llvm-6502/lib/Analysis/PtrUseVisitor.cpp

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Add a new visitor for walking the uses of a pointer value. This visitor provides infrastructure for recursively traversing the use-graph of a pointer-producing instruction like an alloca or a malloc. It maintains a worklist of uses to visit, so it can handle very deep recursions. It automatically looks through instructions which simply translate one pointer to another (bitcasts and GEPs). It tracks the offset relative to the original pointer as long as that offset remains constant and exposes it during the visit as an APInt offset. Finally, it performs conservative escape analysis. However, currently it has some limitations that should be addressed going forward: 1) It doesn't handle vectors of pointers. 2) It doesn't provide a cheaper visitor when the constant offset tracking isn't needed. 3) It doesn't support non-instruction pointer values. The current functionality is exactly what is required to implement the SROA pointer-use visitors in terms of this one, rather than in terms of their own ad-hoc base visitor, which was always very poorly specified. SROA has been converted to use this, and the code there deleted which this utility now provides. Technically speaking, using this new visitor allows SROA to handle a few more cases than it previously did. It is now more aggressive in ignoring chains of instructions which look like they would defeat SROA, but in fact do not because they never result in a read or write of memory. While this is "neat", it shouldn't be interesting for real programs as any such chains should have been removed by others passes long before we get to SROA. As a consequence, I've not added any tests for these features -- it shouldn't be part of SROA's contract to perform such heroics. The goal is to extend the functionality of this visitor going forward, and re-use it from passes like ASan that can benefit from doing a detailed walk of the uses of a pointer. Thanks to Ben Kramer for the code review rounds and lots of help reviewing and debugging this patch. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169728 91177308-0d34-0410-b5e6-96231b3b80d8
2012-12-10 08:28:39 +00:00
//===- PtrUseVisitor.cpp - InstVisitors over a pointers uses --------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
/// \file
/// Implementation of the pointer use visitors.
///
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/PtrUseVisitor.h"
using namespace llvm;
void detail::PtrUseVisitorBase::enqueueUsers(Instruction &I) {
[C++11] Add range based accessors for the Use-Def chain of a Value. This requires a number of steps. 1) Move value_use_iterator into the Value class as an implementation detail 2) Change it to actually be a *Use* iterator rather than a *User* iterator. 3) Add an adaptor which is a User iterator that always looks through the Use to the User. 4) Wrap these in Value::use_iterator and Value::user_iterator typedefs. 5) Add the range adaptors as Value::uses() and Value::users(). 6) Update *all* of the callers to correctly distinguish between whether they wanted a use_iterator (and to explicitly dig out the User when needed), or a user_iterator which makes the Use itself totally opaque. Because #6 requires churning essentially everything that walked the Use-Def chains, I went ahead and added all of the range adaptors and switched them to range-based loops where appropriate. Also because the renaming requires at least churning every line of code, it didn't make any sense to split these up into multiple commits -- all of which would touch all of the same lies of code. The result is still not quite optimal. The Value::use_iterator is a nice regular iterator, but Value::user_iterator is an iterator over User*s rather than over the User objects themselves. As a consequence, it fits a bit awkwardly into the range-based world and it has the weird extra-dereferencing 'operator->' that so many of our iterators have. I think this could be fixed by providing something which transforms a range of T&s into a range of T*s, but that *can* be separated into another patch, and it isn't yet 100% clear whether this is the right move. However, this change gets us most of the benefit and cleans up a substantial amount of code around Use and User. =] git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203364 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-09 03:16:01 +00:00
for (Use &U : I.uses()) {
if (VisitedUses.insert(&U).second) {
Add a new visitor for walking the uses of a pointer value. This visitor provides infrastructure for recursively traversing the use-graph of a pointer-producing instruction like an alloca or a malloc. It maintains a worklist of uses to visit, so it can handle very deep recursions. It automatically looks through instructions which simply translate one pointer to another (bitcasts and GEPs). It tracks the offset relative to the original pointer as long as that offset remains constant and exposes it during the visit as an APInt offset. Finally, it performs conservative escape analysis. However, currently it has some limitations that should be addressed going forward: 1) It doesn't handle vectors of pointers. 2) It doesn't provide a cheaper visitor when the constant offset tracking isn't needed. 3) It doesn't support non-instruction pointer values. The current functionality is exactly what is required to implement the SROA pointer-use visitors in terms of this one, rather than in terms of their own ad-hoc base visitor, which was always very poorly specified. SROA has been converted to use this, and the code there deleted which this utility now provides. Technically speaking, using this new visitor allows SROA to handle a few more cases than it previously did. It is now more aggressive in ignoring chains of instructions which look like they would defeat SROA, but in fact do not because they never result in a read or write of memory. While this is "neat", it shouldn't be interesting for real programs as any such chains should have been removed by others passes long before we get to SROA. As a consequence, I've not added any tests for these features -- it shouldn't be part of SROA's contract to perform such heroics. The goal is to extend the functionality of this visitor going forward, and re-use it from passes like ASan that can benefit from doing a detailed walk of the uses of a pointer. Thanks to Ben Kramer for the code review rounds and lots of help reviewing and debugging this patch. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169728 91177308-0d34-0410-b5e6-96231b3b80d8
2012-12-10 08:28:39 +00:00
UseToVisit NewU = {
[C++11] Add range based accessors for the Use-Def chain of a Value. This requires a number of steps. 1) Move value_use_iterator into the Value class as an implementation detail 2) Change it to actually be a *Use* iterator rather than a *User* iterator. 3) Add an adaptor which is a User iterator that always looks through the Use to the User. 4) Wrap these in Value::use_iterator and Value::user_iterator typedefs. 5) Add the range adaptors as Value::uses() and Value::users(). 6) Update *all* of the callers to correctly distinguish between whether they wanted a use_iterator (and to explicitly dig out the User when needed), or a user_iterator which makes the Use itself totally opaque. Because #6 requires churning essentially everything that walked the Use-Def chains, I went ahead and added all of the range adaptors and switched them to range-based loops where appropriate. Also because the renaming requires at least churning every line of code, it didn't make any sense to split these up into multiple commits -- all of which would touch all of the same lies of code. The result is still not quite optimal. The Value::use_iterator is a nice regular iterator, but Value::user_iterator is an iterator over User*s rather than over the User objects themselves. As a consequence, it fits a bit awkwardly into the range-based world and it has the weird extra-dereferencing 'operator->' that so many of our iterators have. I think this could be fixed by providing something which transforms a range of T&s into a range of T*s, but that *can* be separated into another patch, and it isn't yet 100% clear whether this is the right move. However, this change gets us most of the benefit and cleans up a substantial amount of code around Use and User. =] git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203364 91177308-0d34-0410-b5e6-96231b3b80d8
2014-03-09 03:16:01 +00:00
UseToVisit::UseAndIsOffsetKnownPair(&U, IsOffsetKnown),
Add a new visitor for walking the uses of a pointer value. This visitor provides infrastructure for recursively traversing the use-graph of a pointer-producing instruction like an alloca or a malloc. It maintains a worklist of uses to visit, so it can handle very deep recursions. It automatically looks through instructions which simply translate one pointer to another (bitcasts and GEPs). It tracks the offset relative to the original pointer as long as that offset remains constant and exposes it during the visit as an APInt offset. Finally, it performs conservative escape analysis. However, currently it has some limitations that should be addressed going forward: 1) It doesn't handle vectors of pointers. 2) It doesn't provide a cheaper visitor when the constant offset tracking isn't needed. 3) It doesn't support non-instruction pointer values. The current functionality is exactly what is required to implement the SROA pointer-use visitors in terms of this one, rather than in terms of their own ad-hoc base visitor, which was always very poorly specified. SROA has been converted to use this, and the code there deleted which this utility now provides. Technically speaking, using this new visitor allows SROA to handle a few more cases than it previously did. It is now more aggressive in ignoring chains of instructions which look like they would defeat SROA, but in fact do not because they never result in a read or write of memory. While this is "neat", it shouldn't be interesting for real programs as any such chains should have been removed by others passes long before we get to SROA. As a consequence, I've not added any tests for these features -- it shouldn't be part of SROA's contract to perform such heroics. The goal is to extend the functionality of this visitor going forward, and re-use it from passes like ASan that can benefit from doing a detailed walk of the uses of a pointer. Thanks to Ben Kramer for the code review rounds and lots of help reviewing and debugging this patch. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169728 91177308-0d34-0410-b5e6-96231b3b80d8
2012-12-10 08:28:39 +00:00
Offset
};
Worklist.push_back(std::move(NewU));
Add a new visitor for walking the uses of a pointer value. This visitor provides infrastructure for recursively traversing the use-graph of a pointer-producing instruction like an alloca or a malloc. It maintains a worklist of uses to visit, so it can handle very deep recursions. It automatically looks through instructions which simply translate one pointer to another (bitcasts and GEPs). It tracks the offset relative to the original pointer as long as that offset remains constant and exposes it during the visit as an APInt offset. Finally, it performs conservative escape analysis. However, currently it has some limitations that should be addressed going forward: 1) It doesn't handle vectors of pointers. 2) It doesn't provide a cheaper visitor when the constant offset tracking isn't needed. 3) It doesn't support non-instruction pointer values. The current functionality is exactly what is required to implement the SROA pointer-use visitors in terms of this one, rather than in terms of their own ad-hoc base visitor, which was always very poorly specified. SROA has been converted to use this, and the code there deleted which this utility now provides. Technically speaking, using this new visitor allows SROA to handle a few more cases than it previously did. It is now more aggressive in ignoring chains of instructions which look like they would defeat SROA, but in fact do not because they never result in a read or write of memory. While this is "neat", it shouldn't be interesting for real programs as any such chains should have been removed by others passes long before we get to SROA. As a consequence, I've not added any tests for these features -- it shouldn't be part of SROA's contract to perform such heroics. The goal is to extend the functionality of this visitor going forward, and re-use it from passes like ASan that can benefit from doing a detailed walk of the uses of a pointer. Thanks to Ben Kramer for the code review rounds and lots of help reviewing and debugging this patch. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169728 91177308-0d34-0410-b5e6-96231b3b80d8
2012-12-10 08:28:39 +00:00
}
}
}
bool detail::PtrUseVisitorBase::adjustOffsetForGEP(GetElementPtrInst &GEPI) {
if (!IsOffsetKnown)
return false;
return GEPI.accumulateConstantOffset(DL, Offset);
Add a new visitor for walking the uses of a pointer value. This visitor provides infrastructure for recursively traversing the use-graph of a pointer-producing instruction like an alloca or a malloc. It maintains a worklist of uses to visit, so it can handle very deep recursions. It automatically looks through instructions which simply translate one pointer to another (bitcasts and GEPs). It tracks the offset relative to the original pointer as long as that offset remains constant and exposes it during the visit as an APInt offset. Finally, it performs conservative escape analysis. However, currently it has some limitations that should be addressed going forward: 1) It doesn't handle vectors of pointers. 2) It doesn't provide a cheaper visitor when the constant offset tracking isn't needed. 3) It doesn't support non-instruction pointer values. The current functionality is exactly what is required to implement the SROA pointer-use visitors in terms of this one, rather than in terms of their own ad-hoc base visitor, which was always very poorly specified. SROA has been converted to use this, and the code there deleted which this utility now provides. Technically speaking, using this new visitor allows SROA to handle a few more cases than it previously did. It is now more aggressive in ignoring chains of instructions which look like they would defeat SROA, but in fact do not because they never result in a read or write of memory. While this is "neat", it shouldn't be interesting for real programs as any such chains should have been removed by others passes long before we get to SROA. As a consequence, I've not added any tests for these features -- it shouldn't be part of SROA's contract to perform such heroics. The goal is to extend the functionality of this visitor going forward, and re-use it from passes like ASan that can benefit from doing a detailed walk of the uses of a pointer. Thanks to Ben Kramer for the code review rounds and lots of help reviewing and debugging this patch. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169728 91177308-0d34-0410-b5e6-96231b3b80d8
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}