[llvm-commits] [llvm] r151620 - in /llvm/trunk: lib/Transforms/Scalar/DeadStoreElimination.cpp test/Transforms/DeadStoreElimination/OverwriteStoreStart.ll
Pete Cooper
peter_cooper at apple.com
Mon Feb 27 20:27:10 PST 2012
Author: pete
Date: Mon Feb 27 22:27:10 2012
New Revision: 151620
URL: http://llvm.org/viewvc/llvm-project?rev=151620&view=rev
Log:
DSE: Shorten memset when a later store overwrites the start of it
Added:
llvm/trunk/test/Transforms/DeadStoreElimination/OverwriteStoreStart.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=151620&r1=151619&r2=151620&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp Mon Feb 27 22:27:10 2012
@@ -259,6 +259,13 @@
}
}
+
+/// isMemset - Returns true if this instruction is an intrinsic memset
+static bool isMemset(Instruction *I) {
+ IntrinsicInst *II = dyn_cast<IntrinsicInst>(I);
+ return II && II->getIntrinsicID() == Intrinsic::memset;
+}
+
/// getStoredPointerOperand - Return the pointer that is being written to.
static Value *getStoredPointerOperand(Instruction *I) {
if (StoreInst *SI = dyn_cast<StoreInst>(I))
@@ -310,14 +317,17 @@
{
OverwriteComplete,
OverwriteEnd,
+ OverwriteStart,
OverwriteUnknown
};
}
/// isOverwrite - Return 'OverwriteComplete' if a store to the 'Later' location
/// completely overwrites a store to the 'Earlier' location.
-/// 'OverwriteEnd' if the end of the 'Earlier' location is completely
-/// overwritten by 'Later', or 'OverwriteUnknown' if nothing can be determined
+/// 'OverwriteEnd' if the end of the 'Earlier' location is completely
+/// overwritten by 'Later', 'OverWriteStart' if the start of 'Earlier'
+/// 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,
@@ -418,6 +428,21 @@
LaterOff < int64_t(EarlierOff + Earlier.Size) &&
int64_t(LaterOff + Later.Size) >= int64_t(EarlierOff + Earlier.Size))
return OverwriteEnd;
+
+ // 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 (EarlierOff >= LaterOff &&
+ EarlierOff < int64_t(LaterOff + Later.Size) &&
+ int64_t(EarlierOff + Earlier.Size) >= int64_t(LaterOff + Later.Size)) {
+ LaterOff = LaterOff + Later.Size;
+ return OverwriteStart;
+ }
// Otherwise, they don't completely overlap.
return OverwriteUnknown;
@@ -589,6 +614,45 @@
DepIntrinsic->setLength(TrimmedLength);
MadeChange = true;
}
+ } else if (OR == OverwriteStart && isMemset(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
+ // TODO: shorten memcpy and memmove by offsetting the source address.
+ 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 START: "
+ << *DepWrite << "\n KILLER (offset "
+ << InstWriteOffset << ", "
+ << DepWriteOffset << ", "
+ << DepLoc.Size << ")"
+ << *Inst << '\n');
+
+ Value* DepWriteLength = DepIntrinsic->getLength();
+ Value* TrimmedLength = ConstantInt::get(DepWriteLength->getType(),
+ DepLoc.Size -
+ (InstWriteOffset -
+ DepWriteOffset));
+ DepIntrinsic->setLength(TrimmedLength);
+ const TargetData *TD = AA->getTargetData();
+ Type *IntPtrTy = TD->getIntPtrType(BB.getContext());
+ Value* Offset = ConstantInt::get(IntPtrTy,
+ InstWriteOffset - DepWriteOffset);
+ // Offset the start of the memset with a GEP. As the memset type is
+ // i8* a GEP will do this without needing to use ptrtoint, etc.
+ Value *Dest = GetElementPtrInst::Create(DepIntrinsic->getRawDest(),
+ Offset,
+ "",
+ DepWrite);
+ DepIntrinsic->setDest(Dest);
+ MadeChange = true;
+ }
}
}
Added: llvm/trunk/test/Transforms/DeadStoreElimination/OverwriteStoreStart.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/DeadStoreElimination/OverwriteStoreStart.ll?rev=151620&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/DeadStoreElimination/OverwriteStoreStart.ll (added)
+++ llvm/trunk/test/Transforms/DeadStoreElimination/OverwriteStoreStart.ll Mon Feb 27 22:27:10 2012
@@ -0,0 +1,71 @@
+; 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 @write4to8(i32* nocapture %p) nounwind uwtable ssp {
+; CHECK: @write4to8
+entry:
+ %arrayidx0 = getelementptr inbounds i32* %p, i64 1
+ %p3 = bitcast i32* %arrayidx0 to i8*
+; CHECK: call void @llvm.memset.p0i8.i64(i8* %{{[0-9]+}}, 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 1
+ store i32 1, i32* %arrayidx1, align 4
+ ret void
+}
+
+define void @write4to12(i32* nocapture %p) nounwind uwtable ssp {
+; CHECK: @write4to12
+entry:
+%arrayidx0 = getelementptr inbounds i32* %p, i64 1
+%p3 = bitcast i32* %arrayidx0 to i8*
+; CHECK: call void @llvm.memset.p0i8.i64(i8* %{{[0-9]+}}, i8 0, i64 20, i32 4, i1 false)
+call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 28, i32 4, i1 false)
+%arrayidx1 = bitcast i32* %arrayidx0 to i64*
+store i64 1, i64* %arrayidx1, align 4
+ret void
+}
+
+define void @write4to8_2(i32* nocapture %p) nounwind uwtable ssp {
+; CHECK: @write4to8_2
+entry:
+%arrayidx0 = getelementptr inbounds i32* %p, i64 1
+%p3 = bitcast i32* %arrayidx0 to i8*
+; CHECK: call void @llvm.memset.p0i8.i64(i8* %{{[0-9]+}}, 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 = bitcast i32* %p to i64*
+store i64 1, i64* %arrayidx1, align 4
+ret void
+}
+
+define void @dontwrite4to6(i32* nocapture %p) nounwind uwtable ssp {
+; CHECK: @dontwrite4to6
+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 28, i32 4, i1 false)
+call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 28, i32 4, i1 false)
+%arrayidx1 = bitcast i32* %arrayidx0 to i16*
+store i16 1, i16* %arrayidx1, align 4
+ret void
+}
+
+define void @write4to8_neg_gep(i32* nocapture %p) nounwind uwtable ssp {
+; CHECK: @write4to8_neg_gep
+entry:
+%arrayidx0 = getelementptr inbounds i32* %p, i64 -1
+%p3 = bitcast i32* %arrayidx0 to i8*
+; CHECK: call void @llvm.memset.p0i8.i64(i8* %{{[0-9]+}}, i8 0, i64 24, i32 4, i1 false)
+call void @llvm.memset.p0i8.i64(i8* %p3, i8 0, i64 28, i32 4, i1 false)
+%neg2 = getelementptr inbounds i32* %p, i64 -2
+%arrayidx1 = bitcast i32* %neg2 to i64*
+store i64 1, i64* %arrayidx1, align 4
+ret void
+}
+
+declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1) nounwind
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