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//===-- ARMBasicBlockInfo.h - Basic Block Information -----------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// Utility functions and data structure for computing block size.
#include "llvm/Support/MathExtras.h"
#include <algorithm>
#include <cstdint>
namespace llvm {
/// UnknownPadding - Return the worst case padding that could result from
/// unknown offset bits. This does not include alignment padding caused by
/// known offset bits.
/// @param LogAlign log2(alignment)
/// @param KnownBits Number of known low offset bits.
inline unsigned UnknownPadding(unsigned LogAlign, unsigned KnownBits) {
if (KnownBits < LogAlign)
return (1u << LogAlign) - (1u << KnownBits);
return 0;
/// BasicBlockInfo - Information about the offset and size of a single
/// basic block.
struct BasicBlockInfo {
/// Offset - Distance from the beginning of the function to the beginning
/// of this basic block.
/// Offsets are computed assuming worst case padding before an aligned
/// block. This means that subtracting basic block offsets always gives a
/// conservative estimate of the real distance which may be smaller.
/// Because worst case padding is used, the computed offset of an aligned
/// block may not actually be aligned.
unsigned Offset = 0;
/// Size - Size of the basic block in bytes. If the block contains
/// inline assembly, this is a worst case estimate.
/// The size does not include any alignment padding whether from the
/// beginning of the block, or from an aligned jump table at the end.
unsigned Size = 0;
/// KnownBits - The number of low bits in Offset that are known to be
/// exact. The remaining bits of Offset are an upper bound.
uint8_t KnownBits = 0;
/// Unalign - When non-zero, the block contains instructions (inline asm)
/// of unknown size. The real size may be smaller than Size bytes by a
/// multiple of 1 << Unalign.
uint8_t Unalign = 0;
/// PostAlign - When non-zero, the block terminator contains a .align
/// directive, so the end of the block is aligned to 1 << PostAlign
/// bytes.
uint8_t PostAlign = 0;
BasicBlockInfo() = default;
/// Compute the number of known offset bits internally to this block.
/// This number should be used to predict worst case padding when
/// splitting the block.
unsigned internalKnownBits() const {
unsigned Bits = Unalign ? Unalign : KnownBits;
// If the block size isn't a multiple of the known bits, assume the
// worst case padding.
if (Size & ((1u << Bits) - 1))
Bits = countTrailingZeros(Size);
return Bits;
/// Compute the offset immediately following this block. If LogAlign is
/// specified, return the offset the successor block will get if it has
/// this alignment.
unsigned postOffset(unsigned LogAlign = 0) const {
unsigned PO = Offset + Size;
unsigned LA = std::max(unsigned(PostAlign), LogAlign);
if (!LA)
return PO;
// Add alignment padding from the terminator.
return PO + UnknownPadding(LA, internalKnownBits());
/// Compute the number of known low bits of postOffset. If this block
/// contains inline asm, the number of known bits drops to the
/// instruction alignment. An aligned terminator may increase the number
/// of know bits.
/// If LogAlign is given, also consider the alignment of the next block.
unsigned postKnownBits(unsigned LogAlign = 0) const {
return std::max(std::max(unsigned(PostAlign), LogAlign),
} // end namespace llvm