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DenseSet used to be implemented as DenseMap<Key, char>, which usually doubled the memory footprint of the map. Now we use a compressed set so the second element uses no memory at all. This required some surgery on DenseMap as all accesses to the bucket now have to go through methods; this should have no impact on the behavior of DenseMap though. The new default bucket type for DenseMap is a slightly extended std::pair as we expose it through DenseMap's iterator and don't want to break any existing users. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223588 91177308-0d34-0410-b5e6-96231b3b80d8
579 lines
22 KiB
C++
579 lines
22 KiB
C++
//=- AArch64PromoteConstant.cpp --- Promote constant to global for AArch64 -==//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the AArch64PromoteConstant pass which promotes constants
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// to global variables when this is likely to be more efficient. Currently only
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// types related to constant vector (i.e., constant vector, array of constant
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// vectors, constant structure with a constant vector field, etc.) are promoted
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// to global variables. Constant vectors are likely to be lowered in target
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// constant pool during instruction selection already; therefore, the access
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// will remain the same (memory load), but the structure types are not split
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// into different constant pool accesses for each field. A bonus side effect is
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// that created globals may be merged by the global merge pass.
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//
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// FIXME: This pass may be useful for other targets too.
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//===----------------------------------------------------------------------===//
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#include "AArch64.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/SmallSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/GlobalVariable.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/IR/InlineAsm.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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using namespace llvm;
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#define DEBUG_TYPE "aarch64-promote-const"
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// Stress testing mode - disable heuristics.
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static cl::opt<bool> Stress("aarch64-stress-promote-const", cl::Hidden,
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cl::desc("Promote all vector constants"));
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STATISTIC(NumPromoted, "Number of promoted constants");
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STATISTIC(NumPromotedUses, "Number of promoted constants uses");
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//===----------------------------------------------------------------------===//
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// AArch64PromoteConstant
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//===----------------------------------------------------------------------===//
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namespace {
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/// Promotes interesting constant into global variables.
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/// The motivating example is:
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/// static const uint16_t TableA[32] = {
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/// 41944, 40330, 38837, 37450, 36158, 34953, 33826, 32768,
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/// 31776, 30841, 29960, 29128, 28340, 27595, 26887, 26215,
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/// 25576, 24967, 24386, 23832, 23302, 22796, 22311, 21846,
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/// 21400, 20972, 20561, 20165, 19785, 19419, 19066, 18725,
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/// };
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///
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/// uint8x16x4_t LoadStatic(void) {
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/// uint8x16x4_t ret;
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/// ret.val[0] = vld1q_u16(TableA + 0);
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/// ret.val[1] = vld1q_u16(TableA + 8);
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/// ret.val[2] = vld1q_u16(TableA + 16);
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/// ret.val[3] = vld1q_u16(TableA + 24);
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/// return ret;
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/// }
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///
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/// The constants in this example are folded into the uses. Thus, 4 different
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/// constants are created.
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///
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/// As their type is vector the cheapest way to create them is to load them
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/// for the memory.
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///
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/// Therefore the final assembly final has 4 different loads. With this pass
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/// enabled, only one load is issued for the constants.
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class AArch64PromoteConstant : public ModulePass {
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public:
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static char ID;
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AArch64PromoteConstant() : ModulePass(ID) {}
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const char *getPassName() const override { return "AArch64 Promote Constant"; }
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/// Iterate over the functions and promote the interesting constants into
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/// global variables with module scope.
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bool runOnModule(Module &M) override {
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DEBUG(dbgs() << getPassName() << '\n');
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bool Changed = false;
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for (auto &MF : M) {
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Changed |= runOnFunction(MF);
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}
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return Changed;
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}
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private:
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/// Look for interesting constants used within the given function.
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/// Promote them into global variables, load these global variables within
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/// the related function, so that the number of inserted load is minimal.
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bool runOnFunction(Function &F);
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// This transformation requires dominator info
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.setPreservesCFG();
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AU.addRequired<DominatorTreeWrapperPass>();
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AU.addPreserved<DominatorTreeWrapperPass>();
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}
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/// Type to store a list of User.
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typedef SmallVector<Value::user_iterator, 4> Users;
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/// Map an insertion point to all the uses it dominates.
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typedef DenseMap<Instruction *, Users> InsertionPoints;
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/// Map a function to the required insertion point of load for a
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/// global variable.
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typedef DenseMap<Function *, InsertionPoints> InsertionPointsPerFunc;
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/// Find the closest point that dominates the given Use.
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Instruction *findInsertionPoint(Value::user_iterator &Use);
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/// Check if the given insertion point is dominated by an existing
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/// insertion point.
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/// If true, the given use is added to the list of dominated uses for
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/// the related existing point.
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/// \param NewPt the insertion point to be checked
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/// \param UseIt the use to be added into the list of dominated uses
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/// \param InsertPts existing insertion points
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/// \pre NewPt and all instruction in InsertPts belong to the same function
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/// \return true if one of the insertion point in InsertPts dominates NewPt,
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/// false otherwise
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bool isDominated(Instruction *NewPt, Value::user_iterator &UseIt,
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InsertionPoints &InsertPts);
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/// Check if the given insertion point can be merged with an existing
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/// insertion point in a common dominator.
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/// If true, the given use is added to the list of the created insertion
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/// point.
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/// \param NewPt the insertion point to be checked
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/// \param UseIt the use to be added into the list of dominated uses
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/// \param InsertPts existing insertion points
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/// \pre NewPt and all instruction in InsertPts belong to the same function
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/// \pre isDominated returns false for the exact same parameters.
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/// \return true if it exists an insertion point in InsertPts that could
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/// have been merged with NewPt in a common dominator,
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/// false otherwise
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bool tryAndMerge(Instruction *NewPt, Value::user_iterator &UseIt,
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InsertionPoints &InsertPts);
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/// Compute the minimal insertion points to dominates all the interesting
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/// uses of value.
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/// Insertion points are group per function and each insertion point
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/// contains a list of all the uses it dominates within the related function
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/// \param Val constant to be examined
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/// \param[out] InsPtsPerFunc output storage of the analysis
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void computeInsertionPoints(Constant *Val,
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InsertionPointsPerFunc &InsPtsPerFunc);
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/// Insert a definition of a new global variable at each point contained in
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/// InsPtsPerFunc and update the related uses (also contained in
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/// InsPtsPerFunc).
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bool insertDefinitions(Constant *Cst, InsertionPointsPerFunc &InsPtsPerFunc);
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/// Compute the minimal insertion points to dominate all the interesting
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/// uses of Val and insert a definition of a new global variable
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/// at these points.
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/// Also update the uses of Val accordingly.
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/// Currently a use of Val is considered interesting if:
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/// - Val is not UndefValue
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/// - Val is not zeroinitialized
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/// - Replacing Val per a load of a global variable is valid.
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/// \see shouldConvert for more details
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bool computeAndInsertDefinitions(Constant *Val);
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/// Promote the given constant into a global variable if it is expected to
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/// be profitable.
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/// \return true if Cst has been promoted
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bool promoteConstant(Constant *Cst);
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/// Transfer the list of dominated uses of IPI to NewPt in InsertPts.
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/// Append UseIt to this list and delete the entry of IPI in InsertPts.
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static void appendAndTransferDominatedUses(Instruction *NewPt,
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Value::user_iterator &UseIt,
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InsertionPoints::iterator &IPI,
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InsertionPoints &InsertPts) {
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// Record the dominated use.
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IPI->second.push_back(UseIt);
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// Transfer the dominated uses of IPI to NewPt
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// Inserting into the DenseMap may invalidate existing iterator.
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// Keep a copy of the key to find the iterator to erase.
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Instruction *OldInstr = IPI->first;
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InsertPts[NewPt] = std::move(IPI->second);
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// Erase IPI.
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IPI = InsertPts.find(OldInstr);
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InsertPts.erase(IPI);
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}
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};
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} // end anonymous namespace
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char AArch64PromoteConstant::ID = 0;
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namespace llvm {
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void initializeAArch64PromoteConstantPass(PassRegistry &);
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}
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INITIALIZE_PASS_BEGIN(AArch64PromoteConstant, "aarch64-promote-const",
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"AArch64 Promote Constant Pass", false, false)
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INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
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INITIALIZE_PASS_END(AArch64PromoteConstant, "aarch64-promote-const",
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"AArch64 Promote Constant Pass", false, false)
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ModulePass *llvm::createAArch64PromoteConstantPass() {
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return new AArch64PromoteConstant();
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}
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/// Check if the given type uses a vector type.
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static bool isConstantUsingVectorTy(const Type *CstTy) {
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if (CstTy->isVectorTy())
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return true;
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if (CstTy->isStructTy()) {
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for (unsigned EltIdx = 0, EndEltIdx = CstTy->getStructNumElements();
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EltIdx < EndEltIdx; ++EltIdx)
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if (isConstantUsingVectorTy(CstTy->getStructElementType(EltIdx)))
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return true;
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} else if (CstTy->isArrayTy())
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return isConstantUsingVectorTy(CstTy->getArrayElementType());
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return false;
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}
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/// Check if the given use (Instruction + OpIdx) of Cst should be converted into
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/// a load of a global variable initialized with Cst.
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/// A use should be converted if it is legal to do so.
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/// For instance, it is not legal to turn the mask operand of a shuffle vector
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/// into a load of a global variable.
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static bool shouldConvertUse(const Constant *Cst, const Instruction *Instr,
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unsigned OpIdx) {
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// shufflevector instruction expects a const for the mask argument, i.e., the
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// third argument. Do not promote this use in that case.
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if (isa<const ShuffleVectorInst>(Instr) && OpIdx == 2)
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return false;
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// extractvalue instruction expects a const idx.
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if (isa<const ExtractValueInst>(Instr) && OpIdx > 0)
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return false;
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// extractvalue instruction expects a const idx.
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if (isa<const InsertValueInst>(Instr) && OpIdx > 1)
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return false;
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if (isa<const AllocaInst>(Instr) && OpIdx > 0)
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return false;
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// Alignment argument must be constant.
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if (isa<const LoadInst>(Instr) && OpIdx > 0)
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return false;
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// Alignment argument must be constant.
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if (isa<const StoreInst>(Instr) && OpIdx > 1)
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return false;
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// Index must be constant.
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if (isa<const GetElementPtrInst>(Instr) && OpIdx > 0)
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return false;
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// Personality function and filters must be constant.
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// Give up on that instruction.
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if (isa<const LandingPadInst>(Instr))
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return false;
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// Switch instruction expects constants to compare to.
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if (isa<const SwitchInst>(Instr))
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return false;
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// Expected address must be a constant.
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if (isa<const IndirectBrInst>(Instr))
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return false;
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// Do not mess with intrinsics.
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if (isa<const IntrinsicInst>(Instr))
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return false;
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// Do not mess with inline asm.
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const CallInst *CI = dyn_cast<const CallInst>(Instr);
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if (CI && isa<const InlineAsm>(CI->getCalledValue()))
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return false;
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return true;
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}
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/// Check if the given Cst should be converted into
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/// a load of a global variable initialized with Cst.
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/// A constant should be converted if it is likely that the materialization of
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/// the constant will be tricky. Thus, we give up on zero or undef values.
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///
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/// \todo Currently, accept only vector related types.
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/// Also we give up on all simple vector type to keep the existing
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/// behavior. Otherwise, we should push here all the check of the lowering of
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/// BUILD_VECTOR. By giving up, we lose the potential benefit of merging
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/// constant via global merge and the fact that the same constant is stored
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/// only once with this method (versus, as many function that uses the constant
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/// for the regular approach, even for float).
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/// Again, the simplest solution would be to promote every
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/// constant and rematerialize them when they are actually cheap to create.
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static bool shouldConvert(const Constant *Cst) {
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if (isa<const UndefValue>(Cst))
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return false;
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// FIXME: In some cases, it may be interesting to promote in memory
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// a zero initialized constant.
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// E.g., when the type of Cst require more instructions than the
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// adrp/add/load sequence or when this sequence can be shared by several
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// instances of Cst.
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// Ideally, we could promote this into a global and rematerialize the constant
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// when it was a bad idea.
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if (Cst->isZeroValue())
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return false;
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if (Stress)
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return true;
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// FIXME: see function \todo
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if (Cst->getType()->isVectorTy())
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return false;
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return isConstantUsingVectorTy(Cst->getType());
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}
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Instruction *
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AArch64PromoteConstant::findInsertionPoint(Value::user_iterator &Use) {
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// If this user is a phi, the insertion point is in the related
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// incoming basic block.
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PHINode *PhiInst = dyn_cast<PHINode>(*Use);
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Instruction *InsertionPoint;
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if (PhiInst)
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InsertionPoint =
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PhiInst->getIncomingBlock(Use.getOperandNo())->getTerminator();
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else
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InsertionPoint = dyn_cast<Instruction>(*Use);
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assert(InsertionPoint && "User is not an instruction!");
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return InsertionPoint;
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}
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bool AArch64PromoteConstant::isDominated(Instruction *NewPt,
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Value::user_iterator &UseIt,
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InsertionPoints &InsertPts) {
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DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>(
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*NewPt->getParent()->getParent()).getDomTree();
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// Traverse all the existing insertion points and check if one is dominating
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// NewPt. If it is, remember that.
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for (auto &IPI : InsertPts) {
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if (NewPt == IPI.first || DT.dominates(IPI.first, NewPt) ||
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// When IPI.first is a terminator instruction, DT may think that
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// the result is defined on the edge.
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// Here we are testing the insertion point, not the definition.
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(IPI.first->getParent() != NewPt->getParent() &&
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DT.dominates(IPI.first->getParent(), NewPt->getParent()))) {
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// No need to insert this point. Just record the dominated use.
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DEBUG(dbgs() << "Insertion point dominated by:\n");
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DEBUG(IPI.first->print(dbgs()));
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DEBUG(dbgs() << '\n');
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IPI.second.push_back(UseIt);
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return true;
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}
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}
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return false;
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}
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bool AArch64PromoteConstant::tryAndMerge(Instruction *NewPt,
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Value::user_iterator &UseIt,
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InsertionPoints &InsertPts) {
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DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>(
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*NewPt->getParent()->getParent()).getDomTree();
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BasicBlock *NewBB = NewPt->getParent();
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// Traverse all the existing insertion point and check if one is dominated by
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// NewPt and thus useless or can be combined with NewPt into a common
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// dominator.
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for (InsertionPoints::iterator IPI = InsertPts.begin(),
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EndIPI = InsertPts.end();
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IPI != EndIPI; ++IPI) {
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BasicBlock *CurBB = IPI->first->getParent();
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if (NewBB == CurBB) {
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// Instructions are in the same block.
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// By construction, NewPt is dominating the other.
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// Indeed, isDominated returned false with the exact same arguments.
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DEBUG(dbgs() << "Merge insertion point with:\n");
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DEBUG(IPI->first->print(dbgs()));
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DEBUG(dbgs() << "\nat considered insertion point.\n");
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appendAndTransferDominatedUses(NewPt, UseIt, IPI, InsertPts);
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return true;
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}
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// Look for a common dominator
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BasicBlock *CommonDominator = DT.findNearestCommonDominator(NewBB, CurBB);
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// If none exists, we cannot merge these two points.
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if (!CommonDominator)
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continue;
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if (CommonDominator != NewBB) {
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// By construction, the CommonDominator cannot be CurBB.
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assert(CommonDominator != CurBB &&
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"Instruction has not been rejected during isDominated check!");
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// Take the last instruction of the CommonDominator as insertion point
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NewPt = CommonDominator->getTerminator();
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}
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// else, CommonDominator is the block of NewBB, hence NewBB is the last
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// possible insertion point in that block.
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DEBUG(dbgs() << "Merge insertion point with:\n");
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DEBUG(IPI->first->print(dbgs()));
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DEBUG(dbgs() << '\n');
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DEBUG(NewPt->print(dbgs()));
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DEBUG(dbgs() << '\n');
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appendAndTransferDominatedUses(NewPt, UseIt, IPI, InsertPts);
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return true;
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}
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return false;
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}
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void AArch64PromoteConstant::computeInsertionPoints(
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Constant *Val, InsertionPointsPerFunc &InsPtsPerFunc) {
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DEBUG(dbgs() << "** Compute insertion points **\n");
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for (Value::user_iterator UseIt = Val->user_begin(),
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EndUseIt = Val->user_end();
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UseIt != EndUseIt; ++UseIt) {
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// If the user is not an Instruction, we cannot modify it.
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if (!isa<Instruction>(*UseIt))
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continue;
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// Filter out uses that should not be converted.
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if (!shouldConvertUse(Val, cast<Instruction>(*UseIt), UseIt.getOperandNo()))
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continue;
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DEBUG(dbgs() << "Considered use, opidx " << UseIt.getOperandNo() << ":\n");
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DEBUG((*UseIt)->print(dbgs()));
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DEBUG(dbgs() << '\n');
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Instruction *InsertionPoint = findInsertionPoint(UseIt);
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DEBUG(dbgs() << "Considered insertion point:\n");
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DEBUG(InsertionPoint->print(dbgs()));
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DEBUG(dbgs() << '\n');
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// Check if the current insertion point is useless, i.e., it is dominated
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// by another one.
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InsertionPoints &InsertPts =
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InsPtsPerFunc[InsertionPoint->getParent()->getParent()];
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if (isDominated(InsertionPoint, UseIt, InsertPts))
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continue;
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// This insertion point is useful, check if we can merge some insertion
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// point in a common dominator or if NewPt dominates an existing one.
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if (tryAndMerge(InsertionPoint, UseIt, InsertPts))
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continue;
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DEBUG(dbgs() << "Keep considered insertion point\n");
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|
// It is definitely useful by its own
|
|
InsertPts[InsertionPoint].push_back(UseIt);
|
|
}
|
|
}
|
|
|
|
bool AArch64PromoteConstant::insertDefinitions(
|
|
Constant *Cst, InsertionPointsPerFunc &InsPtsPerFunc) {
|
|
// We will create one global variable per Module.
|
|
DenseMap<Module *, GlobalVariable *> ModuleToMergedGV;
|
|
bool HasChanged = false;
|
|
|
|
// Traverse all insertion points in all the function.
|
|
for (InsertionPointsPerFunc::iterator FctToInstPtsIt = InsPtsPerFunc.begin(),
|
|
EndIt = InsPtsPerFunc.end();
|
|
FctToInstPtsIt != EndIt; ++FctToInstPtsIt) {
|
|
InsertionPoints &InsertPts = FctToInstPtsIt->second;
|
|
// Do more checking for debug purposes.
|
|
#ifndef NDEBUG
|
|
DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>(
|
|
*FctToInstPtsIt->first).getDomTree();
|
|
#endif
|
|
GlobalVariable *PromotedGV;
|
|
assert(!InsertPts.empty() && "Empty uses does not need a definition");
|
|
|
|
Module *M = FctToInstPtsIt->first->getParent();
|
|
DenseMap<Module *, GlobalVariable *>::iterator MapIt =
|
|
ModuleToMergedGV.find(M);
|
|
if (MapIt == ModuleToMergedGV.end()) {
|
|
PromotedGV = new GlobalVariable(
|
|
*M, Cst->getType(), true, GlobalValue::InternalLinkage, nullptr,
|
|
"_PromotedConst", nullptr, GlobalVariable::NotThreadLocal);
|
|
PromotedGV->setInitializer(Cst);
|
|
ModuleToMergedGV[M] = PromotedGV;
|
|
DEBUG(dbgs() << "Global replacement: ");
|
|
DEBUG(PromotedGV->print(dbgs()));
|
|
DEBUG(dbgs() << '\n');
|
|
++NumPromoted;
|
|
HasChanged = true;
|
|
} else {
|
|
PromotedGV = MapIt->second;
|
|
}
|
|
|
|
for (InsertionPoints::iterator IPI = InsertPts.begin(),
|
|
EndIPI = InsertPts.end();
|
|
IPI != EndIPI; ++IPI) {
|
|
// Create the load of the global variable.
|
|
IRBuilder<> Builder(IPI->first->getParent(), IPI->first);
|
|
LoadInst *LoadedCst = Builder.CreateLoad(PromotedGV);
|
|
DEBUG(dbgs() << "**********\n");
|
|
DEBUG(dbgs() << "New def: ");
|
|
DEBUG(LoadedCst->print(dbgs()));
|
|
DEBUG(dbgs() << '\n');
|
|
|
|
// Update the dominated uses.
|
|
Users &DominatedUsers = IPI->second;
|
|
for (Value::user_iterator Use : DominatedUsers) {
|
|
#ifndef NDEBUG
|
|
assert((DT.dominates(LoadedCst, cast<Instruction>(*Use)) ||
|
|
(isa<PHINode>(*Use) &&
|
|
DT.dominates(LoadedCst, findInsertionPoint(Use)))) &&
|
|
"Inserted definition does not dominate all its uses!");
|
|
#endif
|
|
DEBUG(dbgs() << "Use to update " << Use.getOperandNo() << ":");
|
|
DEBUG(Use->print(dbgs()));
|
|
DEBUG(dbgs() << '\n');
|
|
Use->setOperand(Use.getOperandNo(), LoadedCst);
|
|
++NumPromotedUses;
|
|
}
|
|
}
|
|
}
|
|
return HasChanged;
|
|
}
|
|
|
|
bool AArch64PromoteConstant::computeAndInsertDefinitions(Constant *Val) {
|
|
InsertionPointsPerFunc InsertPtsPerFunc;
|
|
computeInsertionPoints(Val, InsertPtsPerFunc);
|
|
return insertDefinitions(Val, InsertPtsPerFunc);
|
|
}
|
|
|
|
bool AArch64PromoteConstant::promoteConstant(Constant *Cst) {
|
|
assert(Cst && "Given variable is not a valid constant.");
|
|
|
|
if (!shouldConvert(Cst))
|
|
return false;
|
|
|
|
DEBUG(dbgs() << "******************************\n");
|
|
DEBUG(dbgs() << "Candidate constant: ");
|
|
DEBUG(Cst->print(dbgs()));
|
|
DEBUG(dbgs() << '\n');
|
|
|
|
return computeAndInsertDefinitions(Cst);
|
|
}
|
|
|
|
bool AArch64PromoteConstant::runOnFunction(Function &F) {
|
|
// Look for instructions using constant vector. Promote that constant to a
|
|
// global variable. Create as few loads of this variable as possible and
|
|
// update the uses accordingly.
|
|
bool LocalChange = false;
|
|
SmallSet<Constant *, 8> AlreadyChecked;
|
|
|
|
for (auto &MBB : F) {
|
|
for (auto &MI : MBB) {
|
|
// Traverse the operand, looking for constant vectors. Replace them by a
|
|
// load of a global variable of constant vector type.
|
|
for (unsigned OpIdx = 0, EndOpIdx = MI.getNumOperands();
|
|
OpIdx != EndOpIdx; ++OpIdx) {
|
|
Constant *Cst = dyn_cast<Constant>(MI.getOperand(OpIdx));
|
|
// There is no point in promoting global values as they are already
|
|
// global. Do not promote constant expressions either, as they may
|
|
// require some code expansion.
|
|
if (Cst && !isa<GlobalValue>(Cst) && !isa<ConstantExpr>(Cst) &&
|
|
AlreadyChecked.insert(Cst).second)
|
|
LocalChange |= promoteConstant(Cst);
|
|
}
|
|
}
|
|
}
|
|
return LocalChange;
|
|
}
|