[llvm-branch-commits] [llvm] [LLVM][Coroutines] Create `.noalloc` variant of switch ABI coroutine ramp functions during CoroSplit (PR #99283)
Yuxuan Chen via llvm-branch-commits
llvm-branch-commits at lists.llvm.org
Sun Sep 8 21:47:38 PDT 2024
https://github.com/yuxuanchen1997 updated https://github.com/llvm/llvm-project/pull/99283
>From 0c712a2fbc5b44e892b37085dbace8ba974c1238 Mon Sep 17 00:00:00 2001
From: Yuxuan Chen <yuxuanchen1997 at outlook.com>
Date: Tue, 4 Jun 2024 23:22:00 -0700
Subject: [PATCH] [LLVM][Coroutines] Create `.noalloc` variant of switch ABI
coroutine ramp functions during CoroSplit
---
llvm/docs/Coroutines.rst | 18 +++
llvm/lib/Transforms/Coroutines/CoroInternal.h | 7 +
llvm/lib/Transforms/Coroutines/CoroSplit.cpp | 150 +++++++++++++++---
llvm/lib/Transforms/Coroutines/Coroutines.cpp | 27 ++++
.../Transforms/Coroutines/coro-split-00.ll | 15 ++
5 files changed, 191 insertions(+), 26 deletions(-)
diff --git a/llvm/docs/Coroutines.rst b/llvm/docs/Coroutines.rst
index 36092325e536fb..5679aefcb421d8 100644
--- a/llvm/docs/Coroutines.rst
+++ b/llvm/docs/Coroutines.rst
@@ -2022,6 +2022,12 @@ The pass CoroSplit builds coroutine frame and outlines resume and destroy parts
into separate functions. This pass also lowers `coro.await.suspend.void`_,
`coro.await.suspend.bool`_ and `coro.await.suspend.handle`_ intrinsics.
+CoroAnnotationElide
+-------------------
+This pass finds all usages of coroutines that are "must elide" and replaces
+`coro.begin` intrinsic with an address of a coroutine frame placed on its caller
+and replaces `coro.alloc` and `coro.free` intrinsics with `false` and `null`
+respectively to remove the deallocation code.
CoroElide
---------
@@ -2049,6 +2055,18 @@ the coroutine must reach the final suspend point when it get destroyed.
This attribute only works for switched-resume coroutines now.
+coro_elide_safe
+---------------
+
+When a Call or Invoke instruction to switch ABI coroutine `f` is marked with
+`coro_elide_safe`, CoroSplitPass generates a `f.noalloc` ramp function.
+`f.noalloc` has one more argument than its original ramp function `f`, which is
+the pointer to the allocated frame. `f.noalloc` also suppressed any allocations
+or deallocations that may be guarded by `@llvm.coro.alloc` and `@llvm.coro.free`.
+
+CoroAnnotationElidePass performs the heap elision when possible. Note that for
+recursive or mutually recursive functions this elision is usually not possible.
+
Metadata
========
diff --git a/llvm/lib/Transforms/Coroutines/CoroInternal.h b/llvm/lib/Transforms/Coroutines/CoroInternal.h
index d535ad7f85d74a..be86f96525b677 100644
--- a/llvm/lib/Transforms/Coroutines/CoroInternal.h
+++ b/llvm/lib/Transforms/Coroutines/CoroInternal.h
@@ -26,6 +26,13 @@ bool declaresIntrinsics(const Module &M,
const std::initializer_list<StringRef>);
void replaceCoroFree(CoroIdInst *CoroId, bool Elide);
+/// Replaces all @llvm.coro.alloc intrinsics calls associated with a given
+/// call @llvm.coro.id instruction with boolean value false.
+void suppressCoroAllocs(CoroIdInst *CoroId);
+/// Replaces CoroAllocs with boolean value false.
+void suppressCoroAllocs(LLVMContext &Context,
+ ArrayRef<CoroAllocInst *> CoroAllocs);
+
/// Attempts to rewrite the location operand of debug intrinsics in terms of
/// the coroutine frame pointer, folding pointer offsets into the DIExpression
/// of the intrinsic.
diff --git a/llvm/lib/Transforms/Coroutines/CoroSplit.cpp b/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
index 6bf3c75b95113e..494c4d632de95f 100644
--- a/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
+++ b/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
@@ -25,6 +25,7 @@
#include "llvm/ADT/PriorityWorklist.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Analysis/CFG.h"
@@ -1177,6 +1178,14 @@ static void updateAsyncFuncPointerContextSize(coro::Shape &Shape) {
Shape.AsyncLowering.AsyncFuncPointer->setInitializer(NewFuncPtrStruct);
}
+static TypeSize getFrameSizeForShape(coro::Shape &Shape) {
+ // In the same function all coro.sizes should have the same result type.
+ auto *SizeIntrin = Shape.CoroSizes.back();
+ Module *M = SizeIntrin->getModule();
+ const DataLayout &DL = M->getDataLayout();
+ return DL.getTypeAllocSize(Shape.FrameTy);
+}
+
static void replaceFrameSizeAndAlignment(coro::Shape &Shape) {
if (Shape.ABI == coro::ABI::Async)
updateAsyncFuncPointerContextSize(Shape);
@@ -1192,10 +1201,8 @@ static void replaceFrameSizeAndAlignment(coro::Shape &Shape) {
// In the same function all coro.sizes should have the same result type.
auto *SizeIntrin = Shape.CoroSizes.back();
- Module *M = SizeIntrin->getModule();
- const DataLayout &DL = M->getDataLayout();
- auto Size = DL.getTypeAllocSize(Shape.FrameTy);
- auto *SizeConstant = ConstantInt::get(SizeIntrin->getType(), Size);
+ auto *SizeConstant =
+ ConstantInt::get(SizeIntrin->getType(), getFrameSizeForShape(Shape));
for (CoroSizeInst *CS : Shape.CoroSizes) {
CS->replaceAllUsesWith(SizeConstant);
@@ -1452,6 +1459,75 @@ struct SwitchCoroutineSplitter {
setCoroInfo(F, Shape, Clones);
}
+ // Create a variant of ramp function that does not perform heap allocation
+ // for a switch ABI coroutine.
+ //
+ // The newly split `.noalloc` ramp function has the following differences:
+ // - Has one additional frame pointer parameter in lieu of dynamic
+ // allocation.
+ // - Suppressed allocations by replacing coro.alloc and coro.free.
+ static Function *createNoAllocVariant(Function &F, coro::Shape &Shape,
+ SmallVectorImpl<Function *> &Clones) {
+ assert(Shape.ABI == coro::ABI::Switch);
+ auto *OrigFnTy = F.getFunctionType();
+ auto OldParams = OrigFnTy->params();
+
+ SmallVector<Type *> NewParams;
+ NewParams.reserve(OldParams.size() + 1);
+ NewParams.append(OldParams.begin(), OldParams.end());
+ NewParams.push_back(PointerType::getUnqual(Shape.FrameTy));
+
+ auto *NewFnTy = FunctionType::get(OrigFnTy->getReturnType(), NewParams,
+ OrigFnTy->isVarArg());
+ Function *NoAllocF =
+ Function::Create(NewFnTy, F.getLinkage(), F.getName() + ".noalloc");
+
+ ValueToValueMapTy VMap;
+ unsigned int Idx = 0;
+ for (const auto &I : F.args()) {
+ VMap[&I] = NoAllocF->getArg(Idx++);
+ }
+ // We just appended the frame pointer as the last argument of the new
+ // function.
+ auto FrameIdx = NoAllocF->arg_size() - 1;
+ SmallVector<ReturnInst *, 4> Returns;
+ CloneFunctionInto(NoAllocF, &F, VMap,
+ CloneFunctionChangeType::LocalChangesOnly, Returns);
+
+ if (Shape.CoroBegin) {
+ auto *NewCoroBegin =
+ cast_if_present<CoroBeginInst>(VMap[Shape.CoroBegin]);
+ auto *NewCoroId = cast<CoroIdInst>(NewCoroBegin->getId());
+ coro::replaceCoroFree(NewCoroId, /*Elide=*/true);
+ coro::suppressCoroAllocs(NewCoroId);
+ NewCoroBegin->replaceAllUsesWith(NoAllocF->getArg(FrameIdx));
+ NewCoroBegin->eraseFromParent();
+ }
+
+ Module *M = F.getParent();
+ M->getFunctionList().insert(M->end(), NoAllocF);
+
+ removeUnreachableBlocks(*NoAllocF);
+ auto NewAttrs = NoAllocF->getAttributes();
+ // When we elide allocation, we read these attributes to determine the
+ // frame size and alignment.
+ addFramePointerAttrs(NewAttrs, NoAllocF->getContext(), FrameIdx,
+ Shape.FrameSize, Shape.FrameAlign,
+ /*NoAlias=*/false);
+
+ NoAllocF->setAttributes(NewAttrs);
+
+ Clones.push_back(NoAllocF);
+ // Reset the original function's coro info, make the new noalloc variant
+ // connected to the original ramp function.
+ setCoroInfo(F, Shape, Clones);
+ // After copying, set the linkage to internal linkage. Original function
+ // may have different linkage, but optimization dependent on this function
+ // generally relies on LTO.
+ NoAllocF->setLinkage(llvm::GlobalValue::InternalLinkage);
+ return NoAllocF;
+ }
+
private:
// Create a resume clone by cloning the body of the original function, setting
// new entry block and replacing coro.suspend an appropriate value to force
@@ -1910,6 +1986,33 @@ class PrettyStackTraceFunction : public PrettyStackTraceEntry {
};
} // namespace
+/// Remove calls to llvm.coro.end in the original function.
+static void removeCoroEndsFromRampFunction(const coro::Shape &Shape) {
+ if (Shape.ABI != coro::ABI::Switch) {
+ for (auto *End : Shape.CoroEnds) {
+ replaceCoroEnd(End, Shape, Shape.FramePtr, /*in resume*/ false, nullptr);
+ }
+ } else {
+ for (llvm::AnyCoroEndInst *End : Shape.CoroEnds) {
+ auto &Context = End->getContext();
+ End->replaceAllUsesWith(ConstantInt::getFalse(Context));
+ End->eraseFromParent();
+ }
+ }
+}
+
+static bool hasSafeElideCaller(Function &F) {
+ for (auto *U : F.users()) {
+ if (auto *CB = dyn_cast<CallBase>(U)) {
+ auto *Caller = CB->getFunction();
+ if (Caller && Caller->isPresplitCoroutine() &&
+ CB->hasFnAttr(llvm::Attribute::CoroElideSafe))
+ return true;
+ }
+ }
+ return false;
+}
+
static coro::Shape
splitCoroutine(Function &F, SmallVectorImpl<Function *> &Clones,
TargetTransformInfo &TTI, bool OptimizeFrame,
@@ -1929,10 +2032,15 @@ splitCoroutine(Function &F, SmallVectorImpl<Function *> &Clones,
simplifySuspendPoints(Shape);
buildCoroutineFrame(F, Shape, TTI, MaterializableCallback);
replaceFrameSizeAndAlignment(Shape);
+ bool isNoSuspendCoroutine = Shape.CoroSuspends.empty();
+
+ bool shouldCreateNoAllocVariant = !isNoSuspendCoroutine &&
+ Shape.ABI == coro::ABI::Switch &&
+ hasSafeElideCaller(F);
// If there are no suspend points, no split required, just remove
// the allocation and deallocation blocks, they are not needed.
- if (Shape.CoroSuspends.empty()) {
+ if (isNoSuspendCoroutine) {
handleNoSuspendCoroutine(Shape);
} else {
switch (Shape.ABI) {
@@ -1962,22 +2070,13 @@ splitCoroutine(Function &F, SmallVectorImpl<Function *> &Clones,
coro::salvageDebugInfo(ArgToAllocaMap, *DDI, false /*UseEntryValue*/);
for (DbgVariableRecord *DVR : DbgVariableRecords)
coro::salvageDebugInfo(ArgToAllocaMap, *DVR, false /*UseEntryValue*/);
- return Shape;
-}
-/// Remove calls to llvm.coro.end in the original function.
-static void removeCoroEndsFromRampFunction(const coro::Shape &Shape) {
- if (Shape.ABI != coro::ABI::Switch) {
- for (auto *End : Shape.CoroEnds) {
- replaceCoroEnd(End, Shape, Shape.FramePtr, /*in resume*/ false, nullptr);
- }
- } else {
- for (llvm::AnyCoroEndInst *End : Shape.CoroEnds) {
- auto &Context = End->getContext();
- End->replaceAllUsesWith(ConstantInt::getFalse(Context));
- End->eraseFromParent();
- }
- }
+ removeCoroEndsFromRampFunction(Shape);
+
+ if (shouldCreateNoAllocVariant)
+ SwitchCoroutineSplitter::createNoAllocVariant(F, Shape, Clones);
+
+ return Shape;
}
static void updateCallGraphAfterCoroutineSplit(
@@ -2108,13 +2207,12 @@ PreservedAnalyses CoroSplitPass::run(LazyCallGraph::SCC &C,
F.setSplittedCoroutine();
SmallVector<Function *, 4> Clones;
- auto &ORE = FAM.getResult<OptimizationRemarkEmitterAnalysis>(F);
- const coro::Shape Shape =
+ coro::Shape Shape =
splitCoroutine(F, Clones, FAM.getResult<TargetIRAnalysis>(F),
OptimizeFrame, MaterializableCallback);
- removeCoroEndsFromRampFunction(Shape);
updateCallGraphAfterCoroutineSplit(*N, Shape, Clones, C, CG, AM, UR, FAM);
+ auto &ORE = FAM.getResult<OptimizationRemarkEmitterAnalysis>(F);
ORE.emit([&]() {
return OptimizationRemark(DEBUG_TYPE, "CoroSplit", &F)
<< "Split '" << ore::NV("function", F.getName())
@@ -2130,9 +2228,9 @@ PreservedAnalyses CoroSplitPass::run(LazyCallGraph::SCC &C,
}
}
- for (auto *PrepareFn : PrepareFns) {
- replaceAllPrepares(PrepareFn, CG, C);
- }
+ for (auto *PrepareFn : PrepareFns) {
+ replaceAllPrepares(PrepareFn, CG, C);
+ }
return PreservedAnalyses::none();
}
diff --git a/llvm/lib/Transforms/Coroutines/Coroutines.cpp b/llvm/lib/Transforms/Coroutines/Coroutines.cpp
index 1a92bc1636257b..be257339e0ac49 100644
--- a/llvm/lib/Transforms/Coroutines/Coroutines.cpp
+++ b/llvm/lib/Transforms/Coroutines/Coroutines.cpp
@@ -145,6 +145,33 @@ void coro::replaceCoroFree(CoroIdInst *CoroId, bool Elide) {
}
}
+void coro::suppressCoroAllocs(CoroIdInst *CoroId) {
+ SmallVector<CoroAllocInst *, 4> CoroAllocs;
+ for (User *U : CoroId->users())
+ if (auto *CA = dyn_cast<CoroAllocInst>(U))
+ CoroAllocs.push_back(CA);
+
+ if (CoroAllocs.empty())
+ return;
+
+ coro::suppressCoroAllocs(CoroId->getContext(), CoroAllocs);
+}
+
+// Replacing llvm.coro.alloc with false will suppress dynamic
+// allocation as it is expected for the frontend to generate the code that
+// looks like:
+// id = coro.id(...)
+// mem = coro.alloc(id) ? malloc(coro.size()) : 0;
+// coro.begin(id, mem)
+void coro::suppressCoroAllocs(LLVMContext &Context,
+ ArrayRef<CoroAllocInst *> CoroAllocs) {
+ auto *False = ConstantInt::getFalse(Context);
+ for (auto *CA : CoroAllocs) {
+ CA->replaceAllUsesWith(False);
+ CA->eraseFromParent();
+ }
+}
+
static void clear(coro::Shape &Shape) {
Shape.CoroBegin = nullptr;
Shape.CoroEnds.clear();
diff --git a/llvm/test/Transforms/Coroutines/coro-split-00.ll b/llvm/test/Transforms/Coroutines/coro-split-00.ll
index b35bd720b86f96..9909627e60597d 100644
--- a/llvm/test/Transforms/Coroutines/coro-split-00.ll
+++ b/llvm/test/Transforms/Coroutines/coro-split-00.ll
@@ -32,6 +32,13 @@ suspend:
ret ptr %hdl
}
+; Make a safe_elide call to f and CoroSplit should generate the .noalloc variant
+define void @caller() presplitcoroutine {
+entry:
+ %ptr = call ptr @f() #1
+ ret void
+}
+
; CHECK-LABEL: @f() !func_sanitize !0 {
; CHECK: call ptr @malloc
; CHECK: @llvm.coro.begin(token %id, ptr %phi)
@@ -63,6 +70,13 @@ suspend:
; CHECK-NOT: call void @free(
; CHECK: ret void
+; CHECK-LABEL: @f.noalloc(ptr noundef nonnull align 8 dereferenceable(24) %{{.*}})
+; CHECK-NOT: call ptr @malloc
+; CHECK: call void @print(i32 0)
+; CHECK-NOT: call void @print(i32 1)
+; CHECK-NOT: call void @free(
+; CHECK: ret ptr %{{.*}}
+
declare ptr @llvm.coro.free(token, ptr)
declare i32 @llvm.coro.size.i32()
declare i8 @llvm.coro.suspend(token, i1)
@@ -79,3 +93,4 @@ declare void @print(i32)
declare void @free(ptr) willreturn allockind("free") "alloc-family"="malloc"
!0 = !{i32 846595819, ptr null}
+attributes #1 = { coro_elide_safe }
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