1 //===--------- SMEABI - SME ABI-------------------------------------------===// 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 // This pass implements parts of the the SME ABI, such as: 10 // * Using the lazy-save mechanism before enabling the use of ZA. 11 // * Setting up the lazy-save mechanism around invokes. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #include "AArch64.h" 16 #include "Utils/AArch64SMEAttributes.h" 17 #include "llvm/ADT/StringRef.h" 18 #include "llvm/IR/IRBuilder.h" 19 #include "llvm/IR/Instructions.h" 20 #include "llvm/IR/IntrinsicsAArch64.h" 21 #include "llvm/IR/LLVMContext.h" 22 #include "llvm/IR/Module.h" 23 #include "llvm/InitializePasses.h" 24 #include "llvm/Transforms/Utils/Cloning.h" 25 26 using namespace llvm; 27 28 #define DEBUG_TYPE "aarch64-sme-abi" 29 30 namespace { 31 struct SMEABI : public FunctionPass { 32 static char ID; // Pass identification, replacement for typeid 33 SMEABI() : FunctionPass(ID) { 34 initializeSMEABIPass(*PassRegistry::getPassRegistry()); 35 } 36 37 bool runOnFunction(Function &F) override; 38 39 private: 40 bool updateNewStateFunctions(Module *M, Function *F, IRBuilder<> &Builder, 41 SMEAttrs FnAttrs); 42 }; 43 } // end anonymous namespace 44 45 char SMEABI::ID = 0; 46 static const char *name = "SME ABI Pass"; 47 INITIALIZE_PASS_BEGIN(SMEABI, DEBUG_TYPE, name, false, false) 48 INITIALIZE_PASS_END(SMEABI, DEBUG_TYPE, name, false, false) 49 50 FunctionPass *llvm::createSMEABIPass() { return new SMEABI(); } 51 52 //===----------------------------------------------------------------------===// 53 // Utility functions 54 //===----------------------------------------------------------------------===// 55 56 // Utility function to emit a call to __arm_tpidr2_save and clear TPIDR2_EL0. 57 void emitTPIDR2Save(Module *M, IRBuilder<> &Builder) { 58 auto *TPIDR2SaveTy = 59 FunctionType::get(Builder.getVoidTy(), {}, /*IsVarArgs=*/false); 60 auto Attrs = AttributeList().addFnAttribute(M->getContext(), 61 "aarch64_pstate_sm_compatible"); 62 FunctionCallee Callee = 63 M->getOrInsertFunction("__arm_tpidr2_save", TPIDR2SaveTy, Attrs); 64 CallInst *Call = Builder.CreateCall(Callee); 65 Call->setCallingConv( 66 CallingConv::AArch64_SME_ABI_Support_Routines_PreserveMost_From_X0); 67 68 // A save to TPIDR2 should be followed by clearing TPIDR2_EL0. 69 Function *WriteIntr = 70 Intrinsic::getOrInsertDeclaration(M, Intrinsic::aarch64_sme_set_tpidr2); 71 Builder.CreateCall(WriteIntr->getFunctionType(), WriteIntr, 72 Builder.getInt64(0)); 73 } 74 75 /// This function generates code at the beginning and end of a function marked 76 /// with either `aarch64_new_za` or `aarch64_new_zt0`. 77 /// At the beginning of the function, the following code is generated: 78 /// - Commit lazy-save if active [Private-ZA Interface*] 79 /// - Enable PSTATE.ZA [Private-ZA Interface] 80 /// - Zero ZA [Has New ZA State] 81 /// - Zero ZT0 [Has New ZT0 State] 82 /// 83 /// * A function with new ZT0 state will not change ZA, so committing the 84 /// lazy-save is not strictly necessary. However, the lazy-save mechanism 85 /// may be active on entry to the function, with PSTATE.ZA set to 1. If 86 /// the new ZT0 function calls a function that does not share ZT0, we will 87 /// need to conditionally SMSTOP ZA before the call, setting PSTATE.ZA to 0. 88 /// For this reason, it's easier to always commit the lazy-save at the 89 /// beginning of the function regardless of whether it has ZA state. 90 /// 91 /// At the end of the function, PSTATE.ZA is disabled if the function has a 92 /// Private-ZA Interface. A function is considered to have a Private-ZA 93 /// interface if it does not share ZA or ZT0. 94 /// 95 bool SMEABI::updateNewStateFunctions(Module *M, Function *F, 96 IRBuilder<> &Builder, SMEAttrs FnAttrs) { 97 LLVMContext &Context = F->getContext(); 98 BasicBlock *OrigBB = &F->getEntryBlock(); 99 Builder.SetInsertPoint(&OrigBB->front()); 100 101 // Commit any active lazy-saves if this is a Private-ZA function. If the 102 // value read from TPIDR2_EL0 is not null on entry to the function then 103 // the lazy-saving scheme is active and we should call __arm_tpidr2_save 104 // to commit the lazy save. 105 if (FnAttrs.hasPrivateZAInterface()) { 106 // Create the new blocks for reading TPIDR2_EL0 & enabling ZA state. 107 auto *SaveBB = OrigBB->splitBasicBlock(OrigBB->begin(), "save.za", true); 108 auto *PreludeBB = BasicBlock::Create(Context, "prelude", F, SaveBB); 109 110 // Read TPIDR2_EL0 in PreludeBB & branch to SaveBB if not 0. 111 Builder.SetInsertPoint(PreludeBB); 112 Function *TPIDR2Intr = 113 Intrinsic::getOrInsertDeclaration(M, Intrinsic::aarch64_sme_get_tpidr2); 114 auto *TPIDR2 = Builder.CreateCall(TPIDR2Intr->getFunctionType(), TPIDR2Intr, 115 {}, "tpidr2"); 116 auto *Cmp = Builder.CreateCmp(ICmpInst::ICMP_NE, TPIDR2, 117 Builder.getInt64(0), "cmp"); 118 Builder.CreateCondBr(Cmp, SaveBB, OrigBB); 119 120 // Create a call __arm_tpidr2_save, which commits the lazy save. 121 Builder.SetInsertPoint(&SaveBB->back()); 122 emitTPIDR2Save(M, Builder); 123 124 // Enable pstate.za at the start of the function. 125 Builder.SetInsertPoint(&OrigBB->front()); 126 Function *EnableZAIntr = 127 Intrinsic::getOrInsertDeclaration(M, Intrinsic::aarch64_sme_za_enable); 128 Builder.CreateCall(EnableZAIntr->getFunctionType(), EnableZAIntr); 129 } 130 131 if (FnAttrs.isNewZA()) { 132 Function *ZeroIntr = 133 Intrinsic::getOrInsertDeclaration(M, Intrinsic::aarch64_sme_zero); 134 Builder.CreateCall(ZeroIntr->getFunctionType(), ZeroIntr, 135 Builder.getInt32(0xff)); 136 } 137 138 if (FnAttrs.isNewZT0()) { 139 Function *ClearZT0Intr = 140 Intrinsic::getOrInsertDeclaration(M, Intrinsic::aarch64_sme_zero_zt); 141 Builder.CreateCall(ClearZT0Intr->getFunctionType(), ClearZT0Intr, 142 {Builder.getInt32(0)}); 143 } 144 145 if (FnAttrs.hasPrivateZAInterface()) { 146 // Before returning, disable pstate.za 147 for (BasicBlock &BB : *F) { 148 Instruction *T = BB.getTerminator(); 149 if (!T || !isa<ReturnInst>(T)) 150 continue; 151 Builder.SetInsertPoint(T); 152 Function *DisableZAIntr = Intrinsic::getOrInsertDeclaration( 153 M, Intrinsic::aarch64_sme_za_disable); 154 Builder.CreateCall(DisableZAIntr->getFunctionType(), DisableZAIntr); 155 } 156 } 157 158 F->addFnAttr("aarch64_expanded_pstate_za"); 159 return true; 160 } 161 162 bool SMEABI::runOnFunction(Function &F) { 163 Module *M = F.getParent(); 164 LLVMContext &Context = F.getContext(); 165 IRBuilder<> Builder(Context); 166 167 if (F.isDeclaration() || F.hasFnAttribute("aarch64_expanded_pstate_za")) 168 return false; 169 170 bool Changed = false; 171 SMEAttrs FnAttrs(F); 172 if (FnAttrs.isNewZA() || FnAttrs.isNewZT0()) 173 Changed |= updateNewStateFunctions(M, &F, Builder, FnAttrs); 174 175 return Changed; 176 } 177