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Revert "[LICM] Make promotion faster"

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Revert 3d8f842712d49b0767832b6e3f65df2d3f19af4e
Revision triggers a miscompile sinking a store incorrectly outside a
threading loop. Detected by tsan.
Reverting while investigating.

Differential Revision: https://reviews.llvm.org/D89264
This commit is contained in:
Alina Sbirlea 2021-03-08 12:50:36 -08:00
parent 9d2b069616
commit 87fdb76351
3 changed files with 50 additions and 116 deletions
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8
include/llvm/Analysis/AliasSetTracker.h
View File

@ -20,7 +20,6 @@
#include "llvm/ADT/DenseMapInfo.h"
#include "llvm/ADT/ilist.h"
#include "llvm/ADT/ilist_node.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/MemoryLocation.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Metadata.h"
@ -39,6 +38,8 @@ class AAResults;
class AliasSetTracker;
class BasicBlock;
class LoadInst;
class Loop;
class MemorySSA;
class AnyMemSetInst;
class AnyMemTransferInst;
class raw_ostream;
@ -342,6 +343,8 @@ class AliasSetTracker {
struct ASTCallbackVHDenseMapInfo : public DenseMapInfo<Value *> {};
AAResults &AA;
MemorySSA *MSSA = nullptr;
Loop *L = nullptr;
ilist<AliasSet> AliasSets;
using PointerMapType = DenseMap<ASTCallbackVH, AliasSet::PointerRec *,
@ -354,6 +357,8 @@ public:
/// Create an empty collection of AliasSets, and use the specified alias
/// analysis object to disambiguate load and store addresses.
explicit AliasSetTracker(AAResults &AA) : AA(AA) {}
explicit AliasSetTracker(AAResults &AA, MemorySSA *MSSA, Loop *L)
: AA(AA), MSSA(MSSA), L(L) {}
~AliasSetTracker() { clear(); }
/// These methods are used to add different types of instructions to the alias
@ -378,6 +383,7 @@ public:
void add(BasicBlock &BB); // Add all instructions in basic block
void add(const AliasSetTracker &AST); // Add alias relations from another AST
void addUnknown(Instruction *I);
void addAllInstructionsInLoopUsingMSSA();
void clear();

10
lib/Analysis/AliasSetTracker.cpp
View File

@ -14,6 +14,7 @@
#include "llvm/Analysis/GuardUtils.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/MemoryLocation.h"
#include "llvm/Analysis/MemorySSA.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
@ -534,6 +535,15 @@ void AliasSetTracker::add(const AliasSetTracker &AST) {
}
}
void AliasSetTracker::addAllInstructionsInLoopUsingMSSA() {
assert(MSSA && L && "MSSA and L must be available");
for (const BasicBlock *BB : L->blocks())
if (auto *Accesses = MSSA->getBlockAccesses(BB))
for (auto &Access : *Accesses)
if (auto *MUD = dyn_cast<MemoryUseOrDef>(&Access))
add(MUD->getMemoryInst());
}
// deleteValue method - This method is used to remove a pointer value from the
// AliasSetTracker entirely. It should be used when an instruction is deleted
// from the program to update the AST. If you don't use this, you would have

148
lib/Transforms/Scalar/LICM.cpp
View File

@ -185,12 +185,6 @@ static void moveInstructionBefore(Instruction &I, Instruction &Dest,
ICFLoopSafetyInfo &SafetyInfo,
MemorySSAUpdater *MSSAU, ScalarEvolution *SE);
static void foreachMemoryAccess(MemorySSA *MSSA, Loop *L,
function_ref<void(Instruction *)> Fn);
static SmallVector<SmallSetVector<Value *, 8>, 0>
collectPromotionCandidates(MemorySSA *MSSA, AliasAnalysis *AA, Loop *L,
SmallVectorImpl<Instruction *> &MaybePromotable);
namespace {
struct LoopInvariantCodeMotion {
bool runOnLoop(Loop *L, AAResults *AA, LoopInfo *LI, DominatorTree *DT,
@ -209,6 +203,9 @@ private:
std::unique_ptr<AliasSetTracker>
collectAliasInfoForLoop(Loop *L, LoopInfo *LI, AAResults *AA);
std::unique_ptr<AliasSetTracker>
collectAliasInfoForLoopWithMSSA(Loop *L, AAResults *AA,
MemorySSAUpdater *MSSAU);
};
struct LegacyLICMPass : public LoopPass {
@ -449,48 +446,31 @@ bool LoopInvariantCodeMotion::runOnLoop(
PredIteratorCache PIC;
bool Promoted = false;
if (CurAST.get()) {
// Loop over all of the alias sets in the tracker object.
for (AliasSet &AS : *CurAST) {
// We can promote this alias set if it has a store, if it is a "Must"
// alias set, if the pointer is loop invariant, and if we are not
// eliminating any volatile loads or stores.
if (AS.isForwardingAliasSet() || !AS.isMod() || !AS.isMustAlias() ||
!L->isLoopInvariant(AS.begin()->getValue()))
continue;
assert(
!AS.empty() &&
"Must alias set should have at least one pointer element in it!");
// Build an AST using MSSA.
if (!CurAST.get())
CurAST = collectAliasInfoForLoopWithMSSA(L, AA, MSSAU.get());
SmallSetVector<Value *, 8> PointerMustAliases;
for (const auto &ASI : AS)
PointerMustAliases.insert(ASI.getValue());
// Loop over all of the alias sets in the tracker object.
for (AliasSet &AS : *CurAST) {
// We can promote this alias set if it has a store, if it is a "Must"
// alias set, if the pointer is loop invariant, and if we are not
// eliminating any volatile loads or stores.
if (AS.isForwardingAliasSet() || !AS.isMod() || !AS.isMustAlias() ||
!L->isLoopInvariant(AS.begin()->getValue()))
continue;
Promoted |= promoteLoopAccessesToScalars(
PointerMustAliases, ExitBlocks, InsertPts, MSSAInsertPts, PIC, LI,
DT, TLI, L, CurAST.get(), MSSAU.get(), &SafetyInfo, ORE);
}
} else {
SmallVector<Instruction *, 16> MaybePromotable;
foreachMemoryAccess(MSSA, L, [&](Instruction *I) {
MaybePromotable.push_back(I);
});
assert(
!AS.empty() &&
"Must alias set should have at least one pointer element in it!");
// Promoting one set of accesses may make the pointers for another set
// loop invariant, so run this in a loop (with the MaybePromotable set
// decreasing in size over time).
bool LocalPromoted;
do {
LocalPromoted = false;
for (const SmallSetVector<Value *, 8> &PointerMustAliases :
collectPromotionCandidates(MSSA, AA, L, MaybePromotable)) {
LocalPromoted |= promoteLoopAccessesToScalars(
PointerMustAliases, ExitBlocks, InsertPts, MSSAInsertPts, PIC,
LI, DT, TLI, L, /*AST*/nullptr, MSSAU.get(), &SafetyInfo, ORE);
}
Promoted |= LocalPromoted;
} while (LocalPromoted);
SmallSetVector<Value *, 8> PointerMustAliases;
for (const auto &ASI : AS)
PointerMustAliases.insert(ASI.getValue());
Promoted |= promoteLoopAccessesToScalars(
PointerMustAliases, ExitBlocks, InsertPts, MSSAInsertPts, PIC, LI,
DT, TLI, L, CurAST.get(), MSSAU.get(), &SafetyInfo, ORE);
}
// Once we have promoted values across the loop body we have to
@ -2253,77 +2233,6 @@ bool llvm::promoteLoopAccessesToScalars(
return true;
}
static void foreachMemoryAccess(MemorySSA *MSSA, Loop *L,
function_ref<void(Instruction *)> Fn) {
for (const BasicBlock *BB : L->blocks())
if (const auto *Accesses = MSSA->getBlockAccesses(BB))
for (const auto &Access : *Accesses)
if (const auto *MUD = dyn_cast<MemoryUseOrDef>(&Access))
Fn(MUD->getMemoryInst());
}
static SmallVector<SmallSetVector<Value *, 8>, 0>
collectPromotionCandidates(MemorySSA *MSSA, AliasAnalysis *AA, Loop *L,
SmallVectorImpl<Instruction *> &MaybePromotable) {
AliasSetTracker AST(*AA);
auto IsPotentiallyPromotable = [L](const Instruction *I) {
if (const auto *SI = dyn_cast<StoreInst>(I))
return L->isLoopInvariant(SI->getPointerOperand());
if (const auto *LI = dyn_cast<LoadInst>(I))
return L->isLoopInvariant(LI->getPointerOperand());
return false;
};
// Populate AST with potentially promotable accesses and remove them from
// MaybePromotable, so they will not be checked again on the next iteration.
SmallPtrSet<Value *, 16> AttemptingPromotion;
llvm::erase_if(MaybePromotable, [&](Instruction *I) {
if (IsPotentiallyPromotable(I)) {
AttemptingPromotion.insert(I);
AST.add(I);
return true;
}
return false;
});
// We're only interested in must-alias sets that contain a mod.
SmallVector<const AliasSet *, 8> Sets;
for (AliasSet &AS : AST)
if (!AS.isForwardingAliasSet() && AS.isMod() && AS.isMustAlias())
Sets.push_back(&AS);
if (Sets.empty())
return {}; // Nothing to promote...
// Discard any sets for which there is an aliasing non-promotable access.
foreachMemoryAccess(MSSA, L, [&](Instruction *I) {
if (AttemptingPromotion.contains(I))
return;
if (Optional<MemoryLocation> Loc = MemoryLocation::getOrNone(I)) {
llvm::erase_if(Sets, [&](const AliasSet *AS) {
return AS->aliasesPointer(Loc->Ptr, Loc->Size, Loc->AATags, *AA)
!= NoAlias;
});
} else {
llvm::erase_if(Sets, [&](const AliasSet *AS) {
return AS->aliasesUnknownInst(I, *AA);
});
}
});
SmallVector<SmallSetVector<Value *, 8>, 0> Result;
for (const AliasSet *Set : Sets) {
SmallSetVector<Value *, 8> PointerMustAliases;
for (const auto &ASI : *Set)
PointerMustAliases.insert(ASI.getValue());
Result.push_back(std::move(PointerMustAliases));
}
return Result;
}
/// Returns an owning pointer to an alias set which incorporates aliasing info
/// from L and all subloops of L.
std::unique_ptr<AliasSetTracker>
@ -2344,6 +2253,15 @@ LoopInvariantCodeMotion::collectAliasInfoForLoop(Loop *L, LoopInfo *LI,
return CurAST;
}
std::unique_ptr<AliasSetTracker>
LoopInvariantCodeMotion::collectAliasInfoForLoopWithMSSA(
Loop *L, AAResults *AA, MemorySSAUpdater *MSSAU) {
auto *MSSA = MSSAU->getMemorySSA();
auto CurAST = std::make_unique<AliasSetTracker>(*AA, MSSA, L);
CurAST->addAllInstructionsInLoopUsingMSSA();
return CurAST;
}
static bool pointerInvalidatedByLoop(MemoryLocation MemLoc,
AliasSetTracker *CurAST, Loop *CurLoop,
AAResults *AA) {