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llvm-mirror/include/llvm/Analysis/ValueTracking.h
Duncan Sands 92b081bd42 According to my auto-simplifier the most common missed simplifications in
optimized code are:
  (non-negative number)+(power-of-two) != 0 -> true
and
  (x | 1) != 0 -> true
Instcombine knows about the second one of course, but only does it if X|1
has only one use.  These fire thousands of times in the testsuite.

llvm-svn: 124183
2011-01-25 09:38:29 +00:00

164 lines
7.8 KiB
C++

//===- llvm/Analysis/ValueTracking.h - Walk computations --------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains routines that help analyze properties that chains of
// computations have.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_ANALYSIS_VALUETRACKING_H
#define LLVM_ANALYSIS_VALUETRACKING_H
#include "llvm/Support/DataTypes.h"
#include <string>
namespace llvm {
template <typename T> class SmallVectorImpl;
class Value;
class Instruction;
class APInt;
class TargetData;
/// ComputeMaskedBits - Determine which of the bits specified in Mask are
/// known to be either zero or one and return them in the KnownZero/KnownOne
/// bit sets. This code only analyzes bits in Mask, in order to short-circuit
/// processing.
///
/// This function is defined on values with integer type, values with pointer
/// type (but only if TD is non-null), and vectors of integers. In the case
/// where V is a vector, the mask, known zero, and known one values are the
/// same width as the vector element, and the bit is set only if it is true
/// for all of the elements in the vector.
void ComputeMaskedBits(Value *V, const APInt &Mask, APInt &KnownZero,
APInt &KnownOne, const TargetData *TD = 0,
unsigned Depth = 0);
/// ComputeSignBit - Determine whether the sign bit is known to be zero or
/// one. Convenience wrapper around ComputeMaskedBits.
void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
const TargetData *TD = 0, unsigned Depth = 0);
/// isPowerOfTwo - Return true if the given value is known to have exactly one
/// bit set when defined. For vectors return true if every element is known to
/// be a power of two when defined. Supports values with integer or pointer
/// type and vectors of integers.
bool isPowerOfTwo(Value *V, const TargetData *TD = 0, unsigned Depth = 0);
/// isKnownNonZero - Return true if the given value is known to be non-zero
/// when defined. For vectors return true if every element is known to be
/// non-zero when defined. Supports values with integer or pointer type and
/// vectors of integers.
bool isKnownNonZero(Value *V, const TargetData *TD = 0, unsigned Depth = 0);
/// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use
/// this predicate to simplify operations downstream. Mask is known to be
/// zero for bits that V cannot have.
///
/// This function is defined on values with integer type, values with pointer
/// type (but only if TD is non-null), and vectors of integers. In the case
/// where V is a vector, the mask, known zero, and known one values are the
/// same width as the vector element, and the bit is set only if it is true
/// for all of the elements in the vector.
bool MaskedValueIsZero(Value *V, const APInt &Mask,
const TargetData *TD = 0, unsigned Depth = 0);
/// ComputeNumSignBits - Return the number of times the sign bit of the
/// register is replicated into the other bits. We know that at least 1 bit
/// is always equal to the sign bit (itself), but other cases can give us
/// information. For example, immediately after an "ashr X, 2", we know that
/// the top 3 bits are all equal to each other, so we return 3.
///
/// 'Op' must have a scalar integer type.
///
unsigned ComputeNumSignBits(Value *Op, const TargetData *TD = 0,
unsigned Depth = 0);
/// ComputeMultiple - This function computes the integer multiple of Base that
/// equals V. If successful, it returns true and returns the multiple in
/// Multiple. If unsuccessful, it returns false. Also, if V can be
/// simplified to an integer, then the simplified V is returned in Val. Look
/// through sext only if LookThroughSExt=true.
bool ComputeMultiple(Value *V, unsigned Base, Value *&Multiple,
bool LookThroughSExt = false,
unsigned Depth = 0);
/// CannotBeNegativeZero - Return true if we can prove that the specified FP
/// value is never equal to -0.0.
///
bool CannotBeNegativeZero(const Value *V, unsigned Depth = 0);
/// isBytewiseValue - If the specified value can be set by repeating the same
/// byte in memory, return the i8 value that it is represented with. This is
/// true for all i8 values obviously, but is also true for i32 0, i32 -1,
/// i16 0xF0F0, double 0.0 etc. If the value can't be handled with a repeated
/// byte store (e.g. i16 0x1234), return null.
Value *isBytewiseValue(Value *V);
/// FindInsertedValue - Given an aggregrate and an sequence of indices, see if
/// the scalar value indexed is already around as a register, for example if
/// it were inserted directly into the aggregrate.
///
/// If InsertBefore is not null, this function will duplicate (modified)
/// insertvalues when a part of a nested struct is extracted.
Value *FindInsertedValue(Value *V,
const unsigned *idx_begin,
const unsigned *idx_end,
Instruction *InsertBefore = 0);
/// This is a convenience wrapper for finding values indexed by a single index
/// only.
inline Value *FindInsertedValue(Value *V, const unsigned Idx,
Instruction *InsertBefore = 0) {
const unsigned Idxs[1] = { Idx };
return FindInsertedValue(V, &Idxs[0], &Idxs[1], InsertBefore);
}
/// GetPointerBaseWithConstantOffset - Analyze the specified pointer to see if
/// it can be expressed as a base pointer plus a constant offset. Return the
/// base and offset to the caller.
Value *GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
const TargetData &TD);
static inline const Value *
GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset,
const TargetData &TD) {
return GetPointerBaseWithConstantOffset(const_cast<Value*>(Ptr), Offset,TD);
}
/// GetConstantStringInfo - This function computes the length of a
/// null-terminated C string pointed to by V. If successful, it returns true
/// and returns the string in Str. If unsuccessful, it returns false. If
/// StopAtNul is set to true (the default), the returned string is truncated
/// by a nul character in the global. If StopAtNul is false, the nul
/// character is included in the result string.
bool GetConstantStringInfo(const Value *V, std::string &Str,
uint64_t Offset = 0,
bool StopAtNul = true);
/// GetStringLength - If we can compute the length of the string pointed to by
/// the specified pointer, return 'len+1'. If we can't, return 0.
uint64_t GetStringLength(Value *V);
/// GetUnderlyingObject - This method strips off any GEP address adjustments
/// and pointer casts from the specified value, returning the original object
/// being addressed. Note that the returned value has pointer type if the
/// specified value does. If the MaxLookup value is non-zero, it limits the
/// number of instructions to be stripped off.
Value *GetUnderlyingObject(Value *V, const TargetData *TD = 0,
unsigned MaxLookup = 6);
static inline const Value *
GetUnderlyingObject(const Value *V, const TargetData *TD = 0,
unsigned MaxLookup = 6) {
return GetUnderlyingObject(const_cast<Value *>(V), TD, MaxLookup);
}
} // end namespace llvm
#endif