+// Computes a map of base pointer relocation instructions to corresponding
+// derived pointer relocation instructions given a vector of all relocate calls
+static void computeBaseDerivedRelocateMap(
+ const SmallVectorImpl<User *> &AllRelocateCalls,
+ DenseMap<IntrinsicInst *, SmallVector<IntrinsicInst *, 2>> &
+ RelocateInstMap) {
+ // Collect information in two maps: one primarily for locating the base object
+ // while filling the second map; the second map is the final structure holding
+ // a mapping between Base and corresponding Derived relocate calls
+ DenseMap<std::pair<unsigned, unsigned>, IntrinsicInst *> RelocateIdxMap;
+ for (auto &U : AllRelocateCalls) {
+ GCRelocateOperands ThisRelocate(U);
+ IntrinsicInst *I = cast<IntrinsicInst>(U);
+ auto K = std::make_pair(ThisRelocate.getBasePtrIndex(),
+ ThisRelocate.getDerivedPtrIndex());
+ RelocateIdxMap.insert(std::make_pair(K, I));
+ }
+ for (auto &Item : RelocateIdxMap) {
+ std::pair<unsigned, unsigned> Key = Item.first;
+ if (Key.first == Key.second)
+ // Base relocation: nothing to insert
+ continue;
+
+ IntrinsicInst *I = Item.second;
+ auto BaseKey = std::make_pair(Key.first, Key.first);
+
+ // We're iterating over RelocateIdxMap so we cannot modify it.
+ auto MaybeBase = RelocateIdxMap.find(BaseKey);
+ if (MaybeBase == RelocateIdxMap.end())
+ // TODO: We might want to insert a new base object relocate and gep off
+ // that, if there are enough derived object relocates.
+ continue;
+
+ RelocateInstMap[MaybeBase->second].push_back(I);
+ }
+}
+
+// Accepts a GEP and extracts the operands into a vector provided they're all
+// small integer constants
+static bool getGEPSmallConstantIntOffsetV(GetElementPtrInst *GEP,
+ SmallVectorImpl<Value *> &OffsetV) {
+ for (unsigned i = 1; i < GEP->getNumOperands(); i++) {
+ // Only accept small constant integer operands
+ auto Op = dyn_cast<ConstantInt>(GEP->getOperand(i));
+ if (!Op || Op->getZExtValue() > 20)
+ return false;
+ }
+
+ for (unsigned i = 1; i < GEP->getNumOperands(); i++)
+ OffsetV.push_back(GEP->getOperand(i));
+ return true;
+}
+
+// Takes a RelocatedBase (base pointer relocation instruction) and Targets to
+// replace, computes a replacement, and affects it.
+static bool
+simplifyRelocatesOffABase(IntrinsicInst *RelocatedBase,
+ const SmallVectorImpl<IntrinsicInst *> &Targets) {
+ bool MadeChange = false;
+ for (auto &ToReplace : Targets) {
+ GCRelocateOperands MasterRelocate(RelocatedBase);
+ GCRelocateOperands ThisRelocate(ToReplace);
+
+ assert(ThisRelocate.getBasePtrIndex() == MasterRelocate.getBasePtrIndex() &&
+ "Not relocating a derived object of the original base object");
+ if (ThisRelocate.getBasePtrIndex() == ThisRelocate.getDerivedPtrIndex()) {
+ // A duplicate relocate call. TODO: coalesce duplicates.
+ continue;
+ }
+
+ Value *Base = ThisRelocate.getBasePtr();
+ auto Derived = dyn_cast<GetElementPtrInst>(ThisRelocate.getDerivedPtr());
+ if (!Derived || Derived->getPointerOperand() != Base)
+ continue;
+
+ SmallVector<Value *, 2> OffsetV;
+ if (!getGEPSmallConstantIntOffsetV(Derived, OffsetV))
+ continue;
+
+ // Create a Builder and replace the target callsite with a gep
+ assert(RelocatedBase->getNextNode() && "Should always have one since it's not a terminator");
+
+ // Insert after RelocatedBase
+ IRBuilder<> Builder(RelocatedBase->getNextNode());
+ Builder.SetCurrentDebugLocation(ToReplace->getDebugLoc());
+
+ // If gc_relocate does not match the actual type, cast it to the right type.
+ // In theory, there must be a bitcast after gc_relocate if the type does not
+ // match, and we should reuse it to get the derived pointer. But it could be
+ // cases like this:
+ // bb1:
+ // ...
+ // %g1 = call coldcc i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(...)
+ // br label %merge
+ //
+ // bb2:
+ // ...
+ // %g2 = call coldcc i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(...)
+ // br label %merge
+ //
+ // merge:
+ // %p1 = phi i8 addrspace(1)* [ %g1, %bb1 ], [ %g2, %bb2 ]
+ // %cast = bitcast i8 addrspace(1)* %p1 in to i32 addrspace(1)*
+ //
+ // In this case, we can not find the bitcast any more. So we insert a new bitcast
+ // no matter there is already one or not. In this way, we can handle all cases, and
+ // the extra bitcast should be optimized away in later passes.
+ Instruction *ActualRelocatedBase = RelocatedBase;
+ if (RelocatedBase->getType() != Base->getType()) {
+ ActualRelocatedBase =
+ cast<Instruction>(Builder.CreateBitCast(RelocatedBase, Base->getType()));
+ }
+ Value *Replacement = Builder.CreateGEP(
+ Derived->getSourceElementType(), ActualRelocatedBase, makeArrayRef(OffsetV));
+ Instruction *ReplacementInst = cast<Instruction>(Replacement);
+ Replacement->takeName(ToReplace);
+ // If the newly generated derived pointer's type does not match the original derived
+ // pointer's type, cast the new derived pointer to match it. Same reasoning as above.
+ Instruction *ActualReplacement = ReplacementInst;
+ if (ReplacementInst->getType() != ToReplace->getType()) {
+ ActualReplacement =
+ cast<Instruction>(Builder.CreateBitCast(ReplacementInst, ToReplace->getType()));
+ }
+ ToReplace->replaceAllUsesWith(ActualReplacement);
+ ToReplace->eraseFromParent();
+
+ MadeChange = true;
+ }
+ return MadeChange;
+}
+
+// Turns this:
+//
+// %base = ...
+// %ptr = gep %base + 15
+// %tok = statepoint (%fun, i32 0, i32 0, i32 0, %base, %ptr)
+// %base' = relocate(%tok, i32 4, i32 4)
+// %ptr' = relocate(%tok, i32 4, i32 5)
+// %val = load %ptr'
+//
+// into this:
+//
+// %base = ...
+// %ptr = gep %base + 15
+// %tok = statepoint (%fun, i32 0, i32 0, i32 0, %base, %ptr)
+// %base' = gc.relocate(%tok, i32 4, i32 4)
+// %ptr' = gep %base' + 15
+// %val = load %ptr'
+bool CodeGenPrepare::simplifyOffsetableRelocate(Instruction &I) {
+ bool MadeChange = false;
+ SmallVector<User *, 2> AllRelocateCalls;
+
+ for (auto *U : I.users())
+ if (isGCRelocate(dyn_cast<Instruction>(U)))
+ // Collect all the relocate calls associated with a statepoint
+ AllRelocateCalls.push_back(U);
+
+ // We need atleast one base pointer relocation + one derived pointer
+ // relocation to mangle
+ if (AllRelocateCalls.size() < 2)
+ return false;
+
+ // RelocateInstMap is a mapping from the base relocate instruction to the
+ // corresponding derived relocate instructions
+ DenseMap<IntrinsicInst *, SmallVector<IntrinsicInst *, 2>> RelocateInstMap;
+ computeBaseDerivedRelocateMap(AllRelocateCalls, RelocateInstMap);
+ if (RelocateInstMap.empty())
+ return false;
+
+ for (auto &Item : RelocateInstMap)
+ // Item.first is the RelocatedBase to offset against
+ // Item.second is the vector of Targets to replace
+ MadeChange = simplifyRelocatesOffABase(Item.first, Item.second);
+ return MadeChange;
+}
+