lxfind updated this revision to Diff 273173.
lxfind added a comment.
Remove unused variable
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D82314/new/
https://reviews.llvm.org/D82314
Files:
llvm/lib/Transforms/Coroutines/CoroSplit.cpp
llvm/test/Transforms/Coroutines/coro-split-02.ll
llvm/test/Transforms/Coroutines/coro-split-sink-lifetime.ll
Index: llvm/test/Transforms/Coroutines/coro-split-sink-lifetime.ll
===================================================================
--- llvm/test/Transforms/Coroutines/coro-split-sink-lifetime.ll
+++ llvm/test/Transforms/Coroutines/coro-split-sink-lifetime.ll
@@ -1,6 +1,5 @@
-; Tests that coro-split can handle the case when a code after coro.suspend uses
-; a value produces between coro.save and coro.suspend (%Result.i19)
-; and checks whether stray coro.saves are properly removed
+; Tests that coro-split will optimize the lifetime.start maker of each local variable,
+; sink them to the places closest to the actual use.
; RUN: opt < %s -coro-split -S | FileCheck %s
; RUN: opt < %s -passes=coro-split -S | FileCheck %s
@@ -15,6 +14,9 @@
entry:
%ref.tmp7 = alloca %"struct.lean_future<int>::Awaiter", align 8
%testval = alloca i32
+ %cast = bitcast i32* %testval to i8*
+ ; lifetime of %testval starts here, but not used until await.ready.
+ call void @llvm.lifetime.start.p0i8(i64 4, i8* %cast)
%id = call token @llvm.coro.id(i32 0, i8* null, i8* null, i8* null)
%alloc = call i8* @malloc(i64 16) #3
%vFrame = call noalias nonnull i8* @llvm.coro.begin(token %id, i8* %alloc)
@@ -29,8 +31,8 @@
await.ready:
%StrayCoroSave = call token @llvm.coro.save(i8* null)
%val = load i32, i32* %Result.i19
- %cast = bitcast i32* %testval to i8*
- call void @llvm.lifetime.start.p0i8(i64 4, i8* %cast)
+ %test = load i32, i32* %testval
+ call void @print(i32 %test)
call void @llvm.lifetime.end.p0i8(i64 4, i8* %cast)
call void @print(i32 %val)
br label %exit
@@ -40,14 +42,15 @@
}
; CHECK-LABEL: @a.resume(
-; CHECK: %testval = alloca i32
-; CHECK: getelementptr inbounds %a.Frame
+; CHECK: %testval = alloca i32, align 4
+; CHECK-NEXT: getelementptr inbounds %a.Frame
; CHECK-NEXT: getelementptr inbounds %"struct.lean_future<int>::Awaiter"
-; CHECK-NOT: call token @llvm.coro.save(i8* null)
+; CHECK-NEXT: %cast1 = bitcast i32* %testval to i8*
; CHECK-NEXT: %val = load i32, i32* %Result
-; CHECK-NEXT: %cast = bitcast i32* %testval to i8*
-; CHECK-NEXT: call void @llvm.lifetime.start.p0i8(i64 4, i8* %cast)
-; CHECK-NEXT: call void @llvm.lifetime.end.p0i8(i64 4, i8* %cast)
+; CHECK-NEXT: call void @llvm.lifetime.start.p0i8(i64 4, i8* %cast1)
+; CHECK-NEXT: %test = load i32, i32* %testval
+; CHECK-NEXT: call void @print(i32 %test)
+; CHECK-NEXT: call void @llvm.lifetime.end.p0i8(i64 4, i8* %cast1)
; CHECK-NEXT: call void @print(i32 %val)
; CHECK-NEXT: ret void
Index: llvm/test/Transforms/Coroutines/coro-split-02.ll
===================================================================
--- llvm/test/Transforms/Coroutines/coro-split-02.ll
+++ llvm/test/Transforms/Coroutines/coro-split-02.ll
@@ -31,6 +31,8 @@
%val = load i32, i32* %Result.i19
%cast = bitcast i32* %testval to i8*
call void @llvm.lifetime.start.p0i8(i64 4, i8* %cast)
+ %test = load i32, i32* %testval
+ call void @print(i32 %test)
call void @llvm.lifetime.end.p0i8(i64 4, i8* %cast)
call void @print(i32 %val)
br label %exit
@@ -47,6 +49,8 @@
; CHECK-NEXT: %val = load i32, i32* %Result
; CHECK-NEXT: %cast = bitcast i32* %testval to i8*
; CHECK-NEXT: call void @llvm.lifetime.start.p0i8(i64 4, i8* %cast)
+; CHECK-NEXT: %test = load i32, i32* %testval
+; CHECK-NEXT: call void @print(i32 %test)
; CHECK-NEXT: call void @llvm.lifetime.end.p0i8(i64 4, i8* %cast)
; CHECK-NEXT: call void @print(i32 %val)
; CHECK-NEXT: ret void
Index: llvm/lib/Transforms/Coroutines/CoroSplit.cpp
===================================================================
--- llvm/lib/Transforms/Coroutines/CoroSplit.cpp
+++ llvm/lib/Transforms/Coroutines/CoroSplit.cpp
@@ -75,7 +75,7 @@
namespace {
-/// A little helper class for building
+/// A little helper class for building
class CoroCloner {
public:
enum class Kind {
@@ -563,7 +563,7 @@
// In the original function, the AllocaSpillBlock is a block immediately
// following the allocation of the frame object which defines GEPs for
// all the allocas that have been moved into the frame, and it ends by
- // branching to the original beginning of the coroutine. Make this
+ // branching to the original beginning of the coroutine. Make this
// the entry block of the cloned function.
auto *Entry = cast<BasicBlock>(VMap[Shape.AllocaSpillBlock]);
auto *OldEntry = &NewF->getEntryBlock();
@@ -1239,6 +1239,103 @@
S.resize(N);
}
+/// For every local variable that has lifetime intrinsics markers, we sink
+/// their lifetime.start marker to the places where the variable is being
+/// used for the first time. Doing so minimizes the lifetime of each variable,
+/// hence minimizing the amount of data we end up putting on the frame.
+static void sinkLifetimeStartMarkers(Function &F) {
+ DominatorTree Dom(F);
+ for (Instruction &I : instructions(F)) {
+ // We look for this particular pattern:
+ // %tmpX = alloca %.., align ...
+ // %0 = bitcast %...* %tmpX to i8*
+ // call void @llvm.lifetime.start.p0i8(i64 ..., i8* nonnull %0) #2
+ if (!isa<AllocaInst>(&I))
+ continue;
+ // There can be multiple lifetime start markers for the same variable.
+ SmallPtrSet<IntrinsicInst *, 1> LifetimeStartInsts;
+ // SinkBarriers stores all instructions that use this local variable.
+ // When sinking the lifetime start intrinsics, we can never sink past
+ // these barriers.
+ SmallPtrSet<Instruction *, 4> SinkBarriers;
+ bool Valid = true;
+ auto AddSinkBarrier = [&](Instruction *I) {
+ // When adding a new barrier to SinkBarriers, we maintain the case
+ // that no instruction in SinkBarriers dominates another instruction.
+ SmallPtrSet<Instruction *, 1> ToRemove;
+ bool ShouldAdd = true;
+ for (auto *S : SinkBarriers) {
+ if (I == S || Dom.dominates(S, I)) {
+ ShouldAdd = false;
+ break;
+ } else if (Dom.dominates(I, S)) {
+ ToRemove.insert(S);
+ }
+ }
+ if (ShouldAdd) {
+ SinkBarriers.insert(I);
+ for (auto *R : ToRemove) {
+ SinkBarriers.erase(R);
+ }
+ }
+ };
+ for (User *U : I.users()) {
+ if (!isa<BitCastInst>(U))
+ continue;
+ for (User *CU : U->users()) {
+ // If we see any user of CastInst that's not lifetime start/end
+ // intrinsics, give up because it's too complex.
+ if (auto *CUI = dyn_cast<IntrinsicInst>(CU)) {
+ if (CUI->getIntrinsicID() == Intrinsic::lifetime_start)
+ LifetimeStartInsts.insert(CUI);
+ else if (CUI->getIntrinsicID() == Intrinsic::lifetime_end)
+ AddSinkBarrier(CUI);
+ else
+ Valid = false;
+ } else {
+ Valid = false;
+ }
+ }
+ }
+ if (!Valid || LifetimeStartInsts.empty())
+ continue;
+
+ for (User *U : I.users()) {
+ if (isa<BitCastInst>(U))
+ continue;
+ // Every user of the variable is also a sink barrier.
+ AddSinkBarrier(cast<Instruction>(U));
+ }
+
+ // For each sink barrier, we insert a lifetime start marker right
+ // before it.
+ for (auto *S : SinkBarriers) {
+ if (auto *IS = dyn_cast<IntrinsicInst>(S)) {
+ if (IS->getIntrinsicID() == Intrinsic::lifetime_end) {
+ // If we have a lifetime end marker in SinkBarriers, meaning it's
+ // not dominated by any other users, we can safely delete it.
+ IS->eraseFromParent();
+ continue;
+ }
+ }
+ // We find an existing lifetime.start marker that domintes the barrier,
+ // clone it and insert it right before the barrier. We cannot clone an
+ // arbitrary lifetime.start marker because we want to make sure the
+ // BitCast instruction referred in the marker also dominates the barrier.
+ for (const auto *LifetimeStart : LifetimeStartInsts) {
+ if (Dom.dominates(LifetimeStart, S)) {
+ LifetimeStart->clone()->insertBefore(S);
+ break;
+ }
+ }
+ }
+ // All the old lifetime.start markers are no longer necessary.
+ for (auto *S : LifetimeStartInsts) {
+ S->eraseFromParent();
+ }
+ }
+}
+
static void splitSwitchCoroutine(Function &F, coro::Shape &Shape,
SmallVectorImpl<Function *> &Clones) {
assert(Shape.ABI == coro::ABI::Switch);
@@ -1428,6 +1525,7 @@
return Shape;
simplifySuspendPoints(Shape);
+ sinkLifetimeStartMarkers(F);
buildCoroutineFrame(F, Shape);
replaceFrameSize(Shape);
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