215 lines
10 KiB
C++
215 lines
10 KiB
C++
//===-- ConstantFolding.h - Fold instructions into constants ----*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file declares routines for folding instructions into constants when all
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// operands are constants, for example "sub i32 1, 0" -> "1".
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//
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// Also, to supplement the basic VMCore ConstantExpr simplifications,
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// this file declares some additional folding routines that can make use of
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// DataLayout information. These functions cannot go in VMCore due to library
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// dependency issues.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ANALYSIS_CONSTANTFOLDING_H
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#define LLVM_ANALYSIS_CONSTANTFOLDING_H
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#include "llvm/Support/Compiler.h"
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#include <stdint.h>
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namespace llvm {
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namespace Intrinsic {
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using ID = unsigned;
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}
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class APInt;
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template <typename T> class ArrayRef;
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class CallBase;
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class Constant;
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class DSOLocalEquivalent;
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class DataLayout;
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class Function;
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class GlobalValue;
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class GlobalVariable;
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class Instruction;
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class TargetLibraryInfo;
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class Type;
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/// If this constant is a constant offset from a global, return the global and
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/// the constant. Because of constantexprs, this function is recursive.
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/// If the global is part of a dso_local_equivalent constant, return it through
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/// `Equiv` if it is provided.
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LLVM_ABI bool
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IsConstantOffsetFromGlobal(Constant *C, GlobalValue *&GV, APInt &Offset,
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const DataLayout &DL,
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DSOLocalEquivalent **DSOEquiv = nullptr);
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/// ConstantFoldInstruction - Try to constant fold the specified instruction.
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/// If successful, the constant result is returned, if not, null is returned.
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/// Note that this fails if not all of the operands are constant. Otherwise,
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/// this function can only fail when attempting to fold instructions like loads
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/// and stores, which have no constant expression form.
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LLVM_ABI Constant *
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ConstantFoldInstruction(const Instruction *I, const DataLayout &DL,
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const TargetLibraryInfo *TLI = nullptr);
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/// ConstantFoldConstant - Fold the constant using the specified DataLayout.
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/// This function always returns a non-null constant: Either the folding result,
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/// or the original constant if further folding is not possible.
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LLVM_ABI Constant *ConstantFoldConstant(const Constant *C, const DataLayout &DL,
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const TargetLibraryInfo *TLI = nullptr);
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/// ConstantFoldInstOperands - Attempt to constant fold an instruction with the
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/// specified operands. If successful, the constant result is returned, if not,
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/// null is returned. Note that this function can fail when attempting to
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/// fold instructions like loads and stores, which have no constant expression
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/// form.
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///
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/// In some cases, constant folding may return one value chosen from a set of
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/// multiple legal return values. For example, the exact bit pattern of NaN
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/// results is not guaranteed. Using such a result is usually only valid if
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/// all uses of the original operation are replaced by the constant-folded
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/// result. The \p AllowNonDeterministic parameter controls whether this is
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/// allowed.
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LLVM_ABI Constant *ConstantFoldInstOperands(
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const Instruction *I, ArrayRef<Constant *> Ops, const DataLayout &DL,
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const TargetLibraryInfo *TLI = nullptr, bool AllowNonDeterministic = true);
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/// Attempt to constant fold a compare instruction (icmp/fcmp) with the
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/// specified operands. Returns null or a constant expression of the specified
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/// operands on failure.
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/// Denormal inputs may be flushed based on the denormal handling mode.
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LLVM_ABI Constant *ConstantFoldCompareInstOperands(
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unsigned Predicate, Constant *LHS, Constant *RHS, const DataLayout &DL,
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const TargetLibraryInfo *TLI = nullptr, const Instruction *I = nullptr);
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/// Attempt to constant fold a unary operation with the specified operand.
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/// Returns null on failure.
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LLVM_ABI Constant *ConstantFoldUnaryOpOperand(unsigned Opcode, Constant *Op,
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const DataLayout &DL);
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/// Attempt to constant fold a binary operation with the specified operands.
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/// Returns null or a constant expression of the specified operands on failure.
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LLVM_ABI Constant *ConstantFoldBinaryOpOperands(unsigned Opcode, Constant *LHS,
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Constant *RHS,
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const DataLayout &DL);
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/// Attempt to constant fold a floating point binary operation with the
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/// specified operands, applying the denormal handling mod to the operands.
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/// Returns null or a constant expression of the specified operands on failure.
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LLVM_ABI Constant *
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ConstantFoldFPInstOperands(unsigned Opcode, Constant *LHS, Constant *RHS,
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const DataLayout &DL, const Instruction *I,
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bool AllowNonDeterministic = true);
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/// Attempt to flush float point constant according to denormal mode set in the
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/// instruction's parent function attributes. If so, return a zero with the
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/// correct sign, otherwise return the original constant. Inputs and outputs to
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/// floating point instructions can have their mode set separately, so the
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/// direction is also needed.
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///
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/// If the calling function's denormal_fpenv input mode is dynamic for the
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/// floating-point type, returns nullptr for denormal inputs.
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LLVM_ABI Constant *FlushFPConstant(Constant *Operand, const Instruction *I,
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bool IsOutput);
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/// Attempt to constant fold a cast with the specified operand. If it
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/// fails, it returns a constant expression of the specified operand.
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LLVM_ABI Constant *ConstantFoldCastOperand(unsigned Opcode, Constant *C,
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Type *DestTy, const DataLayout &DL);
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/// Constant fold a zext, sext or trunc, depending on IsSigned and whether the
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/// DestTy is wider or narrower than C. Returns nullptr on failure.
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LLVM_ABI Constant *ConstantFoldIntegerCast(Constant *C, Type *DestTy,
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bool IsSigned, const DataLayout &DL);
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/// Extract value of C at the given Offset reinterpreted as Ty. If bits past
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/// the end of C are accessed, they are assumed to be poison.
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LLVM_ABI Constant *ConstantFoldLoadFromConst(Constant *C, Type *Ty,
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const APInt &Offset,
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const DataLayout &DL);
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/// Extract value of C reinterpreted as Ty. Same as previous API with zero
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/// offset.
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LLVM_ABI Constant *ConstantFoldLoadFromConst(Constant *C, Type *Ty,
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const DataLayout &DL);
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/// Return the value that a load from C with offset Offset would produce if it
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/// is constant and determinable. If this is not determinable, return null.
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LLVM_ABI Constant *ConstantFoldLoadFromConstPtr(Constant *C, Type *Ty,
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APInt Offset,
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const DataLayout &DL);
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/// Return the value that a load from C would produce if it is constant and
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/// determinable. If this is not determinable, return null.
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LLVM_ABI Constant *ConstantFoldLoadFromConstPtr(Constant *C, Type *Ty,
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const DataLayout &DL);
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/// If C is a uniform value where all bits are the same (either all zero, all
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/// ones, all undef or all poison), return the corresponding uniform value in
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/// the new type. If the value is not uniform or the result cannot be
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/// represented, return null.
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LLVM_ABI Constant *ConstantFoldLoadFromUniformValue(Constant *C, Type *Ty,
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const DataLayout &DL);
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/// canConstantFoldCallTo - Return true if its even possible to fold a call to
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/// the specified function.
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LLVM_ABI bool canConstantFoldCallTo(const CallBase *Call, const Function *F);
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/// ConstantFoldCall - Attempt to constant fold a call to the specified function
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/// with the specified arguments, returning null if unsuccessful.
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LLVM_ABI Constant *ConstantFoldCall(const CallBase *Call, Function *F,
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ArrayRef<Constant *> Operands,
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const TargetLibraryInfo *TLI = nullptr,
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bool AllowNonDeterministic = true);
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LLVM_ABI Constant *ConstantFoldUnaryIntrinsic(Intrinsic::ID ID, Constant *Op,
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Type *Ty);
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LLVM_ABI Constant *ConstantFoldBinaryIntrinsic(Intrinsic::ID ID, Constant *LHS,
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Constant *RHS, Type *Ty);
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/// ConstantFoldLoadThroughBitcast - try to cast constant to destination type
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/// returning null if unsuccessful. Can cast pointer to pointer or pointer to
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/// integer and vice versa if their sizes are equal.
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LLVM_ABI Constant *ConstantFoldLoadThroughBitcast(Constant *C, Type *DestTy,
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const DataLayout &DL);
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/// Check whether the given call has no side-effects.
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/// Specifically checks for math routimes which sometimes set errno.
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LLVM_ABI bool isMathLibCallNoop(const CallBase *Call,
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const TargetLibraryInfo *TLI);
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LLVM_ABI Constant *ReadByteArrayFromGlobal(const GlobalVariable *GV,
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uint64_t Offset);
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struct PreservedCastFlags {
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bool NNeg = false;
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bool NUW = false;
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bool NSW = false;
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};
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/// Try to cast C to InvC losslessly, satisfying CastOp(InvC) equals C, or
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/// CastOp(InvC) is a refined value of undefined C. Will try best to
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/// preserve the flags.
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LLVM_ABI Constant *getLosslessInvCast(Constant *C, Type *InvCastTo,
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unsigned CastOp, const DataLayout &DL,
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PreservedCastFlags *Flags = nullptr);
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LLVM_ABI Constant *
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getLosslessUnsignedTrunc(Constant *C, Type *DestTy, const DataLayout &DL,
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PreservedCastFlags *Flags = nullptr);
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LLVM_ABI Constant *getLosslessSignedTrunc(Constant *C, Type *DestTy,
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const DataLayout &DL,
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PreservedCastFlags *Flags = nullptr);
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} // namespace llvm
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#endif
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