CallPromotionUtils.h

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//===- CallPromotionUtils.h - Utilities for call promotion ------*- C++ -*-===//
//
// 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 file declares utilities useful for promoting indirect call sites to
// direct call sites.
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_TRANSFORMS_UTILS_CALLPROMOTIONUTILS_H
#define LLVM_TRANSFORMS_UTILS_CALLPROMOTIONUTILS_H
 
namespace llvm {
template <typename T> class ArrayRef;
class Constant;
class CallBase;
class CastInst;
class Function;
class Instruction;
class MDNode;
class Value;
 
/// Return true if the given indirect call site can be made to call \p Callee.
///
/// This function ensures that the number and type of the call site's arguments
/// and return value match those of the given function. If the types do not
/// match exactly, they must at least be bitcast compatible. If \p FailureReason
/// is non-null and the indirect call cannot be promoted, the failure reason
/// will be stored in it.
bool isLegalToPromote(const CallBase &CB, Function *Callee,
                      const char **FailureReason = nullptr);
 
/// Promote the given indirect call site to unconditionally call \p Callee.
///
/// This function promotes the given call site, returning the direct call or
/// invoke instruction. If the function type of the call site doesn't match that
/// of the callee, bitcast instructions are inserted where appropriate. If \p
/// RetBitCast is non-null, it will be used to store the return value bitcast,
/// if created.
CallBase &promoteCall(CallBase &CB, Function *Callee,
                      CastInst **RetBitCast = nullptr);
 
/// Promote the given indirect call site to conditionally call \p Callee. The
/// promoted direct call instruction is predicated on `CB.getCalledOperand() ==
/// Callee`.
///
/// This function creates an if-then-else structure at the location of the call
/// site. The original call site is moved into the "else" block. A clone of the
/// indirect call site is promoted, placed in the "then" block, and returned. If
/// \p BranchWeights is non-null, it will be used to set !prof metadata on the
/// new conditional branch.
CallBase &promoteCallWithIfThenElse(CallBase &CB, Function *Callee,
                                    MDNode *BranchWeights = nullptr);
 
/// This is similar to `promoteCallWithIfThenElse` except that the condition to
/// promote a virtual call is that \p VPtr is the same as any of \p
/// AddressPoints.
///
/// This function is expected to be used on virtual calls (a subset of indirect
/// calls). \p VPtr is the virtual table address stored in the objects, and
/// \p AddressPoints contains vtable address points. A vtable address point is
/// a location inside the vtable that's referenced by vpointer in C++ objects.
///
/// TODO: sink the address-calculation instructions of indirect callee to the
/// indirect call fallback after transformation.
CallBase &promoteCallWithVTableCmp(CallBase &CB, Instruction *VPtr,
                                   Function *Callee,
                                   ArrayRef<Constant *> AddressPoints,
                                   MDNode *BranchWeights);
 
/// Try to promote (devirtualize) a virtual call on an Alloca. Return true on
/// success.
///
/// Look for a pattern like:
///
///  %o = alloca %class.Impl
///  %1 = getelementptr %class.Impl, %class.Impl* %o, i64 0, i32 0, i32 0
///  store i32 (...)** bitcast (i8** getelementptr inbounds
///      ({ [3 x i8*] }, { [3 x i8*] }* @_ZTV4Impl, i64 0, inrange i32 0, i64 2)
///      to i32 (...)**), i32 (...)*** %1
///  %2 = getelementptr inbounds %class.Impl, %class.Impl* %o, i64 0, i32 0
///  %3 = bitcast %class.Interface* %2 to void (%class.Interface*)***
///  %vtable.i = load void (%class.Interface*)**, void (%class.Interface*)*** %3
///  %4 = load void (%class.Interface*)*, void (%class.Interface*)** %vtable.i
///  call void %4(%class.Interface* nonnull %2)
///
/// @_ZTV4Impl = linkonce_odr dso_local unnamed_addr constant { [3 x i8*] }
///     { [3 x i8*]
///     [i8* null, i8* bitcast ({ i8*, i8*, i8* }* @_ZTI4Impl to i8*),
///     i8* bitcast (void (%class.Impl*)* @_ZN4Impl3RunEv to i8*)] }
///
bool tryPromoteCall(CallBase &CB);
 
/// Predicate and clone the given call site.
///
/// This function creates an if-then-else structure at the location of the
/// call site. The "if" condition compares the call site's called value to
/// the given callee. The original call site is moved into the "else" block,
/// and a clone of the call site is placed in the "then" block. The cloned
/// instruction is returned.
CallBase &versionCallSite(CallBase &CB, Value *Callee, MDNode *BranchWeights);
 
} // end namespace llvm
 
#endif // LLVM_TRANSFORMS_UTILS_CALLPROMOTIONUTILS_H