[LICM] Cap the clobbering calls in LICM.
Summary:
Unlimitted number of calls to getClobberingAccess can lead to high
compile times in pathological cases.
Switching EnableLicmCap flag from bool to int, and enabling to default 100.
(tested to be appropriate for current bechmarks)
We can revisit this value when enabling MemorySSA.
Reviewers: sanjoy, chandlerc, george.burgess.iv
Subscribers: jlebar, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D57968
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@353897 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/llvm/Transforms/Utils/LoopUtils.h b/include/llvm/Transforms/Utils/LoopUtils.h
index d144887..a5883ac 100644
--- a/include/llvm/Transforms/Utils/LoopUtils.h
+++ b/include/llvm/Transforms/Utils/LoopUtils.h
@@ -112,7 +112,7 @@
bool sinkRegion(DomTreeNode *, AliasAnalysis *, LoopInfo *, DominatorTree *,
TargetLibraryInfo *, TargetTransformInfo *, Loop *,
AliasSetTracker *, MemorySSAUpdater *, ICFLoopSafetyInfo *,
- bool, OptimizationRemarkEmitter *);
+ bool, int &, OptimizationRemarkEmitter *);
/// Walk the specified region of the CFG (defined by all blocks
/// dominated by the specified block, and that are in the current loop) in depth
@@ -124,7 +124,7 @@
/// ORE. It returns changed status.
bool hoistRegion(DomTreeNode *, AliasAnalysis *, LoopInfo *, DominatorTree *,
TargetLibraryInfo *, Loop *, AliasSetTracker *,
- MemorySSAUpdater *, ICFLoopSafetyInfo *, bool,
+ MemorySSAUpdater *, ICFLoopSafetyInfo *, bool, int &,
OptimizationRemarkEmitter *);
/// This function deletes dead loops. The caller of this function needs to
@@ -277,6 +277,7 @@
Loop *CurLoop, AliasSetTracker *CurAST,
MemorySSAUpdater *MSSAU, bool TargetExecutesOncePerLoop,
bool NoOfMemAccessesTooLarge,
+ int *LicmMssaOptCap = nullptr,
OptimizationRemarkEmitter *ORE = nullptr);
/// Returns a Min/Max operation corresponding to MinMaxRecurrenceKind.
diff --git a/lib/Transforms/Scalar/LICM.cpp b/lib/Transforms/Scalar/LICM.cpp
index c838897..7384ea0 100644
--- a/lib/Transforms/Scalar/LICM.cpp
+++ b/lib/Transforms/Scalar/LICM.cpp
@@ -106,17 +106,19 @@
LICMN2Theshold("licm-n2-threshold", cl::Hidden, cl::init(0),
cl::desc("How many instruction to cross product using AA"));
-// Experimental option to allow imprecision in LICM (use MemorySSA cap) in
-// pathological cases, in exchange for faster compile. This is to be removed
-// if MemorySSA starts to address the same issue. This flag applies only when
-// LICM uses MemorySSA instead on AliasSetTracker. When the flag is disabled
-// (default), LICM calls MemorySSAWalker's getClobberingMemoryAccess, which
-// gets perfect accuracy. When flag is enabled, LICM will call into MemorySSA's
-// getDefiningAccess, which may not be precise, since optimizeUses is capped.
-static cl::opt<bool> EnableLicmCap(
- "enable-licm-cap", cl::init(false), cl::Hidden,
- cl::desc("Enable imprecision in LICM (uses MemorySSA cap) in "
- "pathological cases, in exchange for faster compile"));
+// Experimental option to allow imprecision in LICM in pathological cases, in
+// exchange for faster compile. This is to be removed if MemorySSA starts to
+// address the same issue. This flag applies only when LICM uses MemorySSA
+// instead on AliasSetTracker. LICM calls MemorySSAWalker's
+// getClobberingMemoryAccess, up to the value of the Cap, getting perfect
+// accuracy. Afterwards, LICM will call into MemorySSA's getDefiningAccess,
+// which may not be precise, since optimizeUses is capped. The result is
+// correct, but we may not get as "far up" as possible to get which access is
+// clobbering the one queried.
+static cl::opt<int> LicmMssaOptCap(
+ "licm-mssa-optimization-cap", cl::init(100), cl::Hidden,
+ cl::desc("Enable imprecision in LICM in pathological cases, in exchange "
+ "for faster compile. Caps the MemorySSA clobbering calls."));
// Experimentally, memory promotion carries less importance than sinking and
// hoisting. Limit when we do promotion when using MemorySSA, in order to save
@@ -149,7 +151,8 @@
AliasSetTracker *CurAST, Loop *CurLoop,
AliasAnalysis *AA);
static bool pointerInvalidatedByLoopWithMSSA(MemorySSA *MSSA, MemoryUse *MU,
- Loop *CurLoop);
+ Loop *CurLoop,
+ int &LicmMssaOptCounter);
static Instruction *CloneInstructionInExitBlock(
Instruction &I, BasicBlock &ExitBlock, PHINode &PN, const LoopInfo *LI,
const LoopSafetyInfo *SafetyInfo, MemorySSAUpdater *MSSAU);
@@ -307,6 +310,7 @@
std::unique_ptr<AliasSetTracker> CurAST;
std::unique_ptr<MemorySSAUpdater> MSSAU;
bool NoOfMemAccTooLarge = false;
+ int LicmMssaOptCounter = 0;
if (!MSSA) {
LLVM_DEBUG(dbgs() << "LICM: Using Alias Set Tracker.\n");
@@ -352,11 +356,11 @@
if (L->hasDedicatedExits())
Changed |= sinkRegion(DT->getNode(L->getHeader()), AA, LI, DT, TLI, TTI, L,
CurAST.get(), MSSAU.get(), &SafetyInfo,
- NoOfMemAccTooLarge, ORE);
+ NoOfMemAccTooLarge, LicmMssaOptCounter, ORE);
if (Preheader)
Changed |= hoistRegion(DT->getNode(L->getHeader()), AA, LI, DT, TLI, L,
CurAST.get(), MSSAU.get(), &SafetyInfo,
- NoOfMemAccTooLarge, ORE);
+ NoOfMemAccTooLarge, LicmMssaOptCounter, ORE);
// Now that all loop invariants have been removed from the loop, promote any
// memory references to scalars that we can.
@@ -461,7 +465,7 @@
TargetTransformInfo *TTI, Loop *CurLoop,
AliasSetTracker *CurAST, MemorySSAUpdater *MSSAU,
ICFLoopSafetyInfo *SafetyInfo, bool NoOfMemAccTooLarge,
- OptimizationRemarkEmitter *ORE) {
+ int &LicmMssaOptCounter, OptimizationRemarkEmitter *ORE) {
// Verify inputs.
assert(N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr &&
@@ -505,7 +509,7 @@
bool FreeInLoop = false;
if (isNotUsedOrFreeInLoop(I, CurLoop, SafetyInfo, TTI, FreeInLoop) &&
canSinkOrHoistInst(I, AA, DT, CurLoop, CurAST, MSSAU, true,
- NoOfMemAccTooLarge, ORE) &&
+ NoOfMemAccTooLarge, &LicmMssaOptCounter, ORE) &&
!I.mayHaveSideEffects()) {
if (sink(I, LI, DT, CurLoop, SafetyInfo, MSSAU, ORE, FreeInLoop)) {
if (!FreeInLoop) {
@@ -760,6 +764,7 @@
DominatorTree *DT, TargetLibraryInfo *TLI, Loop *CurLoop,
AliasSetTracker *CurAST, MemorySSAUpdater *MSSAU,
ICFLoopSafetyInfo *SafetyInfo, bool NoOfMemAccTooLarge,
+ int &LicmMssaOptCounter,
OptimizationRemarkEmitter *ORE) {
// Verify inputs.
assert(N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr &&
@@ -813,7 +818,7 @@
// to that block.
if (CurLoop->hasLoopInvariantOperands(&I) &&
canSinkOrHoistInst(I, AA, DT, CurLoop, CurAST, MSSAU, true,
- NoOfMemAccTooLarge, ORE) &&
+ NoOfMemAccTooLarge, &LicmMssaOptCounter, ORE) &&
isSafeToExecuteUnconditionally(
I, DT, CurLoop, SafetyInfo, ORE,
CurLoop->getLoopPreheader()->getTerminator())) {
@@ -1040,13 +1045,15 @@
Loop *CurLoop, AliasSetTracker *CurAST,
MemorySSAUpdater *MSSAU,
bool TargetExecutesOncePerLoop,
- bool NoOfMemAccTooLarge,
+ bool NoOfMemAccTooLarge, int *LicmMssaOptCounter,
OptimizationRemarkEmitter *ORE) {
// If we don't understand the instruction, bail early.
if (!isHoistableAndSinkableInst(I))
return false;
MemorySSA *MSSA = MSSAU ? MSSAU->getMemorySSA() : nullptr;
+ if (MSSA)
+ assert(LicmMssaOptCounter != nullptr && "Counter cannot be null.");
// Loads have extra constraints we have to verify before we can hoist them.
if (LoadInst *LI = dyn_cast<LoadInst>(&I)) {
@@ -1073,7 +1080,8 @@
CurLoop, AA);
else
Invalidated = pointerInvalidatedByLoopWithMSSA(
- MSSA, cast<MemoryUse>(MSSA->getMemoryAccess(LI)), CurLoop);
+ MSSA, cast<MemoryUse>(MSSA->getMemoryAccess(LI)), CurLoop,
+ *LicmMssaOptCounter);
// Check loop-invariant address because this may also be a sinkable load
// whose address is not necessarily loop-invariant.
if (ORE && Invalidated && CurLoop->isLoopInvariant(LI->getPointerOperand()))
@@ -1118,7 +1126,8 @@
CurAST, CurLoop, AA);
else
Invalidated = pointerInvalidatedByLoopWithMSSA(
- MSSA, cast<MemoryUse>(MSSA->getMemoryAccess(CI)), CurLoop);
+ MSSA, cast<MemoryUse>(MSSA->getMemoryAccess(CI)), CurLoop,
+ *LicmMssaOptCounter);
if (Invalidated)
return false;
}
@@ -1177,8 +1186,9 @@
} else { // MSSAU
if (isOnlyMemoryAccess(SI, CurLoop, MSSAU))
return true;
- if (!EnableLicmCap) {
+ if (*LicmMssaOptCounter < LicmMssaOptCap) {
auto *Source = MSSA->getSkipSelfWalker()->getClobberingMemoryAccess(SI);
+ (*LicmMssaOptCounter)++;
// If there are no clobbering Defs in the loop, we still need to check
// for interfering Uses. If there are more accesses than the Promotion
// cap, give up, we're not walking a list that long. Otherwise, walk the
@@ -2195,13 +2205,16 @@
}
static bool pointerInvalidatedByLoopWithMSSA(MemorySSA *MSSA, MemoryUse *MU,
- Loop *CurLoop) {
+ Loop *CurLoop,
+ int &LicmMssaOptCounter) {
MemoryAccess *Source;
- // See declaration of EnableLicmCap for usage details.
- if (EnableLicmCap)
+ // See declaration of LicmMssaOptCap for usage details.
+ if (LicmMssaOptCounter >= LicmMssaOptCap)
Source = MU->getDefiningAccess();
- else
+ else {
Source = MSSA->getSkipSelfWalker()->getClobberingMemoryAccess(MU);
+ LicmMssaOptCounter++;
+ }
return !MSSA->isLiveOnEntryDef(Source) &&
CurLoop->contains(Source->getBlock());
}
