasicBlock *BBEnd = BI1->getSuccessor(0);
- // Instructions that may read or write memory have extra restrictions. We
- // must ensure we don't treat %a and %b as equivalent in code such as:
- //
- // %a = load %x
- // store %x, 1
- // if (%c) {
- // %b = load %x
- // %d = add %b, 1
- // } else {
- // %d = add %a, 1
- // }
-
- // Be conservative. We don't want to search the entire CFG between def
- // and use; if the def isn't in the same block as the use just bail.
- if (I0->getParent() != At0->getParent() ||
- I1->getParent() != At1->getParent())
+ // Check that BBEnd has two predecessors and the other predecessor ends with
+ // an unconditional branch.
+ pred_iterator PI = pred_begin(BBEnd), PE = pred_end(BBEnd);
+ BasicBlock *Pred0 = *PI++;
+ if (PI == PE) // Only one predecessor.
return false;
-
- // Again, be super conservative. Ideally we'd be able to query AliasAnalysis
- // but we currently don't have that available.
- auto WritesMemory = [](const Instruction &I) {
- return I.mayReadOrWriteMemory();
- };
- if (std::any_of(std::next(I0->getIterator()), At0, WritesMemory))
+ BasicBlock *Pred1 = *PI++;
+ if (PI != PE) // More than two predecessors.
return false;
- if (std::any_of(std::next(I1->getIterator()), At1, WritesMemory))
+ BasicBlock *BB2 = (Pred0 == BB1) ? Pred1 : Pred0;
+ BranchInst *BI2 = dyn_cast<BranchInst>(BB2->getTerminator());
+ if (!BI2 || !BI2->isUnconditional())
return false;
- return true;
-}
-// Is it legal to place a variable in operand \c OpIdx of \c I?
-// FIXME: This should be promoted to Instruction.
-static bool canReplaceOperandWithVariable(const Instruction *I,
- unsigned OpIdx) {
- // Early exit.
- if (!isa<Constant>(I->getOperand(OpIdx)))
- return true;
-
- switch (I->getOpcode()) {
- default:
- return true;
- case Instruction::Call:
- case Instruction::Invoke:
- // FIXME: many arithmetic intrinsics have no issue taking a
- // variable, however it's hard to distingish these from
- // specials such as @llvm.frameaddress that require a constant.
- return !isa<IntrinsicInst>(I);
- case Instruction::ShuffleVector:
- // Shufflevector masks are constant.
- return OpIdx != 2;
- case Instruction::ExtractValue:
- case Instruction::InsertValue:
- // All operands apart from the first are constant.
- return OpIdx == 0;
- case Instruction::Alloca:
- return false;
- case Instruction::GetElementPtr:
- if (OpIdx == 0)
- return true;
- gep_type_iterator It = std::next(gep_type_begin(I), OpIdx - 1);
- return !It->isStructTy();
- }
-}
-
-// All blocks in Blocks unconditionally jump to a common successor. Analyze
-// the last non-terminator instruction in each block and return true if it would
-// be possible to sink them into their successor, creating one common
-// instruction instead. Set NumPHIsRequired to the number of PHI nodes that
-// would need to be created during sinking.
-static bool canSinkLastInstruction(ArrayRef<BasicBlock*> Blocks,
- unsigned &NumPHIsRequired) {
- SmallVector<Instruction*,4> Insts;
- for (auto *BB : Blocks) {
- if (BB->getTerminator() == &BB->front())
- // Block was empty.
- return false;
- Insts.push_back(BB->getTerminator()->getPrevNode());
+ // Gather the PHI nodes in BBEnd.
+ SmallDenseMap<std::pair<Value *, Value *>, PHINode *> JointValueMap;
+ Instruction *FirstNonPhiInBBEnd = nullptr;
+ for (BasicBlock::iterator I = BBEnd->begin(), E = BBEnd->end(); I != E; ++I) {
+ if (PHINode *PN = dyn_cast<PHINode>(I)) {
+ Value *BB1V = PN->getIncomingValueForBlock(BB1);
+ Value *BB2V = PN->getIncomingValueForBlock(BB2);
+ JointValueMap[std::make_pair(BB1V, BB2V)] = PN;
+ } else {
+ FirstNonPhiInBBEnd = &*I;
+ break;
+ }
}
+ if (!FirstNonPhiInBBEnd)
+ return false;
- // Prune out obviously bad instructions to move. Any non-store instruction
- // must have exactly one use, and we check later that use is by a single,
- // common PHI instruction in the successor.
- for (auto *I : Insts) {
- // These instructions may change or break semantics if moved.
- if (isa<PHINode>(I) || I->isEHPad() || isa<AllocaInst>(I) ||
- I->getType()->isTokenTy())
- return false;
- // Apart from loads and stores, we won't move anything that could
- // change memory or have sideeffects.
- if (!isa<StoreInst>(I) && !isa<LoadInst>(I) &&
- (I->mayHaveSideEffects() || I->mayHaveSideEffects()))
- return false;
- // Everything must have only one use too, apart from stores which
- // have no uses.
- if (!isa<StoreInst>(I) && !I->hasOneUse())
- return false;
- }
+ // This does very trivial matching, with limited scanning, to find identical
+ // instructions in the two blocks. We scan backward for obviously identical
+ // instructions in an identical order.
+ BasicBlock::InstListType::reverse_iterator RI1 = BB1->getInstList().rbegin(),
+ RE1 = BB1->getInstList().rend(),
+ RI2 = BB2->getInstList().rbegin(),
+ RE2 = BB2->getInstList().rend();
+ // Skip debug info.
+ while (RI1 != RE1 && isa<DbgInfoIntrinsic>(&*RI1))
+ ++RI1;
+ if (RI1 == RE1)
+ return false;
+ while (RI2 != RE2 && isa<DbgInfoIntrinsic>(&*RI2))
+ ++RI2;
+ if (RI2 == RE2)
+ return false;
+ // Skip the unconditional branches.
+ ++RI1;
+ ++RI2;
- const Instruction *I0 = Insts.front();
- for (auto *I : Insts)
- if (!I->isSameOperationAs(I0))
- return false;
+ bool Changed = false;
+ while (RI1 != RE1 && RI2 != RE2) {
+ // Skip debug info.
+ while (RI1 != RE1 && isa<DbgInfoIntrinsic>(&*RI1))
+ ++RI1;
+ if (RI1 == RE1)
+ return Changed;
+ while (RI2 != RE2 && isa<DbgInfoIntrinsic>(&*RI2))
+ ++RI2;
+ if (RI2 == RE2)
+ return Changed;
- // If this isn't a store, check the only user is a single PHI.
- if (!isa<StoreInst>(I0)) {
- auto *PNUse = dyn_cast<PHINode>(*I0->user_begin());
- if (!PNUse ||
- !all_of(Insts, [&PNUse](const Instruction *I) {
- return *I->user_begin() == PNUse;
- }))
- return false;
- }
+ Instruction *I1 = &*RI1, *I2 = &*RI2;
+ auto InstPair = std::make_pair(I1, I2);
+ // I1 and I2 should have a single use in the same PHI node, and they
+ // perform the same operation.
+ // Cannot move control-flow-involving, volatile loads, vaarg, etc.
+ if (isa<PHINode>(I1) || isa<PHINode>(I2) || isa<TerminatorInst>(I1) ||
+ isa<TerminatorInst>(I2) || I1->isEHPad() || I2->isEHPad() ||
+ isa<AllocaInst>(I1) || isa<AllocaInst>(I2) ||
+ I1->mayHaveSideEffects() || I2->mayHaveSideEffects() ||
+ I1->mayReadOrWriteMemory() || I2->mayReadOrWriteMemory() ||
+ !I1->hasOneUse() || !I2->hasOneUse() || !JointValueMap.count(InstPair))
+ return Changed;
- NumPHIsRequired = 0;
- for (unsigned OI = 0, OE = I0->getNumOperands(); OI != OE; ++OI) {
- if (I0->getOperand(OI)->getType()->isTokenTy())
- // Don't touch any operand of token type.
- return false;
- auto SameAsI0 = [&I0, OI](const Instruction *I) {
- return areValuesTriviallySame(I->getOperand(OI), I->getIterator(),
- I0->getOperand(OI), I0->getIterator());
- };
- if (!all_of(Insts, SameAsI0)) {
- if (!canReplaceOperandWithVariable(I0, OI))
- // We can't create a PHI from this GEP.
- return false;
- if ((isa<CallInst>(I0) || isa<InvokeInst>(I0)) && OI != 0)
- // Don't create indirect calls!
- // FIXME: if the call was *already* indirect, we should do this.
- return false;
- ++NumPHIsRequired;
+ // Check whether we should swap the operands of ICmpInst.
+ // TODO: Add support of communativity.
+ ICmpInst *ICmp1 = dyn_cast<ICmpInst>(I1), *ICmp2 = dyn_cast<ICmpInst>(I2);
+ bool SwapOpnds = false;
+ if (ICmp1 && ICmp2 && ICmp1->getOperand(0) != ICmp2->getOperand(0) &&
+ ICmp1->getOperand(1) != ICmp2->getOperand(1) &&
+ (ICmp1->getOperand(0) == ICmp2->getOperand(1) ||
+ ICmp1->getOperand(1) == ICmp2->getOperand(0))) {
+ ICmp2->swapOperands();
+ SwapOpnds = true;
}
- }
- return true;
-}
-
-// Assuming canSinkLastInstruction(Blocks) has returned true, sink the last
-// instruction of every block in Blocks to their common successor, commoning
-// into one instruction.
-static void sinkLastInstruction(ArrayRef<BasicBlock*> Blocks) {
- unsigned Dummy;
- (void)Dummy;
- assert(canSinkLastInstruction(Blocks, Dummy) &&
- "Must analyze before transforming!");
- auto *BBEnd = Blocks[0]->getTerminator()->getSuccessor(0);
-
- // canSinkLastInstruction returning true guarantees that every block has at
- // least one non-terminator instruction.
- SmallVector<Instruction*,4> Insts;
- for (auto *BB : Blocks)
- Insts.push_back(BB->getTerminator()->getPrevNode());
-
- // We don't need to do any checking here; canSinkLastInstruction should have
- // done it all for us.
- Instruction *I0 = Insts.front();
- SmallVector<Value*, 4> NewOperands;
- for (unsigned O = 0, E = I0->getNumOperands(); O != E; ++O) {
- // This check is different to that in canSinkLastInstruction. There, we
- // cared about the global view once simplifycfg (and instcombine) have
- // completed - it takes into account PHIs that become trivially
- // simplifiable. However here we need a more local view; if an operand
- // differs we create a PHI and rely on instcombine to clean up the very
- // small mess we may make.
- bool NeedPHI = any_of(Insts, [&I0, O](const Instruction *I) {
- return I->getOperand(O) != I0->getOperand(O);
- });
- if (!NeedPHI) {
- NewOperands.push_back(I0->getOperand(O));
- continue;
+ if (!I1->isSameOperationAs(I2)) {
+ if (SwapOpnds)
+ ICmp2->swapOperands();
+ return Changed;
}
- // Create a new PHI in the successor block and populate it.
- auto *Op = I0->getOperand(O);
- assert(!Op->getType()->isTokenTy() && "Can't PHI tokens!");
- auto *PN = PHINode::Create(Op->getType(), Insts.size(),
- Op->getName() + ".sink", &BBEnd->front());
- for (auto *I : Insts)
- PN->addIncoming(I->getOperand(O), I->getParent());
- NewOperands.push_back(PN);
- }
-
- // Arbitrarily use I0 as the new "common" instruction; remap its operands
- // and move it to the start of the successor block.
- for (unsigned O = 0, E = I0->getNumOperands(); O != E; ++O)
- I0->getOperandUse(O).set(NewOperands[O]);
- I0->moveBefore(&*BBEnd->getFirstInsertionPt());
-
- if (!isa<StoreInst>(I0)) {
- // canSinkLastInstruction checked that all instructions were used by
- // one and only one PHI node. Find that now, RAUW it to our common
- // instruction and nuke it.
- assert(I0->hasOneUse());
- auto *PN = cast<PHINode>(*I0->user_begin());
- PN->replaceAllUsesWith(I0);
- PN->eraseFromParent();
- }
-
- // Finally nuke all instructions apart from the common instruction.
- for (auto *I : Insts)
- if (I != I0)
- I->eraseFromParent();
-}
+ // The operands should be either the same or they need to be generated
+ // with a PHI node after sinking. We only handle the case where there is
+ // a single pair of different operands.
+ Value *DifferentOp1 = nullptr, *DifferentOp2 = nullptr;
+ unsigned Op1Idx = ~0U;
+ for (unsigned I = 0, E = I1->getNumOperands(); I != E; ++I) {
+ if (I1->getOperand(I) == I2->getOperand(I))
+ continue;
+ // Early exit if we have more-than one pair of different operands or if
+ // we need a PHI node to replace a constant.
+ if (Op1Idx != ~0U || isa<Constant>(I1->getOperand(I)) ||
+ isa<Constant>(I2->getOperand(I))) {
+ // If we can't sink the instructions, undo the swapping.
+ if (SwapOpnds)
+ ICmp2->swapOperands();
+ return Changed;
+ }
+ DifferentOp1 = I1->getOperand(I);
+ Op1Idx = I;
+ DifferentOp2 = I2->getOperand(I);
+ }
-/// Given an unconditional branch that goes to BBEnd,
-/// check whether BBEnd has only two predecessors and the other predecessor
-/// ends with an unconditional branch. If it is true, sink any common code
-/// in the two predecessors to BBEnd.
-static bool SinkThenElseCodeToEnd(BranchInst *BI1) {
- assert(BI1->isUnconditional());
- BasicBlock *BBEnd = BI1->getSuccessor(0);
+ DEBUG(dbgs() << "SINK common instructions " << *I1 << "\n");
+ DEBUG(dbgs() << " " << *I2 << "\n");
+
+ // We insert the pair of different operands to JointValueMap and
+ // remove (I1, I2) from JointValueMap.
+ if (Op1Idx != ~0U) {
+ auto &NewPN = JointValueMap[std::make_pair(DifferentOp1, DifferentOp2)];
+ if (!NewPN) {
+ NewPN =
+ PHINode::Create(DifferentOp1->getType(), 2,
+ DifferentOp1->getName() + ".sink", &BBEnd->front());
+ NewPN->addIncoming(DifferentOp1, BB1);
+ NewPN->addIncoming(DifferentOp2, BB2);
+ DEBUG(dbgs() << "Create PHI node " << *NewPN << "\n";);
+ }
+ // I1 should use NewPN instead of DifferentOp1.
+ I1->setOperand(Op1Idx, NewPN);
+ }
+ PHINode *OldPN = JointValueMap[InstPair];
+ JointValueMap.erase(InstPair);
+
+ // We need to update RE1 and RE2 if we are going to sink the first
+ // instruction in the basic block down.
+ bool UpdateRE1 = (I1 == &BB1->front()), UpdateRE2 = (I2 == &BB2->front());
+ // Sink the instruction.
+ BBEnd->getInstList().splice(FirstNonPhiInBBEnd->getIterator(),
+ BB1->getInstList(), I1);
+ if (!OldPN->use_empty())
+ OldPN->replaceAllUsesWith(I1);
+ OldPN->eraseFromParent();
- SmallVector<BasicBlock*,4> Blocks;
- for (auto *BB : predecessors(BBEnd))
- Blocks.push_back(BB);
- if (Blocks.size() != 2 ||
- !all_of(Blocks, [](const BasicBlock *BB) {
- auto *BI = dyn_cast<BranchInst>(BB->getTerminator());
- return BI && BI->isUnconditional();
- }))
- return false;
+ if (!I2->use_empty())
+ I2->replaceAllUsesWith(I1);
+ I1->intersectOptionalDataWith(I2);
+ // TODO: Use combineMetadata here to preserve what metadata we can
+ // (analogous to the hoisting case above).
+ I2->eraseFromParent();
- bool Changed = false;
- unsigned NumPHIsToInsert;
- while (canSinkLastInstruction(Blocks, NumPHIsToInsert) && NumPHIsToInsert <= 1) {
- sinkLastInstruction(Blocks);
+ if (UpdateRE1)
+ RE1 = BB1->getInstList().rend();
+ if (UpdateRE2)
+ RE2 = BB2->getInstList().rend();
+ FirstNonPhiInBBEnd = &*I1;
NumSinkCommons++;
Changed = true;
}
; CHECK: call
; CHECK: add
; CHECK-NOT: br
-
-define i32 @test4(i1 zeroext %flag, i32 %x, i32* %y) {
-entry:
- br i1 %flag, label %if.then, label %if.else
-
-if.then:
- %a = add i32 %x, 5
- store i32 %a, i32* %y
- br label %if.end
-
-if.else:
- %b = add i32 %x, 7
- store i32 %b, i32* %y
- br label %if.end
-
-if.end:
- ret i32 1
-}
-
-; CHECK-LABEL: test4
-; CHECK: select
-; CHECK: store
-; CHECK-NOT: store
-
-define i32 @test5(i1 zeroext %flag, i32 %x, i32* %y) {
-entry:
- br i1 %flag, label %if.then, label %if.else
-
-if.then:
- %a = add i32 %x, 5
- store volatile i32 %a, i32* %y
- br label %if.end
-
-if.else:
- %b = add i32 %x, 7
- store i32 %b, i32* %y
- br label %if.end
-
-if.end:
- ret i32 1
-}
-
-; CHECK-LABEL: test5
-; CHECK: store volatile
-; CHECK: store
-
-define i32 @test6(i1 zeroext %flag, i32 %x, i32* %y) {
-entry:
- br i1 %flag, label %if.then, label %if.else
-
-if.then:
- %a = add i32 %x, 5
- store volatile i32 %a, i32* %y
- br label %if.end
-
-if.else:
- %b = add i32 %x, 7
- store volatile i32 %b, i32* %y
- br label %if.end
-
-if.end:
- ret i32 1
-}
-
-; CHECK-LABEL: test6
-; CHECK: select
-; CHECK: store volatile
-; CHECK-NOT: store
-
-define i32 @test7(i1 zeroext %flag, i32 %x, i32* %y) {
-entry:
- br i1 %flag, label %if.then, label %if.else
-
-if.then:
- %z = load volatile i32, i32* %y
- %a = add i32 %z, 5
- store volatile i32 %a, i32* %y
- br label %if.end
-
-if.else:
- %w = load volatile i32, i32* %y
- %b = add i32 %w, 7
- store volatile i32 %b, i32* %y
- br label %if.end
-
-if.end:
- ret i32 1
-}
-
-; CHECK-LABEL: test7
-; CHECK-DAG: select
-; CHECK-DAG: load volatile
-; CHECK: store volatile
-; CHECK-NOT: load
-; CHECK-NOT: store
-
-; %z and %w are in different blocks. We shouldn't sink the add because
-; there may be intervening memory instructions.
-define i32 @test8(i1 zeroext %flag, i32 %x, i32* %y) {
-entry:
- %z = load volatile i32, i32* %y
- br i1 %flag, label %if.then, label %if.else
-
-if.then:
- %a = add i32 %z, 5
- store volatile i32 %a, i32* %y
- br label %if.end
-
-if.else:
- %w = load volatile i32, i32* %y
- %b = add i32 %w, 7
- store volatile i32 %b, i32* %y
- br label %if.end
-
-if.end:
- ret i32 1
-}
-
-; CHECK-LABEL: test8
-; CHECK: add
-; CHECK: add
-
-; The extra store in %if.then means %z and %w are not equivalent.
-define i32 @test9(i1 zeroext %flag, i32 %x, i32* %y, i32* %p) {
-entry:
- br i1 %flag, label %if.then, label %if.else
-
-if.then:
- store i32 7, i32* %p
- %z = load volatile i32, i32* %y
- store i32 6, i32* %p
- %a = add i32 %z, 5
- store volatile i32 %a, i32* %y
- br label %if.end
-
-if.else:
- %w = load volatile i32, i32* %y
- %b = add i32 %w, 7
- store volatile i32 %b, i32* %y
- br label %if.end
-
-if.end:
- ret i32 1
-}
-
-; CHECK-LABEL: test9
-; CHECK: add
-; CHECK: add
-
-%struct.anon = type { i32, i32 }
-
-; The GEP indexes a struct type so cannot have a variable last index.
-define i32 @test10(i1 zeroext %flag, i32 %x, i32* %y, %struct.anon* %s) {
-entry:
- br i1 %flag, label %if.then, label %if.else
-
-if.then:
- %dummy = add i32 %x, 5
- %gepa = getelementptr inbounds %struct.anon, %struct.anon* %s, i32 0, i32 0
- store volatile i32 %x, i32* %gepa
- br label %if.end
-
-if.else:
- %dummy1 = add i32 %x, 6
- %gepb = getelementptr inbounds %struct.anon, %struct.anon* %s, i32 0, i32 1
- store volatile i32 %x, i32* %gepb
- br label %if.end
-
-if.end:
- ret i32 1
-}
-
-; CHECK-LABEL: test10
-; CHECK: getelementptr
-; CHECK: getelementptr
-; CHECK: phi
-; CHECK: store volatile
-
-; The shufflevector's mask operand cannot be merged in a PHI.
-define i32 @test11(i1 zeroext %flag, i32 %w, <2 x i32> %x, <2 x i32> %y) {
-entry:
- br i1 %flag, label %if.then, label %if.else
-
-if.then:
- %dummy = add i32 %w, 5
- %sv1 = shufflevector <2 x i32> %x, <2 x i32> %y, <2 x i32> <i32 0, i32 1>
- br label %if.end
-
-if.else:
- %dummy1 = add i32 %w, 6
- %sv2 = shufflevector <2 x i32> %x, <2 x i32> %y, <2 x i32> <i32 1, i32 0>
- br label %if.end
-
-if.end:
- %p = phi <2 x i32> [ %sv1, %if.then ], [ %sv2, %if.else ]
- ret i32 1
-}
-
-; CHECK-LABEL: test11
-; CHECK: shufflevector
-; CHECK: shufflevector
-
-; We can't common an intrinsic!
-define i32 @test12(i1 zeroext %flag, i32 %w, i32 %x, i32 %y) {
-entry:
- br i1 %flag, label %if.then, label %if.else
-
-if.then:
- %dummy = add i32 %w, 5
- %sv1 = call i32 @llvm.ctlz.i32(i32 %x)
- br label %if.end
-
-if.else:
- %dummy1 = add i32 %w, 6
- %sv2 = call i32 @llvm.cttz.i32(i32 %x)
- br label %if.end
-
-if.end:
- %p = phi i32 [ %sv1, %if.then ], [ %sv2, %if.else ]
- ret i32 1
-}
-
-declare i32 @llvm.ctlz.i32(i32 %x) readnone
-declare i32 @llvm.cttz.i32(i32 %x) readnone
-
-; CHECK-LABEL: test12
-; CHECK: call i32 @llvm.ctlz
-; CHECK: call i32 @llvm.cttz
-