llvm/lib/Target/AArch64/SMEABIPass.cpp

   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 }