DeadArgumentElimination.cpp | Explore in Territory

//===- DeadArgumentElimination.cpp - Eliminate dead arguments -------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This pass deletes dead arguments from internal functions.  Dead argument
// elimination removes arguments which are directly dead, as well as arguments
// only passed into function calls as dead arguments of other functions.  This
// pass also deletes dead return values in a similar way.
//
// This pass is often useful as a cleanup pass to run after aggressive
// interprocedural passes, which add possibly-dead arguments or return values.
//
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/IPO/DeadArgumentElimination.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
#include "llvm/IR/Argument.h"
#include "llvm/IR/AttributeMask.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DIBuilder.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/NoFolder.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Use.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/IPO.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include <cassert>
#include <utility>
#include <vector>

usingnamespacellvm;

#define DEBUG_TYPE …

STATISTIC(NumArgumentsEliminated, "Number of unread args removed");
STATISTIC(NumRetValsEliminated, "Number of unused return values removed");
STATISTIC(NumArgumentsReplacedWithPoison,
          "Number of unread args replaced with poison");

namespace {

/// The dead argument elimination pass.
class DAE : public ModulePass { … };

bool isMustTailCalleeAnalyzable(const CallBase &CB) { … }

} // end anonymous namespace

char DAE::ID = …;

INITIALIZE_PASS(…)

namespace {

/// The DeadArgumentHacking pass, same as dead argument elimination, but deletes
/// arguments to functions which are external. This is only for use by bugpoint.
struct DAH : public DAE { … };

} // end anonymous namespace

char DAH::ID = …;

INITIALIZE_PASS(…)

/// This pass removes arguments from functions which are not used by the body of
/// the function.
ModulePass *llvm::createDeadArgEliminationPass() { … }

ModulePass *llvm::createDeadArgHackingPass() { … }

/// If this is an function that takes a ... list, and if llvm.vastart is never
/// called, the varargs list is dead for the function.
bool DeadArgumentEliminationPass::deleteDeadVarargs(Function &F) { … }

/// Checks if the given function has any arguments that are unused, and changes
/// the caller parameters to be poison instead.
bool DeadArgumentEliminationPass::removeDeadArgumentsFromCallers(Function &F) { … }

/// Convenience function that returns the number of return values. It returns 0
/// for void functions and 1 for functions not returning a struct. It returns
/// the number of struct elements for functions returning a struct.
static unsigned numRetVals(const Function *F) { … }

/// Returns the sub-type a function will return at a given Idx. Should
/// correspond to the result type of an ExtractValue instruction executed with
/// just that one Idx (i.e. only top-level structure is considered).
static Type *getRetComponentType(const Function *F, unsigned Idx) { … }

/// Checks Use for liveness in LiveValues. If Use is not live, it adds Use to
/// the MaybeLiveUses argument. Returns the determined liveness of Use.
DeadArgumentEliminationPass::Liveness
DeadArgumentEliminationPass::markIfNotLive(RetOrArg Use,
                                           UseVector &MaybeLiveUses) { … }

/// Looks at a single use of an argument or return value and determines if it
/// should be alive or not. Adds this use to MaybeLiveUses if it causes the
/// used value to become MaybeLive.
///
/// RetValNum is the return value number to use when this use is used in a
/// return instruction. This is used in the recursion, you should always leave
/// it at 0.
DeadArgumentEliminationPass::Liveness
DeadArgumentEliminationPass::surveyUse(const Use *U, UseVector &MaybeLiveUses,
                                       unsigned RetValNum) { … }

/// Looks at all the uses of the given value
/// Returns the Liveness deduced from the uses of this value.
///
/// Adds all uses that cause the result to be MaybeLive to MaybeLiveRetUses. If
/// the result is Live, MaybeLiveUses might be modified but its content should
/// be ignored (since it might not be complete).
DeadArgumentEliminationPass::Liveness
DeadArgumentEliminationPass::surveyUses(const Value *V,
                                        UseVector &MaybeLiveUses) { … }

/// Performs the initial survey of the specified function, checking out whether
/// it uses any of its incoming arguments or whether any callers use the return
/// value. This fills in the LiveValues set and Uses map.
///
/// We consider arguments of non-internal functions to be intrinsically alive as
/// well as arguments to functions which have their "address taken".
void DeadArgumentEliminationPass::surveyFunction(const Function &F) { … }

/// Marks the liveness of RA depending on L. If L is MaybeLive, it also takes
/// all uses in MaybeLiveUses and records them in Uses, such that RA will be
/// marked live if any use in MaybeLiveUses gets marked live later on.
void DeadArgumentEliminationPass::markValue(const RetOrArg &RA, Liveness L,
                                            const UseVector &MaybeLiveUses) { … }

/// Mark the given Function as alive, meaning that it cannot be changed in any
/// way. Additionally, mark any values that are used as this function's
/// parameters or by its return values (according to Uses) live as well.
void DeadArgumentEliminationPass::markLive(const Function &F) { … }

/// Mark the given return value or argument as live. Additionally, mark any
/// values that are used by this value (according to Uses) live as well.
void DeadArgumentEliminationPass::markLive(const RetOrArg &RA) { … }

bool DeadArgumentEliminationPass::isLive(const RetOrArg &RA) { … }

/// Given that RA is a live value, propagate it's liveness to any other values
/// it uses (according to Uses).
void DeadArgumentEliminationPass::propagateLiveness(const RetOrArg &RA) { … }

/// Remove any arguments and return values from F that are not in LiveValues.
/// Transform the function and all the callees of the function to not have these
/// arguments and return values.
bool DeadArgumentEliminationPass::removeDeadStuffFromFunction(Function *F) { … }

void DeadArgumentEliminationPass::propagateVirtMustcallLiveness(
    const Module &M) { … }

PreservedAnalyses DeadArgumentEliminationPass::run(Module &M,
                                                   ModuleAnalysisManager &) { … }
llvm/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
