[llvm-commits] [llvm] r143630 - in /llvm/trunk: lib/Transforms/Scalar/DeadStoreElimination.cpp test/Transforms/DeadStoreElimination/OverwriteStoreEnd.ll
Peter Cooper
peter_cooper at apple.com
Fri Nov 4 09:27:51 PDT 2011
Hi Eli
Thanks for letting me know. I'll revert it now until i've fixed the problems.
Pete
On Nov 3, 2011, at 3:09 PM, Eli Friedman wrote:
> On Thu, Nov 3, 2011 at 11:01 AM, Pete Cooper <peter_cooper at apple.com> wrote:
>> Author: pete
>> Date: Thu Nov 3 13:01:56 2011
>> New Revision: 143630
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=143630&view=rev
>> Log:
>> DeadStoreElimination can now trim the size of a store if the end of it is dead.
>>
>> Only currently done if the later store is writing to a power of 2 address or
>> has the same alignment as the earlier store as then its likely to not break up
>> large stores into smaller ones
>>
>> Fixes <rdar://problem/10140300>
>
> This appears to be causing a bunch of failures on buildbots; please
> fix or revert.
>
> -Eli
>
>> Added:
>> llvm/trunk/test/Transforms/DeadStoreElimination/OverwriteStoreEnd.ll
>> Modified:
>> llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp
>>
>> Modified: llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp?rev=143630&r1=143629&r2=143630&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp (original)
>> +++ llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp Thu Nov 3 13:01:56 2011
>> @@ -239,6 +239,24 @@
>> }
>> }
>>
>> +
>> +/// isShortenable - Returns true if this instruction can be safely shortened in
>> +/// length.
>> +static bool isShortenable(Instruction *I) {
>> + // Don't shorten stores for now
>> + if (isa<StoreInst>(I))
>> + return false;
>> +
>> + IntrinsicInst *II = cast<IntrinsicInst>(I);
>> + switch (II->getIntrinsicID()) {
>> + default: return false;
>> + case Intrinsic::memset:
>> + case Intrinsic::memcpy:
>> + // Do shorten memory intrinsics.
>> + return true;
>> + }
>> +}
>> +
>> /// getStoredPointerOperand - Return the pointer that is being written to.
>> static Value *getStoredPointerOperand(Instruction *I) {
>> if (StoreInst *SI = dyn_cast<StoreInst>(I))
>> @@ -293,11 +311,24 @@
>> return false;
>> }
>>
>> -/// isCompleteOverwrite - Return true if a store to the 'Later' location
>> +namespace {
>> + enum OverwriteResult
>> + {
>> + OverwriteComplete,
>> + OverwriteEnd,
>> + OverwriteUnknown
>> + };
>> +}
>> +
>> +/// isOverwrite - Return 'OverwriteComplete' if a store to the 'Later' location
>> /// completely overwrites a store to the 'Earlier' location.
>> -static bool isCompleteOverwrite(const AliasAnalysis::Location &Later,
>> - const AliasAnalysis::Location &Earlier,
>> - AliasAnalysis &AA) {
>> +/// 'OverwriteEnd' if the end of the 'Earlier' location is completely
>> +/// overwritten by 'Later', or 'OverwriteUnknown' if nothing can be determined
>> +static OverwriteResult isOverwrite(const AliasAnalysis::Location &Later,
>> + const AliasAnalysis::Location &Earlier,
>> + AliasAnalysis &AA,
>> + int64_t& EarlierOff,
>> + int64_t& LaterOff) {
>> const Value *P1 = Earlier.Ptr->stripPointerCasts();
>> const Value *P2 = Later.Ptr->stripPointerCasts();
>>
>> @@ -311,23 +342,24 @@
>> // If we have no TargetData information around, then the size of the store
>> // is inferrable from the pointee type. If they are the same type, then
>> // we know that the store is safe.
>> - if (AA.getTargetData() == 0)
>> - return Later.Ptr->getType() == Earlier.Ptr->getType();
>> - return false;
>> + if (AA.getTargetData() == 0 &&
>> + Later.Ptr->getType() == Earlier.Ptr->getType())
>> + return OverwriteComplete;
>> +
>> + return OverwriteUnknown;
>> }
>>
>> // Make sure that the Later size is >= the Earlier size.
>> - if (Later.Size < Earlier.Size)
>> - return false;
>> - return true;
>> + if (Later.Size >= Earlier.Size)
>> + return OverwriteComplete;
>> }
>>
>> // Otherwise, we have to have size information, and the later store has to be
>> // larger than the earlier one.
>> if (Later.Size == AliasAnalysis::UnknownSize ||
>> Earlier.Size == AliasAnalysis::UnknownSize ||
>> - Later.Size <= Earlier.Size || AA.getTargetData() == 0)
>> - return false;
>> + AA.getTargetData() == 0)
>> + return OverwriteUnknown;
>>
>> // Check to see if the later store is to the entire object (either a global,
>> // an alloca, or a byval argument). If so, then it clearly overwrites any
>> @@ -340,26 +372,27 @@
>> // If we can't resolve the same pointers to the same object, then we can't
>> // analyze them at all.
>> if (UO1 != UO2)
>> - return false;
>> + return OverwriteUnknown;
>>
>> // If the "Later" store is to a recognizable object, get its size.
>> if (isObjectPointerWithTrustworthySize(UO2)) {
>> uint64_t ObjectSize =
>> TD.getTypeAllocSize(cast<PointerType>(UO2->getType())->getElementType());
>> if (ObjectSize == Later.Size)
>> - return true;
>> + return OverwriteComplete;
>> }
>>
>> // Okay, we have stores to two completely different pointers. Try to
>> // decompose the pointer into a "base + constant_offset" form. If the base
>> // pointers are equal, then we can reason about the two stores.
>> - int64_t EarlierOff = 0, LaterOff = 0;
>> + EarlierOff = 0;
>> + LaterOff = 0;
>> const Value *BP1 = GetPointerBaseWithConstantOffset(P1, EarlierOff, TD);
>> const Value *BP2 = GetPointerBaseWithConstantOffset(P2, LaterOff, TD);
>>
>> // If the base pointers still differ, we have two completely different stores.
>> if (BP1 != BP2)
>> - return false;
>> + return OverwriteUnknown;
>>
>> // The later store completely overlaps the earlier store if:
>> //
>> @@ -377,11 +410,24 @@
>> //
>> // We have to be careful here as *Off is signed while *.Size is unsigned.
>> if (EarlierOff >= LaterOff &&
>> + Later.Size > Earlier.Size &&
>> uint64_t(EarlierOff - LaterOff) + Earlier.Size <= Later.Size)
>> - return true;
>> + return OverwriteComplete;
>> +
>> + // The other interesting case is if the later store overwrites the end of
>> + // the earlier store
>> + //
>> + // |--earlier--|
>> + // |-- later --|
>> + //
>> + // In this case we may want to trim the size of earlier to avoid generating
>> + // writes to addresses which will definitely be overwritten later
>> + if (LaterOff > EarlierOff &&
>> + LaterOff + Later.Size >= EarlierOff + Earlier.Size)
>> + return OverwriteEnd;
>>
>> // Otherwise, they don't completely overlap.
>> - return false;
>> + return OverwriteUnknown;
>> }
>>
>> /// isPossibleSelfRead - If 'Inst' might be a self read (i.e. a noop copy of a
>> @@ -505,22 +551,52 @@
>> // If we find a write that is a) removable (i.e., non-volatile), b) is
>> // completely obliterated by the store to 'Loc', and c) which we know that
>> // 'Inst' doesn't load from, then we can remove it.
>> - if (isRemovable(DepWrite) && isCompleteOverwrite(Loc, DepLoc, *AA) &&
>> + if (isRemovable(DepWrite) &&
>> !isPossibleSelfRead(Inst, Loc, DepWrite, *AA)) {
>> - DEBUG(dbgs() << "DSE: Remove Dead Store:\n DEAD: "
>> - << *DepWrite << "\n KILLER: " << *Inst << '\n');
>> -
>> - // Delete the store and now-dead instructions that feed it.
>> - DeleteDeadInstruction(DepWrite, *MD);
>> - ++NumFastStores;
>> - MadeChange = true;
>> + int64_t InstWriteOffset, DepWriteOffset;
>> + OverwriteResult OR = isOverwrite(Loc, DepLoc, *AA,
>> + DepWriteOffset, InstWriteOffset);
>> + if (OR == OverwriteComplete) {
>> + DEBUG(dbgs() << "DSE: Remove Dead Store:\n DEAD: "
>> + << *DepWrite << "\n KILLER: " << *Inst << '\n');
>>
>> - // DeleteDeadInstruction can delete the current instruction in loop
>> - // cases, reset BBI.
>> - BBI = Inst;
>> - if (BBI != BB.begin())
>> - --BBI;
>> - break;
>> + // Delete the store and now-dead instructions that feed it.
>> + DeleteDeadInstruction(DepWrite, *MD);
>> + ++NumFastStores;
>> + MadeChange = true;
>> +
>> + // DeleteDeadInstruction can delete the current instruction in loop
>> + // cases, reset BBI.
>> + BBI = Inst;
>> + if (BBI != BB.begin())
>> + --BBI;
>> + break;
>> + } else if (OR == OverwriteEnd && isShortenable(DepWrite)) {
>> + // TODO: base this on the target vector size so that if the earlier
>> + // store was too small to get vector writes anyway then its likely
>> + // a good idea to shorten it
>> + // Power of 2 vector writes are probably always a bad idea to optimize
>> + // as any store/memset/memcpy is likely using vector instructions so
>> + // shortening it to not vector size is likely to be slower
>> + MemIntrinsic* DepIntrinsic = cast<MemIntrinsic>(DepWrite);
>> + unsigned DepWriteAlign = DepIntrinsic->getAlignment();
>> + if (llvm::isPowerOf2_64(InstWriteOffset) ||
>> + ((DepWriteAlign != 0) && InstWriteOffset % DepWriteAlign == 0)) {
>> +
>> + DEBUG(dbgs() << "DSE: Remove Dead Store:\n OW END: "
>> + << *DepWrite << "\n KILLER (offset "
>> + << InstWriteOffset << ", "
>> + << DepLoc.Size << ")"
>> + << *Inst << '\n');
>> +
>> + Value* DepWriteLength = DepIntrinsic->getLength();
>> + Value* TrimmedLength = ConstantInt::get(DepWriteLength->getType(),
>> + InstWriteOffset -
>> + DepWriteOffset);
>> + DepIntrinsic->setLength(TrimmedLength);
>> + MadeChange = true;
>> + }
>> + }
>> }
>>
>> // If this is a may-aliased store that is clobbering the store value, we
>>
>> Added: llvm/trunk/test/Transforms/DeadStoreElimination/OverwriteStoreEnd.ll
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/DeadStoreElimination/OverwriteStoreEnd.ll?rev=143630&view=auto
>> ==============================================================================
>> --- llvm/trunk/test/Transforms/DeadStoreElimination/OverwriteStoreEnd.ll (added)
>> +++ llvm/trunk/test/Transforms/DeadStoreElimination/OverwriteStoreEnd.ll Thu Nov 3 13:01:56 2011
>> @@ -0,0 +1,78 @@
>> +; RUN: opt < %s -basicaa -dse -S | FileCheck %s
>> +target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
>> +
>> +%struct.vec2 = type { <4 x i32>, <4 x i32> }
>> +%struct.vec2plusi = type { <4 x i32>, <4 x i32>, i32 }
>> +
>> + at glob1 = global %struct.vec2 zeroinitializer, align 16
>> + at glob2 = global %struct.vec2plusi zeroinitializer, align 16
>> +
>> +define void @write24to28(i32* nocapture %p) nounwind uwtable ssp {
>> +; CHECK: @write24to28
>> +entry:
>> + %arrayidx0 = getelementptr inbounds i32* %p, i64 1
>> + %p3 = bitcast i32* %arrayidx0 to i8*
>> +; CHECK: call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 24, i32 4, i1 false)
>> + call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 28, i32 4, i1 false)
>> + %arrayidx1 = getelementptr inbounds i32* %p, i64 7
>> + store i32 1, i32* %arrayidx1, align 4
>> + ret void
>> +}
>> +
>> +define void @write28to32(i32* nocapture %p) nounwind uwtable ssp {
>> +; CHECK: @write28to32
>> +entry:
>> + %p3 = bitcast i32* %p to i8*
>> +; CHECK: call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 28, i32 4, i1 false)
>> + call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 32, i32 4, i1 false)
>> + %arrayidx1 = getelementptr inbounds i32* %p, i64 7
>> + store i32 1, i32* %arrayidx1, align 4
>> + ret void
>> +}
>> +
>> +define void @dontwrite28to32memset(i32* nocapture %p) nounwind uwtable ssp {
>> +; CHECK: @dontwrite28to32memset
>> +entry:
>> + %p3 = bitcast i32* %p to i8*
>> +; CHECK: call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 32, i32 16, i1 false)
>> + call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 32, i32 16, i1 false)
>> + %arrayidx1 = getelementptr inbounds i32* %p, i64 7
>> + store i32 1, i32* %arrayidx1, align 4
>> + ret void
>> +}
>> +
>> +define void @write32to36(%struct.vec2plusi* nocapture %p) nounwind uwtable ssp {
>> +; CHECK: @write32to36
>> +entry:
>> + %0 = bitcast %struct.vec2plusi* %p to i8*
>> +; CHECK: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %0, i8* bitcast (%struct.vec2plusi* @glob2 to i8*), i64 32, i32 16, i1 false)
>> + tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %0, i8* bitcast (%struct.vec2plusi* @glob2 to i8*), i64 36, i32 16, i1 false)
>> + %c = getelementptr inbounds %struct.vec2plusi* %p, i64 0, i32 2
>> + store i32 1, i32* %c, align 4
>> + ret void
>> +}
>> +
>> +define void @write16to32(%struct.vec2* nocapture %p) nounwind uwtable ssp {
>> +; CHECK: @write16to32
>> +entry:
>> + %0 = bitcast %struct.vec2* %p to i8*
>> +; CHECK: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %0, i8* bitcast (%struct.vec2* @glob1 to i8*), i64 16, i32 16, i1 false)
>> + tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %0, i8* bitcast (%struct.vec2* @glob1 to i8*), i64 32, i32 16, i1 false)
>> + %c = getelementptr inbounds %struct.vec2* %p, i64 0, i32 1
>> + store <4 x i32> <i32 1, i32 2, i32 3, i32 4>, <4 x i32>* %c, align 4
>> + ret void
>> +}
>> +
>> +define void @dontwrite28to32memcpy(%struct.vec2* nocapture %p) nounwind uwtable ssp {
>> +; CHECK: @dontwrite28to32memcpy
>> +entry:
>> + %0 = bitcast %struct.vec2* %p to i8*
>> +; CHECK: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %0, i8* bitcast (%struct.vec2* @glob1 to i8*), i64 32, i32 16, i1 false)
>> + tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %0, i8* bitcast (%struct.vec2* @glob1 to i8*), i64 32, i32 16, i1 false)
>> + %arrayidx1 = getelementptr inbounds %struct.vec2* %p, i64 0, i32 0, i64 7
>> + store i32 1, i32* %arrayidx1, align 4
>> + ret void
>> +}
>> +
>> +declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture, i64, i32, i1) nounwind
>> +declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1) nounwind
>>
>>
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