[AA][MemCpyOpt] Introduce CapturesBeforeAnalysis and ChainedCaptureAnalysis (NFCI) #174739
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…alysis (NFCI) Following up on llvm#110484, it should be possible to drop `callCaptureBefore`, whose last user is MemCpyOpt, while retaining its additional precision by encapsulating it into a dedicated CapturesBeforeAnalysis. This uses `PointerMayBeCapturedBefore` and is more precise than EarliestEscapeAnalysis, though more expensive. Also allow users to query them in chain when needed.
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@llvm/pr-subscribers-llvm-analysis Author: Antonio Frighetto (antoniofrighetto) ChangesFollowing up on #110484, it should be possible to drop Full diff: https://github.com/llvm/llvm-project/pull/174739.diff 4 Files Affected:
diff --git a/llvm/include/llvm/Analysis/AliasAnalysis.h b/llvm/include/llvm/Analysis/AliasAnalysis.h
index 878b7e7a1fb3b..0bdfa797e670c 100644
--- a/llvm/include/llvm/Analysis/AliasAnalysis.h
+++ b/llvm/include/llvm/Analysis/AliasAnalysis.h
@@ -198,6 +198,37 @@ class LLVM_ABI EarliestEscapeAnalysis final : public CaptureAnalysis {
void removeInstruction(Instruction *I);
};
+/// Context-sensitive CaptureAnalysis provider, which precisely determines
+/// whether an object is captured before a specific instruction using
+/// PointerMayBeCapturedBefore.
+class LLVM_ABI CapturesBeforeAnalysis final : public CaptureAnalysis {
+ const DominatorTree &DT;
+ const LoopInfo *LI;
+
+public:
+ CapturesBeforeAnalysis(const DominatorTree &DT, const LoopInfo *LI = nullptr)
+ : DT(DT), LI(LI) {}
+
+ CaptureComponents getCapturesBefore(const Value *Object, const Instruction *I,
+ bool OrAt) override;
+};
+
+/// A CaptureAnalysis provider that chains EarliestEscapeAnalysis and
+/// CapturesBeforeAnalysis. It favours the former, cached but approximate;
+/// falling back to the latter, precise but expensive, when needed.
+class LLVM_ABI ChainedCaptureAnalysis final : public CaptureAnalysis {
+ EarliestEscapeAnalysis &EEA;
+ CapturesBeforeAnalysis &CBA;
+
+public:
+ ChainedCaptureAnalysis(EarliestEscapeAnalysis &EEA,
+ CapturesBeforeAnalysis &CBA)
+ : EEA(EEA), CBA(CBA) {}
+
+ CaptureComponents getCapturesBefore(const Value *Object, const Instruction *I,
+ bool OrAt) override;
+};
+
/// Cache key for BasicAA results. It only includes the pointer and size from
/// MemoryLocation, as BasicAA is AATags independent. Additionally, it includes
/// the value of MayBeCrossIteration, which may affect BasicAA results.
@@ -531,22 +562,6 @@ class AAResults {
LLVM_ABI ModRefInfo getModRefInfo(const Instruction *I1,
const Instruction *I2);
- /// Return information about whether a particular call site modifies
- /// or reads the specified memory location \p MemLoc before instruction \p I
- /// in a BasicBlock.
- ModRefInfo callCapturesBefore(const Instruction *I,
- const MemoryLocation &MemLoc,
- DominatorTree *DT) {
- SimpleAAQueryInfo AAQIP(*this);
- return callCapturesBefore(I, MemLoc, DT, AAQIP);
- }
-
- /// A convenience wrapper to synthesize a memory location.
- ModRefInfo callCapturesBefore(const Instruction *I, const Value *P,
- LocationSize Size, DominatorTree *DT) {
- return callCapturesBefore(I, MemoryLocation(P, Size), DT);
- }
-
/// @}
//===--------------------------------------------------------------------===//
/// \name Higher level methods for querying mod/ref information.
diff --git a/llvm/lib/Analysis/AliasAnalysis.cpp b/llvm/lib/Analysis/AliasAnalysis.cpp
index fd2f7c1ea9c8d..fd34204eff003 100644
--- a/llvm/lib/Analysis/AliasAnalysis.cpp
+++ b/llvm/lib/Analysis/AliasAnalysis.cpp
@@ -616,71 +616,6 @@ ModRefInfo AAResults::getModRefInfo(const Instruction *I,
}
}
-/// Return information about whether a particular call site modifies
-/// or reads the specified memory location \p MemLoc before instruction \p I
-/// in a BasicBlock.
-/// FIXME: this is really just shoring-up a deficiency in alias analysis.
-/// BasicAA isn't willing to spend linear time determining whether an alloca
-/// was captured before or after this particular call, while we are. However,
-/// with a smarter AA in place, this test is just wasting compile time.
-ModRefInfo AAResults::callCapturesBefore(const Instruction *I,
- const MemoryLocation &MemLoc,
- DominatorTree *DT,
- AAQueryInfo &AAQI) {
- if (!DT)
- return ModRefInfo::ModRef;
-
- const Value *Object = getUnderlyingObject(MemLoc.Ptr);
- if (!isIdentifiedFunctionLocal(Object))
- return ModRefInfo::ModRef;
-
- const auto *Call = dyn_cast<CallBase>(I);
- if (!Call || Call == Object)
- return ModRefInfo::ModRef;
-
- if (capturesAnything(PointerMayBeCapturedBefore(
- Object, /* ReturnCaptures */ true, I, DT,
- /* include Object */ true, CaptureComponents::Provenance)))
- return ModRefInfo::ModRef;
-
- unsigned ArgNo = 0;
- ModRefInfo R = ModRefInfo::NoModRef;
- // Set flag only if no May found and all operands processed.
- for (auto CI = Call->data_operands_begin(), CE = Call->data_operands_end();
- CI != CE; ++CI, ++ArgNo) {
- // Only look at the no-capture or byval pointer arguments. If this
- // pointer were passed to arguments that were neither of these, then it
- // couldn't be no-capture.
- if (!(*CI)->getType()->isPointerTy())
- continue;
-
- // Make sure we still check captures(ret: address, provenance) and
- // captures(address) arguments, as these wouldn't be treated as a capture
- // at the call-site.
- CaptureInfo Captures = Call->getCaptureInfo(ArgNo);
- if (capturesAnyProvenance(Captures.getOtherComponents()))
- continue;
-
- AliasResult AR =
- alias(MemoryLocation::getBeforeOrAfter(*CI),
- MemoryLocation::getBeforeOrAfter(Object), AAQI, Call);
- // If this is a no-capture pointer argument, see if we can tell that it
- // is impossible to alias the pointer we're checking. If not, we have to
- // assume that the call could touch the pointer, even though it doesn't
- // escape.
- if (AR == AliasResult::NoAlias)
- continue;
- if (Call->doesNotAccessMemory(ArgNo))
- continue;
- if (Call->onlyReadsMemory(ArgNo)) {
- R = ModRefInfo::Ref;
- continue;
- }
- return ModRefInfo::ModRef;
- }
- return R;
-}
-
/// canBasicBlockModify - Return true if it is possible for execution of the
/// specified basic block to modify the location Loc.
///
diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index 1d5f9ac465808..f085d720ba597 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -270,6 +270,32 @@ void EarliestEscapeAnalysis::removeInstruction(Instruction *I) {
}
}
+CaptureComponents
+CapturesBeforeAnalysis::getCapturesBefore(const Value *Object,
+ const Instruction *I, bool OrAt) {
+ assert(I && "CapturesBeforeAnalysis requires a context instruction.");
+ if (!isIdentifiedFunctionLocal(Object))
+ return CaptureComponents::Provenance;
+
+ return PointerMayBeCapturedBefore(
+ Object, /* ReturnCaptures */ true, I, &DT, /* IncludeI */ true,
+ CaptureComponents::Provenance, capturesAnything, LI);
+}
+
+CaptureComponents
+ChainedCaptureAnalysis::getCapturesBefore(const Value *Object,
+ const Instruction *I, bool OrAt) {
+ CaptureComponents CC = EEA.getCapturesBefore(Object, I, OrAt);
+ if (!capturesAnyProvenance(CC))
+ return CC;
+
+ // If we still happen not to have the context instruction, we cannot provide
+ // more precision than EarliestEscapeAnalysis.
+ if (!I)
+ return CC;
+ return CBA.getCapturesBefore(Object, I, OrAt);
+}
+
//===----------------------------------------------------------------------===//
// GetElementPtr Instruction Decomposition and Analysis
//===----------------------------------------------------------------------===//
diff --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index f054b21f2e9dd..5f0e90eed747f 100644
--- a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -1048,14 +1048,15 @@ bool MemCpyOptPass::performCallSlotOptzn(Instruction *cpyLoad,
// In addition to knowing that the call does not access src in some
// unexpected manner, for example via a global, which we deduce from
// the use analysis, we also need to know that it does not sneakily
- // access dest. We rely on AA to figure this out for us.
- MemoryLocation DestWithSrcSize(cpyDest, LocationSize::precise(srcSize));
- ModRefInfo MR = BAA.getModRefInfo(C, DestWithSrcSize);
- // If necessary, perform additional analysis.
- if (isModOrRefSet(MR))
- MR = BAA.callCapturesBefore(C, DestWithSrcSize, DT);
- if (isModOrRefSet(MR))
- return false;
+ // access dest. We rely on AA with CapturesBeforeAnalysis to figure this out.
+ {
+ MemoryLocation DestWithSrcSize(cpyDest, LocationSize::precise(srcSize));
+ CapturesBeforeAnalysis CBA(*DT);
+ ChainedCaptureAnalysis CCA(*EEA, CBA);
+ BatchAAResults BAAWithCCA(*AA, &CCA);
+ if (isModOrRefSet(BAAWithCCA.getModRefInfo(C, DestWithSrcSize)))
+ return false;
+ }
// We can't create address space casts here because we don't know if they're
// safe for the target.
|
Member
|
@llvm/pr-subscribers-llvm-transforms Author: Antonio Frighetto (antoniofrighetto) ChangesFollowing up on #110484, it should be possible to drop Full diff: https://github.com/llvm/llvm-project/pull/174739.diff 4 Files Affected:
diff --git a/llvm/include/llvm/Analysis/AliasAnalysis.h b/llvm/include/llvm/Analysis/AliasAnalysis.h
index 878b7e7a1fb3b..0bdfa797e670c 100644
--- a/llvm/include/llvm/Analysis/AliasAnalysis.h
+++ b/llvm/include/llvm/Analysis/AliasAnalysis.h
@@ -198,6 +198,37 @@ class LLVM_ABI EarliestEscapeAnalysis final : public CaptureAnalysis {
void removeInstruction(Instruction *I);
};
+/// Context-sensitive CaptureAnalysis provider, which precisely determines
+/// whether an object is captured before a specific instruction using
+/// PointerMayBeCapturedBefore.
+class LLVM_ABI CapturesBeforeAnalysis final : public CaptureAnalysis {
+ const DominatorTree &DT;
+ const LoopInfo *LI;
+
+public:
+ CapturesBeforeAnalysis(const DominatorTree &DT, const LoopInfo *LI = nullptr)
+ : DT(DT), LI(LI) {}
+
+ CaptureComponents getCapturesBefore(const Value *Object, const Instruction *I,
+ bool OrAt) override;
+};
+
+/// A CaptureAnalysis provider that chains EarliestEscapeAnalysis and
+/// CapturesBeforeAnalysis. It favours the former, cached but approximate;
+/// falling back to the latter, precise but expensive, when needed.
+class LLVM_ABI ChainedCaptureAnalysis final : public CaptureAnalysis {
+ EarliestEscapeAnalysis &EEA;
+ CapturesBeforeAnalysis &CBA;
+
+public:
+ ChainedCaptureAnalysis(EarliestEscapeAnalysis &EEA,
+ CapturesBeforeAnalysis &CBA)
+ : EEA(EEA), CBA(CBA) {}
+
+ CaptureComponents getCapturesBefore(const Value *Object, const Instruction *I,
+ bool OrAt) override;
+};
+
/// Cache key for BasicAA results. It only includes the pointer and size from
/// MemoryLocation, as BasicAA is AATags independent. Additionally, it includes
/// the value of MayBeCrossIteration, which may affect BasicAA results.
@@ -531,22 +562,6 @@ class AAResults {
LLVM_ABI ModRefInfo getModRefInfo(const Instruction *I1,
const Instruction *I2);
- /// Return information about whether a particular call site modifies
- /// or reads the specified memory location \p MemLoc before instruction \p I
- /// in a BasicBlock.
- ModRefInfo callCapturesBefore(const Instruction *I,
- const MemoryLocation &MemLoc,
- DominatorTree *DT) {
- SimpleAAQueryInfo AAQIP(*this);
- return callCapturesBefore(I, MemLoc, DT, AAQIP);
- }
-
- /// A convenience wrapper to synthesize a memory location.
- ModRefInfo callCapturesBefore(const Instruction *I, const Value *P,
- LocationSize Size, DominatorTree *DT) {
- return callCapturesBefore(I, MemoryLocation(P, Size), DT);
- }
-
/// @}
//===--------------------------------------------------------------------===//
/// \name Higher level methods for querying mod/ref information.
diff --git a/llvm/lib/Analysis/AliasAnalysis.cpp b/llvm/lib/Analysis/AliasAnalysis.cpp
index fd2f7c1ea9c8d..fd34204eff003 100644
--- a/llvm/lib/Analysis/AliasAnalysis.cpp
+++ b/llvm/lib/Analysis/AliasAnalysis.cpp
@@ -616,71 +616,6 @@ ModRefInfo AAResults::getModRefInfo(const Instruction *I,
}
}
-/// Return information about whether a particular call site modifies
-/// or reads the specified memory location \p MemLoc before instruction \p I
-/// in a BasicBlock.
-/// FIXME: this is really just shoring-up a deficiency in alias analysis.
-/// BasicAA isn't willing to spend linear time determining whether an alloca
-/// was captured before or after this particular call, while we are. However,
-/// with a smarter AA in place, this test is just wasting compile time.
-ModRefInfo AAResults::callCapturesBefore(const Instruction *I,
- const MemoryLocation &MemLoc,
- DominatorTree *DT,
- AAQueryInfo &AAQI) {
- if (!DT)
- return ModRefInfo::ModRef;
-
- const Value *Object = getUnderlyingObject(MemLoc.Ptr);
- if (!isIdentifiedFunctionLocal(Object))
- return ModRefInfo::ModRef;
-
- const auto *Call = dyn_cast<CallBase>(I);
- if (!Call || Call == Object)
- return ModRefInfo::ModRef;
-
- if (capturesAnything(PointerMayBeCapturedBefore(
- Object, /* ReturnCaptures */ true, I, DT,
- /* include Object */ true, CaptureComponents::Provenance)))
- return ModRefInfo::ModRef;
-
- unsigned ArgNo = 0;
- ModRefInfo R = ModRefInfo::NoModRef;
- // Set flag only if no May found and all operands processed.
- for (auto CI = Call->data_operands_begin(), CE = Call->data_operands_end();
- CI != CE; ++CI, ++ArgNo) {
- // Only look at the no-capture or byval pointer arguments. If this
- // pointer were passed to arguments that were neither of these, then it
- // couldn't be no-capture.
- if (!(*CI)->getType()->isPointerTy())
- continue;
-
- // Make sure we still check captures(ret: address, provenance) and
- // captures(address) arguments, as these wouldn't be treated as a capture
- // at the call-site.
- CaptureInfo Captures = Call->getCaptureInfo(ArgNo);
- if (capturesAnyProvenance(Captures.getOtherComponents()))
- continue;
-
- AliasResult AR =
- alias(MemoryLocation::getBeforeOrAfter(*CI),
- MemoryLocation::getBeforeOrAfter(Object), AAQI, Call);
- // If this is a no-capture pointer argument, see if we can tell that it
- // is impossible to alias the pointer we're checking. If not, we have to
- // assume that the call could touch the pointer, even though it doesn't
- // escape.
- if (AR == AliasResult::NoAlias)
- continue;
- if (Call->doesNotAccessMemory(ArgNo))
- continue;
- if (Call->onlyReadsMemory(ArgNo)) {
- R = ModRefInfo::Ref;
- continue;
- }
- return ModRefInfo::ModRef;
- }
- return R;
-}
-
/// canBasicBlockModify - Return true if it is possible for execution of the
/// specified basic block to modify the location Loc.
///
diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index 1d5f9ac465808..f085d720ba597 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -270,6 +270,32 @@ void EarliestEscapeAnalysis::removeInstruction(Instruction *I) {
}
}
+CaptureComponents
+CapturesBeforeAnalysis::getCapturesBefore(const Value *Object,
+ const Instruction *I, bool OrAt) {
+ assert(I && "CapturesBeforeAnalysis requires a context instruction.");
+ if (!isIdentifiedFunctionLocal(Object))
+ return CaptureComponents::Provenance;
+
+ return PointerMayBeCapturedBefore(
+ Object, /* ReturnCaptures */ true, I, &DT, /* IncludeI */ true,
+ CaptureComponents::Provenance, capturesAnything, LI);
+}
+
+CaptureComponents
+ChainedCaptureAnalysis::getCapturesBefore(const Value *Object,
+ const Instruction *I, bool OrAt) {
+ CaptureComponents CC = EEA.getCapturesBefore(Object, I, OrAt);
+ if (!capturesAnyProvenance(CC))
+ return CC;
+
+ // If we still happen not to have the context instruction, we cannot provide
+ // more precision than EarliestEscapeAnalysis.
+ if (!I)
+ return CC;
+ return CBA.getCapturesBefore(Object, I, OrAt);
+}
+
//===----------------------------------------------------------------------===//
// GetElementPtr Instruction Decomposition and Analysis
//===----------------------------------------------------------------------===//
diff --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index f054b21f2e9dd..5f0e90eed747f 100644
--- a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -1048,14 +1048,15 @@ bool MemCpyOptPass::performCallSlotOptzn(Instruction *cpyLoad,
// In addition to knowing that the call does not access src in some
// unexpected manner, for example via a global, which we deduce from
// the use analysis, we also need to know that it does not sneakily
- // access dest. We rely on AA to figure this out for us.
- MemoryLocation DestWithSrcSize(cpyDest, LocationSize::precise(srcSize));
- ModRefInfo MR = BAA.getModRefInfo(C, DestWithSrcSize);
- // If necessary, perform additional analysis.
- if (isModOrRefSet(MR))
- MR = BAA.callCapturesBefore(C, DestWithSrcSize, DT);
- if (isModOrRefSet(MR))
- return false;
+ // access dest. We rely on AA with CapturesBeforeAnalysis to figure this out.
+ {
+ MemoryLocation DestWithSrcSize(cpyDest, LocationSize::precise(srcSize));
+ CapturesBeforeAnalysis CBA(*DT);
+ ChainedCaptureAnalysis CCA(*EEA, CBA);
+ BatchAAResults BAAWithCCA(*AA, &CCA);
+ if (isModOrRefSet(BAAWithCCA.getModRefInfo(C, DestWithSrcSize)))
+ return false;
+ }
// We can't create address space casts here because we don't know if they're
// safe for the target.
|
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Kind ping on direction. |
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Following up on #110484, it should be possible to drop
callCaptureBefore, whose last user is MemCpyOpt, while retaining its additional precision by encapsulating it into a dedicated CapturesBeforeAnalysis. This usesPointerMayBeCapturedBeforeand is more precise than EarliestEscapeAnalysis, though more expensive. Also allow users to query them in chain when needed.