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[LICM] Use ICFLoopSafetyInfo in LICM

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This patch makes LICM use `ICFLoopSafetyInfo` that is a smarter version
of LoopSafetyInfo that leverages power of Implicit Control Flow Tracking
to keep track of throwing instructions and give less pessimistic answers
to queries related to throws.

The ICFLoopSafetyInfo itself has been introduced in rL344601. This patch
enables it in LICM only.

Differential Revision: https://reviews.llvm.org/D50377
Reviewed By: apilipenko

llvm-svn: 346201
This commit is contained in:
Max Kazantsev 2018-11-06 02:44:49 +00:00
parent 1d195ba0ad
commit 86590965e8
7 changed files with 240 additions and 33 deletions
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7
include/llvm/Transforms/Utils/LoopUtils.h
View File

@ -109,7 +109,7 @@ bool formLCSSARecursively(Loop &L, DominatorTree &DT, LoopInfo *LI,
/// arguments. Diagnostics is emitted via \p ORE. It returns changed status.
bool sinkRegion(DomTreeNode *, AliasAnalysis *, LoopInfo *, DominatorTree *,
TargetLibraryInfo *, TargetTransformInfo *, Loop *,
AliasSetTracker *, LoopSafetyInfo *,
AliasSetTracker *, ICFLoopSafetyInfo *,
OptimizationRemarkEmitter *ORE);
/// Walk the specified region of the CFG (defined by all blocks
@ -122,7 +122,7 @@ bool sinkRegion(DomTreeNode *, AliasAnalysis *, LoopInfo *, DominatorTree *,
/// ORE. It returns changed status.
bool hoistRegion(DomTreeNode *, AliasAnalysis *, LoopInfo *, DominatorTree *,
TargetLibraryInfo *, Loop *, AliasSetTracker *,
LoopSafetyInfo *, OptimizationRemarkEmitter *ORE);
ICFLoopSafetyInfo *, OptimizationRemarkEmitter *ORE);
/// This function deletes dead loops. The caller of this function needs to
/// guarantee that the loop is infact dead.
@ -151,7 +151,8 @@ bool promoteLoopAccessesToScalars(const SmallSetVector<Value *, 8> &,
SmallVectorImpl<Instruction *> &,
PredIteratorCache &, LoopInfo *,
DominatorTree *, const TargetLibraryInfo *,
Loop *, AliasSetTracker *, LoopSafetyInfo *,
Loop *, AliasSetTracker *,
ICFLoopSafetyInfo *,
OptimizationRemarkEmitter *);
/// Does a BFS from a given node to all of its children inside a given loop.

53
lib/Transforms/Scalar/LICM.cpp
View File

@ -103,10 +103,10 @@ static bool isNotUsedOrFreeInLoop(const Instruction &I, const Loop *CurLoop,
const LoopSafetyInfo *SafetyInfo,
TargetTransformInfo *TTI, bool &FreeInLoop);
static void hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
LoopSafetyInfo *SafetyInfo,
ICFLoopSafetyInfo *SafetyInfo,
OptimizationRemarkEmitter *ORE);
static bool sink(Instruction &I, LoopInfo *LI, DominatorTree *DT,
const Loop *CurLoop, LoopSafetyInfo *SafetyInfo,
const Loop *CurLoop, ICFLoopSafetyInfo *SafetyInfo,
OptimizationRemarkEmitter *ORE, bool FreeInLoop);
static bool isSafeToExecuteUnconditionally(Instruction &Inst,
const DominatorTree *DT,
@ -123,7 +123,8 @@ CloneInstructionInExitBlock(Instruction &I, BasicBlock &ExitBlock, PHINode &PN,
const LoopInfo *LI,
const LoopSafetyInfo *SafetyInfo);
static void eraseInstruction(Instruction &I, AliasSetTracker *AST);
static void eraseInstruction(Instruction &I, ICFLoopSafetyInfo &SafetyInfo,
AliasSetTracker *AST);
namespace {
struct LoopInvariantCodeMotion {
@ -269,7 +270,7 @@ bool LoopInvariantCodeMotion::runOnLoop(
BasicBlock *Preheader = L->getLoopPreheader();
// Compute loop safety information.
SimpleLoopSafetyInfo SafetyInfo;
ICFLoopSafetyInfo SafetyInfo(DT);
SafetyInfo.computeLoopSafetyInfo(L);
// We want to visit all of the instructions in this loop... that are not parts
@ -376,7 +377,7 @@ bool LoopInvariantCodeMotion::runOnLoop(
bool llvm::sinkRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
DominatorTree *DT, TargetLibraryInfo *TLI,
TargetTransformInfo *TTI, Loop *CurLoop,
AliasSetTracker *CurAST, LoopSafetyInfo *SafetyInfo,
AliasSetTracker *CurAST, ICFLoopSafetyInfo *SafetyInfo,
OptimizationRemarkEmitter *ORE) {
// Verify inputs.
@ -406,7 +407,7 @@ bool llvm::sinkRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
LLVM_DEBUG(dbgs() << "LICM deleting dead inst: " << I << '\n');
salvageDebugInfo(I);
++II;
eraseInstruction(I, CurAST);
eraseInstruction(I, *SafetyInfo, CurAST);
Changed = true;
continue;
}
@ -423,7 +424,7 @@ bool llvm::sinkRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
if (sink(I, LI, DT, CurLoop, SafetyInfo, ORE, FreeInLoop)) {
if (!FreeInLoop) {
++II;
eraseInstruction(I, CurAST);
eraseInstruction(I, *SafetyInfo, CurAST);
}
Changed = true;
}
@ -440,7 +441,7 @@ bool llvm::sinkRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
///
bool llvm::hoistRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
DominatorTree *DT, TargetLibraryInfo *TLI, Loop *CurLoop,
AliasSetTracker *CurAST, LoopSafetyInfo *SafetyInfo,
AliasSetTracker *CurAST, ICFLoopSafetyInfo *SafetyInfo,
OptimizationRemarkEmitter *ORE) {
// Verify inputs.
assert(N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr &&
@ -481,7 +482,7 @@ bool llvm::hoistRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
CurAST->copyValue(&I, C);
I.replaceAllUsesWith(C);
if (isInstructionTriviallyDead(&I, TLI))
eraseInstruction(I, CurAST);
eraseInstruction(I, *SafetyInfo, CurAST);
Changed = true;
continue;
}
@ -510,14 +511,16 @@ bool llvm::hoistRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
auto One = llvm::ConstantFP::get(Divisor->getType(), 1.0);
auto ReciprocalDivisor = BinaryOperator::CreateFDiv(One, Divisor);
ReciprocalDivisor->setFastMathFlags(I.getFastMathFlags());
SafetyInfo->insertInstructionTo(I.getParent());
ReciprocalDivisor->insertBefore(&I);
auto Product =
BinaryOperator::CreateFMul(I.getOperand(0), ReciprocalDivisor);
Product->setFastMathFlags(I.getFastMathFlags());
SafetyInfo->insertInstructionTo(I.getParent());
Product->insertAfter(&I);
I.replaceAllUsesWith(Product);
eraseInstruction(I, CurAST);
eraseInstruction(I, *SafetyInfo, CurAST);
hoist(*ReciprocalDivisor, DT, CurLoop, SafetyInfo, ORE);
Changed = true;
@ -886,9 +889,11 @@ CloneInstructionInExitBlock(Instruction &I, BasicBlock &ExitBlock, PHINode &PN,
return New;
}
static void eraseInstruction(Instruction &I, AliasSetTracker *AST) {
static void eraseInstruction(Instruction &I, ICFLoopSafetyInfo &SafetyInfo,
AliasSetTracker *AST) {
if (AST)
AST->deleteValue(&I);
SafetyInfo.removeInstruction(&I);
I.eraseFromParent();
}
@ -999,7 +1004,7 @@ static void splitPredecessorsOfLoopExit(PHINode *PN, DominatorTree *DT,
/// position, and may either delete it or move it to outside of the loop.
///
static bool sink(Instruction &I, LoopInfo *LI, DominatorTree *DT,
const Loop *CurLoop, LoopSafetyInfo *SafetyInfo,
const Loop *CurLoop, ICFLoopSafetyInfo *SafetyInfo,
OptimizationRemarkEmitter *ORE, bool FreeInLoop) {
LLVM_DEBUG(dbgs() << "LICM sinking instruction: " << I << "\n");
ORE->emit([&]() {
@ -1090,7 +1095,7 @@ static bool sink(Instruction &I, LoopInfo *LI, DominatorTree *DT,
Instruction *New = sinkThroughTriviallyReplaceablePHI(PN, &I, LI, SunkCopies,
SafetyInfo, CurLoop);
PN->replaceAllUsesWith(New);
eraseInstruction(*PN, nullptr);
eraseInstruction(*PN, *SafetyInfo, nullptr);
Changed = true;
}
return Changed;
@ -1100,7 +1105,7 @@ static bool sink(Instruction &I, LoopInfo *LI, DominatorTree *DT,
/// is safe to hoist, this instruction is called to do the dirty work.
///
static void hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
LoopSafetyInfo *SafetyInfo, OptimizationRemarkEmitter *ORE) {
ICFLoopSafetyInfo *SafetyInfo, OptimizationRemarkEmitter *ORE) {
auto *Preheader = CurLoop->getLoopPreheader();
LLVM_DEBUG(dbgs() << "LICM hoisting to " << Preheader->getName() << ": " << I
<< "\n");
@ -1120,6 +1125,8 @@ static void hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
!SafetyInfo->isGuaranteedToExecute(I, DT, CurLoop))
I.dropUnknownNonDebugMetadata();
SafetyInfo->removeInstruction(&I);
SafetyInfo->insertInstructionTo(Preheader);
// Move the new node to the Preheader, before its terminator.
I.moveBefore(Preheader->getTerminator());
@ -1180,6 +1187,7 @@ class LoopPromoter : public LoadAndStorePromoter {
int Alignment;
bool UnorderedAtomic;
AAMDNodes AATags;
ICFLoopSafetyInfo &SafetyInfo;
Value *maybeInsertLCSSAPHI(Value *V, BasicBlock *BB) const {
if (Instruction *I = dyn_cast<Instruction>(V))
@ -1202,11 +1210,13 @@ public:
SmallVectorImpl<BasicBlock *> &LEB,
SmallVectorImpl<Instruction *> &LIP, PredIteratorCache &PIC,
AliasSetTracker &ast, LoopInfo &li, DebugLoc dl, int alignment,
bool UnorderedAtomic, const AAMDNodes &AATags)
bool UnorderedAtomic, const AAMDNodes &AATags,
ICFLoopSafetyInfo &SafetyInfo)
: LoadAndStorePromoter(Insts, S), SomePtr(SP), PointerMustAliases(PMA),
LoopExitBlocks(LEB), LoopInsertPts(LIP), PredCache(PIC), AST(ast),
LI(li), DL(std::move(dl)), Alignment(alignment),
UnorderedAtomic(UnorderedAtomic), AATags(AATags) {}
UnorderedAtomic(UnorderedAtomic), AATags(AATags), SafetyInfo(SafetyInfo)
{}
bool isInstInList(Instruction *I,
const SmallVectorImpl<Instruction *> &) const override {
@ -1243,7 +1253,10 @@ public:
// Update alias analysis.
AST.copyValue(LI, V);
}
void instructionDeleted(Instruction *I) const override { AST.deleteValue(I); }
void instructionDeleted(Instruction *I) const override {
SafetyInfo.removeInstruction(I);
AST.deleteValue(I);
}
};
@ -1281,7 +1294,7 @@ bool llvm::promoteLoopAccessesToScalars(
SmallVectorImpl<BasicBlock *> &ExitBlocks,
SmallVectorImpl<Instruction *> &InsertPts, PredIteratorCache &PIC,
LoopInfo *LI, DominatorTree *DT, const TargetLibraryInfo *TLI,
Loop *CurLoop, AliasSetTracker *CurAST, LoopSafetyInfo *SafetyInfo,
Loop *CurLoop, AliasSetTracker *CurAST, ICFLoopSafetyInfo *SafetyInfo,
OptimizationRemarkEmitter *ORE) {
// Verify inputs.
assert(LI != nullptr && DT != nullptr && CurLoop != nullptr &&
@ -1500,7 +1513,7 @@ bool llvm::promoteLoopAccessesToScalars(
SSAUpdater SSA(&NewPHIs);
LoopPromoter Promoter(SomePtr, LoopUses, SSA, PointerMustAliases, ExitBlocks,
InsertPts, PIC, *CurAST, *LI, DL, Alignment,
SawUnorderedAtomic, AATags);
SawUnorderedAtomic, AATags, *SafetyInfo);
// Set up the preheader to have a definition of the value. It is the live-out
// value from the preheader that uses in the loop will use.
@ -1520,7 +1533,7 @@ bool llvm::promoteLoopAccessesToScalars(
// If the SSAUpdater didn't use the load in the preheader, just zap it now.
if (PreheaderLoad->use_empty())
eraseInstruction(*PreheaderLoad, CurAST);
eraseInstruction(*PreheaderLoad, *SafetyInfo, CurAST);
return true;
}

2
test/CodeGen/AMDGPU/build-vector-insert-elt-infloop.ll
View File

@ -18,7 +18,7 @@ bb1:
%tmp4 = bitcast half %tmp3 to i16
%tmp5 = insertelement <2 x i16> <i16 0, i16 undef>, i16 %tmp4, i32 1
%tmp6 = bitcast i16* %arg to half*
store half %tmp2, half* %tmp6, align 2
store volatile half %tmp2, half* %tmp6, align 2
%tmp7 = bitcast <2 x i16> %tmp to <2 x half>
%tmp8 = extractelement <2 x half> %tmp7, i32 0
br label %bb1

6
test/Transforms/LICM/guards.ll
View File

@ -85,15 +85,15 @@ loop:
}
; TODO: We can also hoist this load and guard from mustexec non-header block.
; TODO: We can also hoist this guard from mustexec non-header block.
define void @test4(i1 %c, i32* %p) {
; CHECK-LABEL: @test4(
; CHECK-LABEL: entry:
; CHECK-LABEL: loop:
; CHECK-LABEL: backedge:
; CHECK: %a = load i32, i32* %p
; CHECK: %invariant_cond = icmp ne i32 %a, 100
; CHECK-LABEL: loop:
; CHECK-LABEL: backedge:
; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 %invariant_cond)
entry:

147
test/Transforms/LICM/hoist-mustexec.ll
View File

@ -456,3 +456,150 @@ backedge:
exit:
ret void
}
; Check that we can hoist a mustexecute load from backedge even if something
; throws after it.
define void @test_hoist_from_backedge_01(i32* %p, i32 %n) {
; CHECK-LABEL: @test_hoist_from_backedge_01(
; CHECK: entry:
; CHECK-NEXT: %load = load i32, i32* %p
; CHECK-NOT: load i32
entry:
br label %loop
loop:
%iv = phi i32 [ 0, %entry ], [ %iv.next, %backedge ]
%dummy = phi i32 [ 0, %entry ], [ %merge, %backedge ]
%cond = icmp slt i32 %iv, %n
br i1 %cond, label %if.true, label %if.false
if.true:
%a = add i32 %iv, %iv
br label %backedge
if.false:
%b = mul i32 %iv, %iv
br label %backedge
backedge:
%merge = phi i32 [ %a, %if.true ], [ %b, %if.false ]
%iv.next = add i32 %iv, %merge
%load = load i32, i32* %p
call void @may_throw()
%loop.cond = icmp ult i32 %iv.next, %load
br i1 %loop.cond, label %loop, label %exit
exit:
ret void
}
; Check that we don't hoist the load if something before it can throw.
define void @test_hoist_from_backedge_02(i32* %p, i32 %n) {
; CHECK-LABEL: @test_hoist_from_backedge_02(
; CHECK: entry:
; CHECK: loop:
; CHECK: %load = load i32, i32* %p
entry:
br label %loop
loop:
%iv = phi i32 [ 0, %entry ], [ %iv.next, %backedge ]
%dummy = phi i32 [ 0, %entry ], [ %merge, %backedge ]
%cond = icmp slt i32 %iv, %n
br i1 %cond, label %if.true, label %if.false
if.true:
%a = add i32 %iv, %iv
br label %backedge
if.false:
%b = mul i32 %iv, %iv
br label %backedge
backedge:
%merge = phi i32 [ %a, %if.true ], [ %b, %if.false ]
%iv.next = add i32 %iv, %merge
call void @may_throw()
%load = load i32, i32* %p
%loop.cond = icmp ult i32 %iv.next, %load
br i1 %loop.cond, label %loop, label %exit
exit:
ret void
}
define void @test_hoist_from_backedge_03(i32* %p, i32 %n) {
; CHECK-LABEL: @test_hoist_from_backedge_03(
; CHECK: entry:
; CHECK: loop:
; CHECK: %load = load i32, i32* %p
entry:
br label %loop
loop:
%iv = phi i32 [ 0, %entry ], [ %iv.next, %backedge ]
%dummy = phi i32 [ 0, %entry ], [ %merge, %backedge ]
%cond = icmp slt i32 %iv, %n
br i1 %cond, label %if.true, label %if.false
if.true:
%a = add i32 %iv, %iv
br label %backedge
if.false:
%b = mul i32 %iv, %iv
call void @may_throw()
br label %backedge
backedge:
%merge = phi i32 [ %a, %if.true ], [ %b, %if.false ]
%iv.next = add i32 %iv, %merge
%load = load i32, i32* %p
%loop.cond = icmp ult i32 %iv.next, %load
br i1 %loop.cond, label %loop, label %exit
exit:
ret void
}
define void @test_hoist_from_backedge_04(i32* %p, i32 %n) {
; CHECK-LABEL: @test_hoist_from_backedge_04(
; CHECK: entry:
; CHECK: loop:
; CHECK: %load = load i32, i32* %p
entry:
br label %loop
loop:
%iv = phi i32 [ 0, %entry ], [ %iv.next, %backedge ]
%dummy = phi i32 [ 0, %entry ], [ %merge, %backedge ]
call void @may_throw()
%cond = icmp slt i32 %iv, %n
br i1 %cond, label %if.true, label %if.false
if.true:
%a = add i32 %iv, %iv
br label %backedge
if.false:
%b = mul i32 %iv, %iv
br label %backedge
backedge:
%merge = phi i32 [ %a, %if.true ], [ %b, %if.false ]
%iv.next = add i32 %iv, %merge
%load = load i32, i32* %p
%loop.cond = icmp ult i32 %iv.next, %load
br i1 %loop.cond, label %loop, label %exit
exit:
ret void
}

29
test/Transforms/LICM/hoist-nounwind.ll
View File

@ -49,14 +49,16 @@ for.cond.cleanup:
ret i32 0
}
; Don't hoist load past volatile load.
; Hoist a non-volatile load past volatile load.
define i32 @test3(i32* noalias nocapture readonly %a, i32* %v) nounwind uwtable {
; CHECK-LABEL: @test3(
entry:
br label %for.body
; CHECK: load i32
; CHECK: for.body:
; CHECK: load volatile i32
; CHECK-NEXT: load i32
; CHECK-NOT: load
for.body:
%i.06 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
%x.05 = phi i32 [ 0, %entry ], [ %add, %for.body ]
@ -70,3 +72,26 @@ for.body:
for.cond.cleanup:
ret i32 %add
}
; Don't a volatile load past volatile load.
define i32 @test4(i32* noalias nocapture readonly %a, i32* %v) nounwind uwtable {
; CHECK-LABEL: @test4(
entry:
br label %for.body
; CHECK: for.body:
; CHECK: load volatile i32
; CHECK-NEXT: load volatile i32
for.body:
%i.06 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
%x.05 = phi i32 [ 0, %entry ], [ %add, %for.body ]
%xxx = load volatile i32, i32* %v, align 4
%i1 = load volatile i32, i32* %a, align 4
%add = add nsw i32 %i1, %x.05
%inc = add nuw nsw i32 %i.06, 1
%exitcond = icmp eq i32 %inc, 1000
br i1 %exitcond, label %for.cond.cleanup, label %for.body
for.cond.cleanup:
ret i32 %add
}

29
test/Transforms/LICM/preheader-safe.ll
View File

@ -112,12 +112,13 @@ loop-if:
exit:
ret void
}
; Negative test - can't move out of throwing block
define void @nothrow_header_neg(i64 %x, i64 %y, i1 %cond) {
; CHECK-LABEL: nothrow_header_neg
; Positive test - can hoist something that happens before thrower.
define void @nothrow_header_pos(i64 %x, i64 %y, i1 %cond) {
; CHECK-LABEL: nothrow_header_pos
; CHECK-LABEL: entry
; CHECK-LABEL: loop
; CHECK: %div = udiv i64 %x, %y
; CHECK-LABEL: loop
; CHECK: call void @use(i64 %div)
entry:
br label %loop
@ -128,3 +129,23 @@ loop-if:
call void @use(i64 %div)
br label %loop
}
; Negative test - can't move out of throwing block
define void @nothrow_header_neg(i64 %x, i64 %y, i1 %cond) {
; CHECK-LABEL: nothrow_header_neg
; CHECK-LABEL: entry
; CHECK-LABEL: loop
; CHECK: call void @maythrow()
; CHECK: %div = udiv i64 %x, %y
; CHECK: call void @use(i64 %div)
entry:
br label %loop
loop: ; preds = %entry, %for.inc
br label %loop-if
loop-if:
call void @maythrow()
%div = udiv i64 %x, %y
call void @use(i64 %div)
br label %loop
}