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[RS4GC] "Constant fold" the rs4gc-split-vector-values flag
This flag was part of a migration to a new means of handling vectors-of-points which was described in the llvm-dev thread "FYI: Relocating vector of pointers". The old code path has been off by default for a while without complaints, so time to cleanup. llvm-svn: 261569
This commit is contained in:
Philip Reames
parent
369e0e389f
commit
f10b87b138
@ -75,13 +75,6 @@ static cl::opt<bool>
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AllowStatepointWithNoDeoptInfo("rs4gc-allow-statepoint-with-no-deopt-info",
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cl::Hidden, cl::init(true));
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/// Should we split vectors of pointers into their individual elements? This
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/// is known to be buggy, but the alternate implementation isn't yet ready.
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/// This is purely to provide a debugging and dianostic hook until the vector
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/// split is replaced with vector relocations.
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static cl::opt<bool> UseVectorSplit("rs4gc-split-vector-values", cl::Hidden,
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cl::init(false));
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namespace {
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struct RewriteStatepointsForGC : public ModulePass {
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static char ID; // Pass identification, replacement for typeid
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@ -1819,139 +1812,6 @@ static void findLiveReferences(
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}
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}
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/// Remove any vector of pointers from the live set by scalarizing them over the
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/// statepoint instruction. Adds the scalarized pieces to the live set. It
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/// would be preferable to include the vector in the statepoint itself, but
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/// the lowering code currently does not handle that. Extending it would be
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/// slightly non-trivial since it requires a format change. Given how rare
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/// such cases are (for the moment?) scalarizing is an acceptable compromise.
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static void splitVectorValues(Instruction *StatepointInst,
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StatepointLiveSetTy &LiveSet,
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DenseMap<Value *, Value *>& PointerToBase,
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DominatorTree &DT) {
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SmallVector<Value *, 16> ToSplit;
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for (Value *V : LiveSet)
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if (isa<VectorType>(V->getType()))
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ToSplit.push_back(V);
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if (ToSplit.empty())
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return;
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DenseMap<Value *, SmallVector<Value *, 16>> ElementMapping;
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Function &F = *(StatepointInst->getParent()->getParent());
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DenseMap<Value *, AllocaInst *> AllocaMap;
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// First is normal return, second is exceptional return (invoke only)
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DenseMap<Value *, std::pair<Value *, Value *>> Replacements;
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for (Value *V : ToSplit) {
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AllocaInst *Alloca =
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new AllocaInst(V->getType(), "", F.getEntryBlock().getFirstNonPHI());
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AllocaMap[V] = Alloca;
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VectorType *VT = cast<VectorType>(V->getType());
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IRBuilder<> Builder(StatepointInst);
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SmallVector<Value *, 16> Elements;
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for (unsigned i = 0; i < VT->getNumElements(); i++)
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Elements.push_back(Builder.CreateExtractElement(V, Builder.getInt32(i)));
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ElementMapping[V] = Elements;
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auto InsertVectorReform = [&](Instruction *IP) {
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Builder.SetInsertPoint(IP);
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Builder.SetCurrentDebugLocation(IP->getDebugLoc());
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Value *ResultVec = UndefValue::get(VT);
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for (unsigned i = 0; i < VT->getNumElements(); i++)
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ResultVec = Builder.CreateInsertElement(ResultVec, Elements[i],
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Builder.getInt32(i));
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return ResultVec;
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};
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if (isa<CallInst>(StatepointInst)) {
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BasicBlock::iterator Next(StatepointInst);
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Next++;
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Instruction *IP = &*(Next);
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Replacements[V].first = InsertVectorReform(IP);
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Replacements[V].second = nullptr;
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} else {
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InvokeInst *Invoke = cast<InvokeInst>(StatepointInst);
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// We've already normalized - check that we don't have shared destination
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// blocks
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BasicBlock *NormalDest = Invoke->getNormalDest();
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assert(!isa<PHINode>(NormalDest->begin()));
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BasicBlock *UnwindDest = Invoke->getUnwindDest();
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assert(!isa<PHINode>(UnwindDest->begin()));
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// Insert insert element sequences in both successors
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Instruction *IP = &*(NormalDest->getFirstInsertionPt());
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Replacements[V].first = InsertVectorReform(IP);
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IP = &*(UnwindDest->getFirstInsertionPt());
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Replacements[V].second = InsertVectorReform(IP);
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}
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}
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for (Value *V : ToSplit) {
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AllocaInst *Alloca = AllocaMap[V];
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// Capture all users before we start mutating use lists
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SmallVector<Instruction *, 16> Users;
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for (User *U : V->users())
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Users.push_back(cast<Instruction>(U));
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for (Instruction *I : Users) {
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if (auto Phi = dyn_cast<PHINode>(I)) {
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for (unsigned i = 0; i < Phi->getNumIncomingValues(); i++)
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if (V == Phi->getIncomingValue(i)) {
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LoadInst *Load = new LoadInst(
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Alloca, "", Phi->getIncomingBlock(i)->getTerminator());
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Phi->setIncomingValue(i, Load);
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}
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} else {
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LoadInst *Load = new LoadInst(Alloca, "", I);
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I->replaceUsesOfWith(V, Load);
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}
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}
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// Store the original value and the replacement value into the alloca
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StoreInst *Store = new StoreInst(V, Alloca);
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if (auto I = dyn_cast<Instruction>(V))
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Store->insertAfter(I);
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else
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Store->insertAfter(Alloca);
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// Normal return for invoke, or call return
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Instruction *Replacement = cast<Instruction>(Replacements[V].first);
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(new StoreInst(Replacement, Alloca))->insertAfter(Replacement);
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// Unwind return for invoke only
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Replacement = cast_or_null<Instruction>(Replacements[V].second);
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if (Replacement)
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(new StoreInst(Replacement, Alloca))->insertAfter(Replacement);
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}
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// apply mem2reg to promote alloca to SSA
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SmallVector<AllocaInst *, 16> Allocas;
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for (Value *V : ToSplit)
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Allocas.push_back(AllocaMap[V]);
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PromoteMemToReg(Allocas, DT);
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// Update our tracking of live pointers and base mappings to account for the
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// changes we just made.
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for (Value *V : ToSplit) {
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auto &Elements = ElementMapping[V];
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LiveSet.erase(V);
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LiveSet.insert(Elements.begin(), Elements.end());
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// We need to update the base mapping as well.
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assert(PointerToBase.count(V));
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Value *OldBase = PointerToBase[V];
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auto &BaseElements = ElementMapping[OldBase];
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PointerToBase.erase(V);
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assert(Elements.size() == BaseElements.size());
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for (unsigned i = 0; i < Elements.size(); i++) {
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Value *Elem = Elements[i];
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PointerToBase[Elem] = BaseElements[i];
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}
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}
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}
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// Helper function for the "rematerializeLiveValues". It walks use chain
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// starting from the "CurrentValue" until it meets "BaseValue". Only "simple"
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// values are visited (currently it is GEP's and casts). Returns true if it
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@ -2268,22 +2128,6 @@ static bool insertParsePoints(Function &F, DominatorTree &DT,
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Holders.clear();
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// Do a limited scalarization of any live at safepoint vector values which
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// contain pointers. This enables this pass to run after vectorization at
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// the cost of some possible performance loss. Note: This is known to not
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// handle updating of the side tables correctly which can lead to relocation
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// bugs when the same vector is live at multiple statepoints. We're in the
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// process of implementing the alternate lowering - relocating the
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// vector-of-pointers as first class item and updating the backend to
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// understand that - but that's not yet complete.
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if (UseVectorSplit)
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for (size_t i = 0; i < Records.size(); i++) {
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PartiallyConstructedSafepointRecord &Info = Records[i];
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Instruction *Statepoint = ToUpdate[i].getInstruction();
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splitVectorValues(cast<Instruction>(Statepoint), Info.LiveSet,
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Info.PointerToBase, DT);
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}
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// In order to reduce live set of statepoint we might choose to rematerialize
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// some values instead of relocating them. This is purely an optimization and
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// does not influence correctness.
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@ -1,6 +1,6 @@
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; Test that we can correctly handle vectors of pointers in statepoint
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; rewriting.
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; RUN: opt < %s -rewrite-statepoints-for-gc -rs4gc-split-vector-values=0 -S | FileCheck %s
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; RUN: opt < %s -rewrite-statepoints-for-gc -S | FileCheck %s
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; A non-vector relocation for comparison
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define i64 addrspace(1)* @test(i64 addrspace(1)* %obj) gc "statepoint-example" {
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@ -1,167 +0,0 @@
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; Test that we can correctly handle vectors of pointers in statepoint
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; rewriting. Currently, we scalarize, but that's an implementation detail.
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; RUN: opt < %s -rewrite-statepoints-for-gc -rs4gc-split-vector-values -S | FileCheck %s
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; A non-vector relocation for comparison
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define i64 addrspace(1)* @test(i64 addrspace(1)* %obj) gc "statepoint-example" {
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; CHECK-LABEL: test
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; CHECK: gc.statepoint
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; CHECK-NEXT: gc.relocate
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; CHECK-NEXT: bitcast
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; CHECK-NEXT: ret i64 addrspace(1)* %obj.relocated.casted
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; A base vector from a argument
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entry:
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call void @do_safepoint() [ "deopt"() ]
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ret i64 addrspace(1)* %obj
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}
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define <2 x i64 addrspace(1)*> @test2(<2 x i64 addrspace(1)*> %obj) gc "statepoint-example" {
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; CHECK-LABEL: test2
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; CHECK: extractelement
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; CHECK-NEXT: extractelement
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; CHECK-NEXT: gc.statepoint
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; CHECK-NEXT: gc.relocate
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; CHECK-NEXT: bitcast
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; CHECK-NEXT: gc.relocate
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; CHECK-NEXT: bitcast
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; CHECK-NEXT: insertelement
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; CHECK-NEXT: insertelement
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; CHECK-NEXT: ret <2 x i64 addrspace(1)*> %7
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; A base vector from a load
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entry:
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call void @do_safepoint() [ "deopt"() ]
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ret <2 x i64 addrspace(1)*> %obj
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}
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define <2 x i64 addrspace(1)*> @test3(<2 x i64 addrspace(1)*>* %ptr) gc "statepoint-example" {
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; CHECK-LABEL: test3
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; CHECK: load
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; CHECK-NEXT: extractelement
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; CHECK-NEXT: extractelement
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; CHECK-NEXT: gc.statepoint
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; CHECK-NEXT: gc.relocate
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; CHECK-NEXT: bitcast
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; CHECK-NEXT: gc.relocate
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; CHECK-NEXT: bitcast
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; CHECK-NEXT: insertelement
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; CHECK-NEXT: insertelement
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; CHECK-NEXT: ret <2 x i64 addrspace(1)*> %7
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; When a statepoint is an invoke rather than a call
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entry:
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%obj = load <2 x i64 addrspace(1)*>, <2 x i64 addrspace(1)*>* %ptr
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call void @do_safepoint() [ "deopt"() ]
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ret <2 x i64 addrspace(1)*> %obj
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}
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declare i32 @fake_personality_function()
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define <2 x i64 addrspace(1)*> @test4(<2 x i64 addrspace(1)*>* %ptr) gc "statepoint-example" personality i32 ()* @fake_personality_function {
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; CHECK-LABEL: test4
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; CHECK: load
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; CHECK-NEXT: extractelement
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; CHECK-NEXT: extractelement
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; CHECK-NEXT: gc.statepoint
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entry:
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%obj = load <2 x i64 addrspace(1)*>, <2 x i64 addrspace(1)*>* %ptr
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invoke void @do_safepoint() [ "deopt"() ]
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to label %normal_return unwind label %exceptional_return
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normal_return: ; preds = %entry
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; CHECK-LABEL: normal_return:
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; CHECK: gc.relocate
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; CHECK-NEXT: bitcast
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; CHECK-NEXT: gc.relocate
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; CHECK-NEXT: bitcast
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; CHECK-NEXT: insertelement
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; CHECK-NEXT: insertelement
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; CHECK-NEXT: ret <2 x i64 addrspace(1)*> %7
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ret <2 x i64 addrspace(1)*> %obj
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exceptional_return: ; preds = %entry
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; CHECK-LABEL: exceptional_return:
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; CHECK: gc.relocate
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; CHECK-NEXT: bitcast
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; CHECK-NEXT: gc.relocate
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; CHECK-NEXT: bitcast
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; CHECK-NEXT: insertelement
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; CHECK-NEXT: insertelement
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; CHECK-NEXT: ret <2 x i64 addrspace(1)*> %13
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; Can we handle an insert element with a constant offset? This effectively
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; tests both the equal and inequal case since we have to relocate both indices
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; in the vector.
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%landing_pad4 = landingpad token
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cleanup
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ret <2 x i64 addrspace(1)*> %obj
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}
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define <2 x i64 addrspace(1)*> @test5(i64 addrspace(1)* %p) gc "statepoint-example" {
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; CHECK-LABEL: test5
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; CHECK: insertelement
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; CHECK-NEXT: insertelement
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; CHECK-NEXT: extractelement
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; CHECK-NEXT: extractelement
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; CHECK-NEXT: extractelement
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; CHECK-NEXT: extractelement
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; CHECK-NEXT: gc.statepoint
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; CHECK-NEXT: gc.relocate
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; CHECK-NEXT: bitcast
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; CHECK-NEXT: gc.relocate
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; CHECK-NEXT: bitcast
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; CHECK-NEXT: gc.relocate
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; CHECK-NEXT: bitcast
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; CHECK-NEXT: gc.relocate
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; CHECK-NEXT: bitcast
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; CHECK-NEXT: insertelement
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; CHECK-NEXT: insertelement
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; CHECK-NEXT: insertelement
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; CHECK-NEXT: insertelement
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; CHECK-NEXT: ret <2 x i64 addrspace(1)*>
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; A base vector from a load
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entry:
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%vec = insertelement <2 x i64 addrspace(1)*> undef, i64 addrspace(1)* %p, i32 0
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call void @do_safepoint() [ "deopt"() ]
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ret <2 x i64 addrspace(1)*> %vec
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}
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define <2 x i64 addrspace(1)*> @test6(i1 %cnd, <2 x i64 addrspace(1)*>* %ptr) gc "statepoint-example" {
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; CHECK-LABEL: test6
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entry:
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br i1 %cnd, label %taken, label %untaken
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taken: ; preds = %entry
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%obja = load <2 x i64 addrspace(1)*>, <2 x i64 addrspace(1)*>* %ptr
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br label %merge
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untaken: ; preds = %entry
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%objb = load <2 x i64 addrspace(1)*>, <2 x i64 addrspace(1)*>* %ptr
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br label %merge
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merge: ; preds = %untaken, %taken
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; CHECK-LABEL: merge:
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; CHECK-NEXT: = phi
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; CHECK-NEXT: = phi
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; CHECK-NEXT: extractelement
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; CHECK-NEXT: extractelement
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; CHECK-NEXT: extractelement
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; CHECK-NEXT: extractelement
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; CHECK-NEXT: gc.statepoint
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; CHECK-NEXT: gc.relocate
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; CHECK-NEXT: bitcast
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; CHECK-NEXT: gc.relocate
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; CHECK-NEXT: bitcast
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; CHECK-NEXT: gc.relocate
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; CHECK-NEXT: bitcast
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; CHECK-NEXT: gc.relocate
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; CHECK-NEXT: bitcast
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; CHECK-NEXT: insertelement
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; CHECK-NEXT: insertelement
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; CHECK-NEXT: insertelement
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; CHECK-NEXT: insertelement
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; CHECK-NEXT: ret <2 x i64 addrspace(1)*>
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%obj = phi <2 x i64 addrspace(1)*> [ %obja, %taken ], [ %objb, %untaken ]
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call void @do_safepoint() [ "deopt"() ]
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ret <2 x i64 addrspace(1)*> %obj
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}
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declare void @do_safepoint()
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