[llvm-commits] [llvm] r143630 - in /llvm/trunk: lib/Transforms/Scalar/DeadStoreElimination.cpp test/Transforms/DeadStoreElimination/OverwriteStoreEnd.ll
Eli Friedman
eli.friedman at gmail.com
Thu Nov 3 15:09:10 PDT 2011
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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