Loads.h revision 3574eca1b02600bac4e625297f4ecf745f4c4f32 
1//===- Loads.h - Local load analysis --------------------------------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file declares simple local analyses for load instructions.
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_ANALYSIS_LOADS_H
15#define LLVM_ANALYSIS_LOADS_H
16
17#include "llvm/BasicBlock.h"
18
19namespace llvm {
20
21class AliasAnalysis;
22class DataLayout;
23class MDNode;
24
25/// isSafeToLoadUnconditionally - Return true if we know that executing a load
26/// from this value cannot trap.  If it is not obviously safe to load from the
27/// specified pointer, we do a quick local scan of the basic block containing
28/// ScanFrom, to determine if the address is already accessed.
29bool isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom,
30                                 unsigned Align, const DataLayout *TD = 0);
31
32/// FindAvailableLoadedValue - Scan the ScanBB block backwards (starting at
33/// the instruction before ScanFrom) checking to see if we have the value at
34/// the memory address *Ptr locally available within a small number of
35///  instructions. If the value is available, return it.
36///
37/// If not, return the iterator for the last validated instruction that the
38/// value would be live through.  If we scanned the entire block and didn't
39/// find something that invalidates *Ptr or provides it, ScanFrom would be
40/// left at begin() and this returns null.  ScanFrom could also be left
41///
42/// MaxInstsToScan specifies the maximum instructions to scan in the block.
43/// If it is set to 0, it will scan the whole block. You can also optionally
44/// specify an alias analysis implementation, which makes this more precise.
45///
46/// If TBAATag is non-null and a load or store is found, the TBAA tag from the
47/// load or store is recorded there.  If there is no TBAA tag or if no access
48/// is found, it is left unmodified.
49Value *FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB,
50                                BasicBlock::iterator &ScanFrom,
51                                unsigned MaxInstsToScan = 6,
52                                AliasAnalysis *AA = 0,
53                                MDNode **TBAATag = 0);
54
55}
56
57#endif
58