llvm-project/llvm/lib/Analysis/CFLSteensAliasAnalysis.cpp

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//===- CFLSteensAliasAnalysis.cpp - Unification-based Alias Analysis ------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements a CFL-base, summary-based alias analysis algorithm. It
// does not depend on types. The algorithm is a mixture of the one described in
// "Demand-driven alias analysis for C" by Xin Zheng and Radu Rugina, and "Fast
// algorithms for Dyck-CFL-reachability with applications to Alias Analysis" by
// Zhang Q, Lyu M R, Yuan H, and Su Z. -- to summarize the papers, we build a
// graph of the uses of a variable, where each node is a memory location, and
// each edge is an action that happened on that memory location. The "actions"
// can be one of Dereference, Reference, or Assign. The precision of this
// analysis is roughly the same as that of an one level context-sensitive
// Steensgaard's algorithm.
//
// Two variables are considered as aliasing iff you can reach one value's node
// from the other value's node and the language formed by concatenating all of
// the edge labels (actions) conforms to a context-free grammar.
//
// Because this algorithm requires a graph search on each query, we execute the
// algorithm outlined in "Fast algorithms..." (mentioned above)
// in order to transform the graph into sets of variables that may alias in
// ~nlogn time (n = number of variables), which makes queries take constant
// time.
//===----------------------------------------------------------------------===//
// N.B. AliasAnalysis as a whole is phrased as a FunctionPass at the moment, and
// CFLSteensAA is interprocedural. This is *technically* A Bad Thing, because
// FunctionPasses are only allowed to inspect the Function that they're being
// run on. Realistically, this likely isn't a problem until we allow
// FunctionPasses to run concurrently.
#include "llvm/Analysis/CFLSteensAliasAnalysis.h"
#include "AliasAnalysisSummary.h"
#include "CFLGraph.h"
#include "StratifiedSets.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Value.h"
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <limits>
#include <memory>
#include <utility>
using namespace llvm;
using namespace llvm::cflaa;
#define DEBUG_TYPE "cfl-steens-aa"
CFLSteensAAResult::CFLSteensAAResult(const TargetLibraryInfo &TLI)
: AAResultBase(), TLI(TLI) {}
CFLSteensAAResult::CFLSteensAAResult(CFLSteensAAResult &&Arg)
: AAResultBase(std::move(Arg)), TLI(Arg.TLI) {}
CFLSteensAAResult::~CFLSteensAAResult() = default;
/// Information we have about a function and would like to keep around.
class CFLSteensAAResult::FunctionInfo {
StratifiedSets<InstantiatedValue> Sets;
AliasSummary Summary;
public:
FunctionInfo(Function &Fn, const SmallVectorImpl<Value *> &RetVals,
StratifiedSets<InstantiatedValue> S);
const StratifiedSets<InstantiatedValue> &getStratifiedSets() const {
return Sets;
}
const AliasSummary &getAliasSummary() const { return Summary; }
};
const StratifiedIndex StratifiedLink::SetSentinel =
std::numeric_limits<StratifiedIndex>::max();
//===----------------------------------------------------------------------===//
// Function declarations that require types defined in the namespace above
//===----------------------------------------------------------------------===//
/// Determines whether it would be pointless to add the given Value to our sets.
static bool canSkipAddingToSets(Value *Val) {
// Constants can share instances, which may falsely unify multiple
// sets, e.g. in
// store i32* null, i32** %ptr1
// store i32* null, i32** %ptr2
// clearly ptr1 and ptr2 should not be unified into the same set, so
// we should filter out the (potentially shared) instance to
// i32* null.
if (isa<Constant>(Val)) {
// TODO: Because all of these things are constant, we can determine whether
// the data is *actually* mutable at graph building time. This will probably
// come for free/cheap with offset awareness.
bool CanStoreMutableData = isa<GlobalValue>(Val) ||
isa<ConstantExpr>(Val) ||
isa<ConstantAggregate>(Val);
return !CanStoreMutableData;
}
return false;
}
CFLSteensAAResult::FunctionInfo::FunctionInfo(
Function &Fn, const SmallVectorImpl<Value *> &RetVals,
StratifiedSets<InstantiatedValue> S)
: Sets(std::move(S)) {
// Historically, an arbitrary upper-bound of 50 args was selected. We may want
// to remove this if it doesn't really matter in practice.
if (Fn.arg_size() > MaxSupportedArgsInSummary)
return;
DenseMap<StratifiedIndex, InterfaceValue> InterfaceMap;
// Our intention here is to record all InterfaceValues that share the same
// StratifiedIndex in RetParamRelations. For each valid InterfaceValue, we
// have its StratifiedIndex scanned here and check if the index is presented
// in InterfaceMap: if it is not, we add the correspondence to the map;
// otherwise, an aliasing relation is found and we add it to
// RetParamRelations.
auto AddToRetParamRelations = [&](unsigned InterfaceIndex,
StratifiedIndex SetIndex) {
unsigned Level = 0;
while (true) {
InterfaceValue CurrValue{InterfaceIndex, Level};
auto Itr = InterfaceMap.find(SetIndex);
if (Itr != InterfaceMap.end()) {
if (CurrValue != Itr->second)
Summary.RetParamRelations.push_back(
ExternalRelation{CurrValue, Itr->second, UnknownOffset});
break;
}
auto &Link = Sets.getLink(SetIndex);
InterfaceMap.insert(std::make_pair(SetIndex, CurrValue));
auto ExternalAttrs = getExternallyVisibleAttrs(Link.Attrs);
if (ExternalAttrs.any())
Summary.RetParamAttributes.push_back(
ExternalAttribute{CurrValue, ExternalAttrs});
if (!Link.hasBelow())
break;
++Level;
SetIndex = Link.Below;
}
};
// Populate RetParamRelations for return values
for (auto *RetVal : RetVals) {
assert(RetVal != nullptr);
assert(RetVal->getType()->isPointerTy());
auto RetInfo = Sets.find(InstantiatedValue{RetVal, 0});
if (RetInfo.hasValue())
AddToRetParamRelations(0, RetInfo->Index);
}
// Populate RetParamRelations for parameters
unsigned I = 0;
for (auto &Param : Fn.args()) {
if (Param.getType()->isPointerTy()) {
auto ParamInfo = Sets.find(InstantiatedValue{&Param, 0});
if (ParamInfo.hasValue())
AddToRetParamRelations(I + 1, ParamInfo->Index);
}
++I;
}
}
// Builds the graph + StratifiedSets for a function.
CFLSteensAAResult::FunctionInfo CFLSteensAAResult::buildSetsFrom(Function *Fn) {
CFLGraphBuilder<CFLSteensAAResult> GraphBuilder(*this, TLI, *Fn);
StratifiedSetsBuilder<InstantiatedValue> SetBuilder;
// Add all CFLGraph nodes and all Dereference edges to StratifiedSets
auto &Graph = GraphBuilder.getCFLGraph();
for (const auto &Mapping : Graph.value_mappings()) {
auto Val = Mapping.first;
if (canSkipAddingToSets(Val))
continue;
auto &ValueInfo = Mapping.second;
assert(ValueInfo.getNumLevels() > 0);
SetBuilder.add(InstantiatedValue{Val, 0});
SetBuilder.noteAttributes(InstantiatedValue{Val, 0},
ValueInfo.getNodeInfoAtLevel(0).Attr);
for (unsigned I = 0, E = ValueInfo.getNumLevels() - 1; I < E; ++I) {
SetBuilder.add(InstantiatedValue{Val, I + 1});
SetBuilder.noteAttributes(InstantiatedValue{Val, I + 1},
ValueInfo.getNodeInfoAtLevel(I + 1).Attr);
SetBuilder.addBelow(InstantiatedValue{Val, I},
InstantiatedValue{Val, I + 1});
}
}
// Add all assign edges to StratifiedSets
for (const auto &Mapping : Graph.value_mappings()) {
auto Val = Mapping.first;
if (canSkipAddingToSets(Val))
continue;
auto &ValueInfo = Mapping.second;
for (unsigned I = 0, E = ValueInfo.getNumLevels(); I < E; ++I) {
auto Src = InstantiatedValue{Val, I};
for (auto &Edge : ValueInfo.getNodeInfoAtLevel(I).Edges)
SetBuilder.addWith(Src, Edge.Other);
}
}
return FunctionInfo(*Fn, GraphBuilder.getReturnValues(), SetBuilder.build());
}
void CFLSteensAAResult::scan(Function *Fn) {
auto InsertPair = Cache.insert(std::make_pair(Fn, Optional<FunctionInfo>()));
(void)InsertPair;
assert(InsertPair.second &&
"Trying to scan a function that has already been cached");
// Note that we can't do Cache[Fn] = buildSetsFrom(Fn) here: the function call
// may get evaluated after operator[], potentially triggering a DenseMap
// resize and invalidating the reference returned by operator[]
auto FunInfo = buildSetsFrom(Fn);
Cache[Fn] = std::move(FunInfo);
Handles.emplace_front(Fn, this);
}
void CFLSteensAAResult::evict(Function *Fn) { Cache.erase(Fn); }
/// Ensures that the given function is available in the cache, and returns the
/// entry.
const Optional<CFLSteensAAResult::FunctionInfo> &
CFLSteensAAResult::ensureCached(Function *Fn) {
auto Iter = Cache.find(Fn);
if (Iter == Cache.end()) {
scan(Fn);
Iter = Cache.find(Fn);
assert(Iter != Cache.end());
assert(Iter->second.hasValue());
}
return Iter->second;
}
const AliasSummary *CFLSteensAAResult::getAliasSummary(Function &Fn) {
auto &FunInfo = ensureCached(&Fn);
if (FunInfo.hasValue())
return &FunInfo->getAliasSummary();
else
return nullptr;
}
AliasResult CFLSteensAAResult::query(const MemoryLocation &LocA,
const MemoryLocation &LocB) {
auto *ValA = const_cast<Value *>(LocA.Ptr);
auto *ValB = const_cast<Value *>(LocB.Ptr);
if (!ValA->getType()->isPointerTy() || !ValB->getType()->isPointerTy())
return NoAlias;
Function *Fn = nullptr;
Function *MaybeFnA = const_cast<Function *>(parentFunctionOfValue(ValA));
Function *MaybeFnB = const_cast<Function *>(parentFunctionOfValue(ValB));
if (!MaybeFnA && !MaybeFnB) {
// The only times this is known to happen are when globals + InlineAsm are
// involved
LLVM_DEBUG(
dbgs()
<< "CFLSteensAA: could not extract parent function information.\n");
return MayAlias;
}
if (MaybeFnA) {
Fn = MaybeFnA;
assert((!MaybeFnB || MaybeFnB == MaybeFnA) &&
"Interprocedural queries not supported");
} else {
Fn = MaybeFnB;
}
assert(Fn != nullptr);
auto &MaybeInfo = ensureCached(Fn);
assert(MaybeInfo.hasValue());
auto &Sets = MaybeInfo->getStratifiedSets();
auto MaybeA = Sets.find(InstantiatedValue{ValA, 0});
if (!MaybeA.hasValue())
return MayAlias;
auto MaybeB = Sets.find(InstantiatedValue{ValB, 0});
if (!MaybeB.hasValue())
return MayAlias;
auto SetA = *MaybeA;
auto SetB = *MaybeB;
auto AttrsA = Sets.getLink(SetA.Index).Attrs;
auto AttrsB = Sets.getLink(SetB.Index).Attrs;
// If both values are local (meaning the corresponding set has attribute
// AttrNone or AttrEscaped), then we know that CFLSteensAA fully models them:
// they may-alias each other if and only if they are in the same set.
// If at least one value is non-local (meaning it either is global/argument or
// it comes from unknown sources like integer cast), the situation becomes a
// bit more interesting. We follow three general rules described below:
// - Non-local values may alias each other
// - AttrNone values do not alias any non-local values
// - AttrEscaped do not alias globals/arguments, but they may alias
// AttrUnknown values
if (SetA.Index == SetB.Index)
return MayAlias;
if (AttrsA.none() || AttrsB.none())
return NoAlias;
if (hasUnknownOrCallerAttr(AttrsA) || hasUnknownOrCallerAttr(AttrsB))
return MayAlias;
if (isGlobalOrArgAttr(AttrsA) && isGlobalOrArgAttr(AttrsB))
return MayAlias;
return NoAlias;
}
[PM] Change the static object whose address is used to uniquely identify analyses to have a common type which is enforced rather than using a char object and a `void *` type when used as an identifier. This has a number of advantages. First, it at least helps some of the confusion raised in Justin Lebar's code review of why `void *` was being used everywhere by having a stronger type that connects to documentation about this. However, perhaps more importantly, it addresses a serious issue where the alignment of these pointer-like identifiers was unknown. This made it hard to use them in pointer-like data structures. We were already dodging this in dangerous ways to create the "all analyses" entry. In a subsequent patch I attempted to use these with TinyPtrVector and things fell apart in a very bad way. And it isn't just a compile time or type system issue. Worse than that, the actual alignment of these pointer-like opaque identifiers wasn't guaranteed to be a useful alignment as they were just characters. This change introduces a type to use as the "key" object whose address forms the opaque identifier. This both forces the objects to have proper alignment, and provides type checking that we get it right everywhere. It also makes the types somewhat less mysterious than `void *`. We could go one step further and introduce a truly opaque pointer-like type to return from the `ID()` static function rather than returning `AnalysisKey *`, but that didn't seem to be a clear win so this is just the initial change to get to a reliably typed and aligned object serving is a key for all the analyses. Thanks to Richard Smith and Justin Lebar for helping pick plausible names and avoid making this refactoring many times. =] And thanks to Sean for the super fast review! While here, I've tried to move away from the "PassID" nomenclature entirely as it wasn't really helping and is overloaded with old pass manager constructs. Now we have IDs for analyses, and key objects whose address can be used as IDs. Where possible and clear I've shortened this to just "ID". In a few places I kept "AnalysisID" to make it clear what was being identified. Differential Revision: https://reviews.llvm.org/D27031 llvm-svn: 287783
2016-11-24 01:53:26 +08:00
AnalysisKey CFLSteensAA::Key;
CFLSteensAAResult CFLSteensAA::run(Function &F, FunctionAnalysisManager &AM) {
return CFLSteensAAResult(AM.getResult<TargetLibraryAnalysis>(F));
[PM/AA] Rebuild LLVM's alias analysis infrastructure in a way compatible with the new pass manager, and no longer relying on analysis groups. This builds essentially a ground-up new AA infrastructure stack for LLVM. The core ideas are the same that are used throughout the new pass manager: type erased polymorphism and direct composition. The design is as follows: - FunctionAAResults is a type-erasing alias analysis results aggregation interface to walk a single query across a range of results from different alias analyses. Currently this is function-specific as we always assume that aliasing queries are *within* a function. - AAResultBase is a CRTP utility providing stub implementations of various parts of the alias analysis result concept, notably in several cases in terms of other more general parts of the interface. This can be used to implement only a narrow part of the interface rather than the entire interface. This isn't really ideal, this logic should be hoisted into FunctionAAResults as currently it will cause a significant amount of redundant work, but it faithfully models the behavior of the prior infrastructure. - All the alias analysis passes are ported to be wrapper passes for the legacy PM and new-style analysis passes for the new PM with a shared result object. In some cases (most notably CFL), this is an extremely naive approach that we should revisit when we can specialize for the new pass manager. - BasicAA has been restructured to reflect that it is much more fundamentally a function analysis because it uses dominator trees and loop info that need to be constructed for each function. All of the references to getting alias analysis results have been updated to use the new aggregation interface. All the preservation and other pass management code has been updated accordingly. The way the FunctionAAResultsWrapperPass works is to detect the available alias analyses when run, and add them to the results object. This means that we should be able to continue to respect when various passes are added to the pipeline, for example adding CFL or adding TBAA passes should just cause their results to be available and to get folded into this. The exception to this rule is BasicAA which really needs to be a function pass due to using dominator trees and loop info. As a consequence, the FunctionAAResultsWrapperPass directly depends on BasicAA and always includes it in the aggregation. This has significant implications for preserving analyses. Generally, most passes shouldn't bother preserving FunctionAAResultsWrapperPass because rebuilding the results just updates the set of known AA passes. The exception to this rule are LoopPass instances which need to preserve all the function analyses that the loop pass manager will end up needing. This means preserving both BasicAAWrapperPass and the aggregating FunctionAAResultsWrapperPass. Now, when preserving an alias analysis, you do so by directly preserving that analysis. This is only necessary for non-immutable-pass-provided alias analyses though, and there are only three of interest: BasicAA, GlobalsAA (formerly GlobalsModRef), and SCEVAA. Usually BasicAA is preserved when needed because it (like DominatorTree and LoopInfo) is marked as a CFG-only pass. I've expanded GlobalsAA into the preserved set everywhere we previously were preserving all of AliasAnalysis, and I've added SCEVAA in the intersection of that with where we preserve SCEV itself. One significant challenge to all of this is that the CGSCC passes were actually using the alias analysis implementations by taking advantage of a pretty amazing set of loop holes in the old pass manager's analysis management code which allowed analysis groups to slide through in many cases. Moving away from analysis groups makes this problem much more obvious. To fix it, I've leveraged the flexibility the design of the new PM components provides to just directly construct the relevant alias analyses for the relevant functions in the IPO passes that need them. This is a bit hacky, but should go away with the new pass manager, and is already in many ways cleaner than the prior state. Another significant challenge is that various facilities of the old alias analysis infrastructure just don't fit any more. The most significant of these is the alias analysis 'counter' pass. That pass relied on the ability to snoop on AA queries at different points in the analysis group chain. Instead, I'm planning to build printing functionality directly into the aggregation layer. I've not included that in this patch merely to keep it smaller. Note that all of this needs a nearly complete rewrite of the AA documentation. I'm planning to do that, but I'd like to make sure the new design settles, and to flesh out a bit more of what it looks like in the new pass manager first. Differential Revision: http://reviews.llvm.org/D12080 llvm-svn: 247167
2015-09-10 01:55:00 +08:00
}
char CFLSteensAAWrapperPass::ID = 0;
INITIALIZE_PASS(CFLSteensAAWrapperPass, "cfl-steens-aa",
"Unification-Based CFL Alias Analysis", false, true)
[PM/AA] Rebuild LLVM's alias analysis infrastructure in a way compatible with the new pass manager, and no longer relying on analysis groups. This builds essentially a ground-up new AA infrastructure stack for LLVM. The core ideas are the same that are used throughout the new pass manager: type erased polymorphism and direct composition. The design is as follows: - FunctionAAResults is a type-erasing alias analysis results aggregation interface to walk a single query across a range of results from different alias analyses. Currently this is function-specific as we always assume that aliasing queries are *within* a function. - AAResultBase is a CRTP utility providing stub implementations of various parts of the alias analysis result concept, notably in several cases in terms of other more general parts of the interface. This can be used to implement only a narrow part of the interface rather than the entire interface. This isn't really ideal, this logic should be hoisted into FunctionAAResults as currently it will cause a significant amount of redundant work, but it faithfully models the behavior of the prior infrastructure. - All the alias analysis passes are ported to be wrapper passes for the legacy PM and new-style analysis passes for the new PM with a shared result object. In some cases (most notably CFL), this is an extremely naive approach that we should revisit when we can specialize for the new pass manager. - BasicAA has been restructured to reflect that it is much more fundamentally a function analysis because it uses dominator trees and loop info that need to be constructed for each function. All of the references to getting alias analysis results have been updated to use the new aggregation interface. All the preservation and other pass management code has been updated accordingly. The way the FunctionAAResultsWrapperPass works is to detect the available alias analyses when run, and add them to the results object. This means that we should be able to continue to respect when various passes are added to the pipeline, for example adding CFL or adding TBAA passes should just cause their results to be available and to get folded into this. The exception to this rule is BasicAA which really needs to be a function pass due to using dominator trees and loop info. As a consequence, the FunctionAAResultsWrapperPass directly depends on BasicAA and always includes it in the aggregation. This has significant implications for preserving analyses. Generally, most passes shouldn't bother preserving FunctionAAResultsWrapperPass because rebuilding the results just updates the set of known AA passes. The exception to this rule are LoopPass instances which need to preserve all the function analyses that the loop pass manager will end up needing. This means preserving both BasicAAWrapperPass and the aggregating FunctionAAResultsWrapperPass. Now, when preserving an alias analysis, you do so by directly preserving that analysis. This is only necessary for non-immutable-pass-provided alias analyses though, and there are only three of interest: BasicAA, GlobalsAA (formerly GlobalsModRef), and SCEVAA. Usually BasicAA is preserved when needed because it (like DominatorTree and LoopInfo) is marked as a CFG-only pass. I've expanded GlobalsAA into the preserved set everywhere we previously were preserving all of AliasAnalysis, and I've added SCEVAA in the intersection of that with where we preserve SCEV itself. One significant challenge to all of this is that the CGSCC passes were actually using the alias analysis implementations by taking advantage of a pretty amazing set of loop holes in the old pass manager's analysis management code which allowed analysis groups to slide through in many cases. Moving away from analysis groups makes this problem much more obvious. To fix it, I've leveraged the flexibility the design of the new PM components provides to just directly construct the relevant alias analyses for the relevant functions in the IPO passes that need them. This is a bit hacky, but should go away with the new pass manager, and is already in many ways cleaner than the prior state. Another significant challenge is that various facilities of the old alias analysis infrastructure just don't fit any more. The most significant of these is the alias analysis 'counter' pass. That pass relied on the ability to snoop on AA queries at different points in the analysis group chain. Instead, I'm planning to build printing functionality directly into the aggregation layer. I've not included that in this patch merely to keep it smaller. Note that all of this needs a nearly complete rewrite of the AA documentation. I'm planning to do that, but I'd like to make sure the new design settles, and to flesh out a bit more of what it looks like in the new pass manager first. Differential Revision: http://reviews.llvm.org/D12080 llvm-svn: 247167
2015-09-10 01:55:00 +08:00
ImmutablePass *llvm::createCFLSteensAAWrapperPass() {
return new CFLSteensAAWrapperPass();
}
[PM/AA] Rebuild LLVM's alias analysis infrastructure in a way compatible with the new pass manager, and no longer relying on analysis groups. This builds essentially a ground-up new AA infrastructure stack for LLVM. The core ideas are the same that are used throughout the new pass manager: type erased polymorphism and direct composition. The design is as follows: - FunctionAAResults is a type-erasing alias analysis results aggregation interface to walk a single query across a range of results from different alias analyses. Currently this is function-specific as we always assume that aliasing queries are *within* a function. - AAResultBase is a CRTP utility providing stub implementations of various parts of the alias analysis result concept, notably in several cases in terms of other more general parts of the interface. This can be used to implement only a narrow part of the interface rather than the entire interface. This isn't really ideal, this logic should be hoisted into FunctionAAResults as currently it will cause a significant amount of redundant work, but it faithfully models the behavior of the prior infrastructure. - All the alias analysis passes are ported to be wrapper passes for the legacy PM and new-style analysis passes for the new PM with a shared result object. In some cases (most notably CFL), this is an extremely naive approach that we should revisit when we can specialize for the new pass manager. - BasicAA has been restructured to reflect that it is much more fundamentally a function analysis because it uses dominator trees and loop info that need to be constructed for each function. All of the references to getting alias analysis results have been updated to use the new aggregation interface. All the preservation and other pass management code has been updated accordingly. The way the FunctionAAResultsWrapperPass works is to detect the available alias analyses when run, and add them to the results object. This means that we should be able to continue to respect when various passes are added to the pipeline, for example adding CFL or adding TBAA passes should just cause their results to be available and to get folded into this. The exception to this rule is BasicAA which really needs to be a function pass due to using dominator trees and loop info. As a consequence, the FunctionAAResultsWrapperPass directly depends on BasicAA and always includes it in the aggregation. This has significant implications for preserving analyses. Generally, most passes shouldn't bother preserving FunctionAAResultsWrapperPass because rebuilding the results just updates the set of known AA passes. The exception to this rule are LoopPass instances which need to preserve all the function analyses that the loop pass manager will end up needing. This means preserving both BasicAAWrapperPass and the aggregating FunctionAAResultsWrapperPass. Now, when preserving an alias analysis, you do so by directly preserving that analysis. This is only necessary for non-immutable-pass-provided alias analyses though, and there are only three of interest: BasicAA, GlobalsAA (formerly GlobalsModRef), and SCEVAA. Usually BasicAA is preserved when needed because it (like DominatorTree and LoopInfo) is marked as a CFG-only pass. I've expanded GlobalsAA into the preserved set everywhere we previously were preserving all of AliasAnalysis, and I've added SCEVAA in the intersection of that with where we preserve SCEV itself. One significant challenge to all of this is that the CGSCC passes were actually using the alias analysis implementations by taking advantage of a pretty amazing set of loop holes in the old pass manager's analysis management code which allowed analysis groups to slide through in many cases. Moving away from analysis groups makes this problem much more obvious. To fix it, I've leveraged the flexibility the design of the new PM components provides to just directly construct the relevant alias analyses for the relevant functions in the IPO passes that need them. This is a bit hacky, but should go away with the new pass manager, and is already in many ways cleaner than the prior state. Another significant challenge is that various facilities of the old alias analysis infrastructure just don't fit any more. The most significant of these is the alias analysis 'counter' pass. That pass relied on the ability to snoop on AA queries at different points in the analysis group chain. Instead, I'm planning to build printing functionality directly into the aggregation layer. I've not included that in this patch merely to keep it smaller. Note that all of this needs a nearly complete rewrite of the AA documentation. I'm planning to do that, but I'd like to make sure the new design settles, and to flesh out a bit more of what it looks like in the new pass manager first. Differential Revision: http://reviews.llvm.org/D12080 llvm-svn: 247167
2015-09-10 01:55:00 +08:00
CFLSteensAAWrapperPass::CFLSteensAAWrapperPass() : ImmutablePass(ID) {
initializeCFLSteensAAWrapperPassPass(*PassRegistry::getPassRegistry());
[PM/AA] Rebuild LLVM's alias analysis infrastructure in a way compatible with the new pass manager, and no longer relying on analysis groups. This builds essentially a ground-up new AA infrastructure stack for LLVM. The core ideas are the same that are used throughout the new pass manager: type erased polymorphism and direct composition. The design is as follows: - FunctionAAResults is a type-erasing alias analysis results aggregation interface to walk a single query across a range of results from different alias analyses. Currently this is function-specific as we always assume that aliasing queries are *within* a function. - AAResultBase is a CRTP utility providing stub implementations of various parts of the alias analysis result concept, notably in several cases in terms of other more general parts of the interface. This can be used to implement only a narrow part of the interface rather than the entire interface. This isn't really ideal, this logic should be hoisted into FunctionAAResults as currently it will cause a significant amount of redundant work, but it faithfully models the behavior of the prior infrastructure. - All the alias analysis passes are ported to be wrapper passes for the legacy PM and new-style analysis passes for the new PM with a shared result object. In some cases (most notably CFL), this is an extremely naive approach that we should revisit when we can specialize for the new pass manager. - BasicAA has been restructured to reflect that it is much more fundamentally a function analysis because it uses dominator trees and loop info that need to be constructed for each function. All of the references to getting alias analysis results have been updated to use the new aggregation interface. All the preservation and other pass management code has been updated accordingly. The way the FunctionAAResultsWrapperPass works is to detect the available alias analyses when run, and add them to the results object. This means that we should be able to continue to respect when various passes are added to the pipeline, for example adding CFL or adding TBAA passes should just cause their results to be available and to get folded into this. The exception to this rule is BasicAA which really needs to be a function pass due to using dominator trees and loop info. As a consequence, the FunctionAAResultsWrapperPass directly depends on BasicAA and always includes it in the aggregation. This has significant implications for preserving analyses. Generally, most passes shouldn't bother preserving FunctionAAResultsWrapperPass because rebuilding the results just updates the set of known AA passes. The exception to this rule are LoopPass instances which need to preserve all the function analyses that the loop pass manager will end up needing. This means preserving both BasicAAWrapperPass and the aggregating FunctionAAResultsWrapperPass. Now, when preserving an alias analysis, you do so by directly preserving that analysis. This is only necessary for non-immutable-pass-provided alias analyses though, and there are only three of interest: BasicAA, GlobalsAA (formerly GlobalsModRef), and SCEVAA. Usually BasicAA is preserved when needed because it (like DominatorTree and LoopInfo) is marked as a CFG-only pass. I've expanded GlobalsAA into the preserved set everywhere we previously were preserving all of AliasAnalysis, and I've added SCEVAA in the intersection of that with where we preserve SCEV itself. One significant challenge to all of this is that the CGSCC passes were actually using the alias analysis implementations by taking advantage of a pretty amazing set of loop holes in the old pass manager's analysis management code which allowed analysis groups to slide through in many cases. Moving away from analysis groups makes this problem much more obvious. To fix it, I've leveraged the flexibility the design of the new PM components provides to just directly construct the relevant alias analyses for the relevant functions in the IPO passes that need them. This is a bit hacky, but should go away with the new pass manager, and is already in many ways cleaner than the prior state. Another significant challenge is that various facilities of the old alias analysis infrastructure just don't fit any more. The most significant of these is the alias analysis 'counter' pass. That pass relied on the ability to snoop on AA queries at different points in the analysis group chain. Instead, I'm planning to build printing functionality directly into the aggregation layer. I've not included that in this patch merely to keep it smaller. Note that all of this needs a nearly complete rewrite of the AA documentation. I'm planning to do that, but I'd like to make sure the new design settles, and to flesh out a bit more of what it looks like in the new pass manager first. Differential Revision: http://reviews.llvm.org/D12080 llvm-svn: 247167
2015-09-10 01:55:00 +08:00
}
void CFLSteensAAWrapperPass::initializePass() {
auto &TLIWP = getAnalysis<TargetLibraryInfoWrapperPass>();
Result.reset(new CFLSteensAAResult(TLIWP.getTLI()));
[PM/AA] Rebuild LLVM's alias analysis infrastructure in a way compatible with the new pass manager, and no longer relying on analysis groups. This builds essentially a ground-up new AA infrastructure stack for LLVM. The core ideas are the same that are used throughout the new pass manager: type erased polymorphism and direct composition. The design is as follows: - FunctionAAResults is a type-erasing alias analysis results aggregation interface to walk a single query across a range of results from different alias analyses. Currently this is function-specific as we always assume that aliasing queries are *within* a function. - AAResultBase is a CRTP utility providing stub implementations of various parts of the alias analysis result concept, notably in several cases in terms of other more general parts of the interface. This can be used to implement only a narrow part of the interface rather than the entire interface. This isn't really ideal, this logic should be hoisted into FunctionAAResults as currently it will cause a significant amount of redundant work, but it faithfully models the behavior of the prior infrastructure. - All the alias analysis passes are ported to be wrapper passes for the legacy PM and new-style analysis passes for the new PM with a shared result object. In some cases (most notably CFL), this is an extremely naive approach that we should revisit when we can specialize for the new pass manager. - BasicAA has been restructured to reflect that it is much more fundamentally a function analysis because it uses dominator trees and loop info that need to be constructed for each function. All of the references to getting alias analysis results have been updated to use the new aggregation interface. All the preservation and other pass management code has been updated accordingly. The way the FunctionAAResultsWrapperPass works is to detect the available alias analyses when run, and add them to the results object. This means that we should be able to continue to respect when various passes are added to the pipeline, for example adding CFL or adding TBAA passes should just cause their results to be available and to get folded into this. The exception to this rule is BasicAA which really needs to be a function pass due to using dominator trees and loop info. As a consequence, the FunctionAAResultsWrapperPass directly depends on BasicAA and always includes it in the aggregation. This has significant implications for preserving analyses. Generally, most passes shouldn't bother preserving FunctionAAResultsWrapperPass because rebuilding the results just updates the set of known AA passes. The exception to this rule are LoopPass instances which need to preserve all the function analyses that the loop pass manager will end up needing. This means preserving both BasicAAWrapperPass and the aggregating FunctionAAResultsWrapperPass. Now, when preserving an alias analysis, you do so by directly preserving that analysis. This is only necessary for non-immutable-pass-provided alias analyses though, and there are only three of interest: BasicAA, GlobalsAA (formerly GlobalsModRef), and SCEVAA. Usually BasicAA is preserved when needed because it (like DominatorTree and LoopInfo) is marked as a CFG-only pass. I've expanded GlobalsAA into the preserved set everywhere we previously were preserving all of AliasAnalysis, and I've added SCEVAA in the intersection of that with where we preserve SCEV itself. One significant challenge to all of this is that the CGSCC passes were actually using the alias analysis implementations by taking advantage of a pretty amazing set of loop holes in the old pass manager's analysis management code which allowed analysis groups to slide through in many cases. Moving away from analysis groups makes this problem much more obvious. To fix it, I've leveraged the flexibility the design of the new PM components provides to just directly construct the relevant alias analyses for the relevant functions in the IPO passes that need them. This is a bit hacky, but should go away with the new pass manager, and is already in many ways cleaner than the prior state. Another significant challenge is that various facilities of the old alias analysis infrastructure just don't fit any more. The most significant of these is the alias analysis 'counter' pass. That pass relied on the ability to snoop on AA queries at different points in the analysis group chain. Instead, I'm planning to build printing functionality directly into the aggregation layer. I've not included that in this patch merely to keep it smaller. Note that all of this needs a nearly complete rewrite of the AA documentation. I'm planning to do that, but I'd like to make sure the new design settles, and to flesh out a bit more of what it looks like in the new pass manager first. Differential Revision: http://reviews.llvm.org/D12080 llvm-svn: 247167
2015-09-10 01:55:00 +08:00
}
void CFLSteensAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
[PM/AA] Rebuild LLVM's alias analysis infrastructure in a way compatible with the new pass manager, and no longer relying on analysis groups. This builds essentially a ground-up new AA infrastructure stack for LLVM. The core ideas are the same that are used throughout the new pass manager: type erased polymorphism and direct composition. The design is as follows: - FunctionAAResults is a type-erasing alias analysis results aggregation interface to walk a single query across a range of results from different alias analyses. Currently this is function-specific as we always assume that aliasing queries are *within* a function. - AAResultBase is a CRTP utility providing stub implementations of various parts of the alias analysis result concept, notably in several cases in terms of other more general parts of the interface. This can be used to implement only a narrow part of the interface rather than the entire interface. This isn't really ideal, this logic should be hoisted into FunctionAAResults as currently it will cause a significant amount of redundant work, but it faithfully models the behavior of the prior infrastructure. - All the alias analysis passes are ported to be wrapper passes for the legacy PM and new-style analysis passes for the new PM with a shared result object. In some cases (most notably CFL), this is an extremely naive approach that we should revisit when we can specialize for the new pass manager. - BasicAA has been restructured to reflect that it is much more fundamentally a function analysis because it uses dominator trees and loop info that need to be constructed for each function. All of the references to getting alias analysis results have been updated to use the new aggregation interface. All the preservation and other pass management code has been updated accordingly. The way the FunctionAAResultsWrapperPass works is to detect the available alias analyses when run, and add them to the results object. This means that we should be able to continue to respect when various passes are added to the pipeline, for example adding CFL or adding TBAA passes should just cause their results to be available and to get folded into this. The exception to this rule is BasicAA which really needs to be a function pass due to using dominator trees and loop info. As a consequence, the FunctionAAResultsWrapperPass directly depends on BasicAA and always includes it in the aggregation. This has significant implications for preserving analyses. Generally, most passes shouldn't bother preserving FunctionAAResultsWrapperPass because rebuilding the results just updates the set of known AA passes. The exception to this rule are LoopPass instances which need to preserve all the function analyses that the loop pass manager will end up needing. This means preserving both BasicAAWrapperPass and the aggregating FunctionAAResultsWrapperPass. Now, when preserving an alias analysis, you do so by directly preserving that analysis. This is only necessary for non-immutable-pass-provided alias analyses though, and there are only three of interest: BasicAA, GlobalsAA (formerly GlobalsModRef), and SCEVAA. Usually BasicAA is preserved when needed because it (like DominatorTree and LoopInfo) is marked as a CFG-only pass. I've expanded GlobalsAA into the preserved set everywhere we previously were preserving all of AliasAnalysis, and I've added SCEVAA in the intersection of that with where we preserve SCEV itself. One significant challenge to all of this is that the CGSCC passes were actually using the alias analysis implementations by taking advantage of a pretty amazing set of loop holes in the old pass manager's analysis management code which allowed analysis groups to slide through in many cases. Moving away from analysis groups makes this problem much more obvious. To fix it, I've leveraged the flexibility the design of the new PM components provides to just directly construct the relevant alias analyses for the relevant functions in the IPO passes that need them. This is a bit hacky, but should go away with the new pass manager, and is already in many ways cleaner than the prior state. Another significant challenge is that various facilities of the old alias analysis infrastructure just don't fit any more. The most significant of these is the alias analysis 'counter' pass. That pass relied on the ability to snoop on AA queries at different points in the analysis group chain. Instead, I'm planning to build printing functionality directly into the aggregation layer. I've not included that in this patch merely to keep it smaller. Note that all of this needs a nearly complete rewrite of the AA documentation. I'm planning to do that, but I'd like to make sure the new design settles, and to flesh out a bit more of what it looks like in the new pass manager first. Differential Revision: http://reviews.llvm.org/D12080 llvm-svn: 247167
2015-09-10 01:55:00 +08:00
AU.setPreservesAll();
AU.addRequired<TargetLibraryInfoWrapperPass>();
}