[llvm-commits] [llvm] r143630 - in /llvm/trunk: lib/Transforms/Scalar/DeadStoreElimination.cpp test/Transforms/DeadStoreElimination/OverwriteStoreEnd.ll
Pete Cooper
peter_cooper at apple.com
Thu Nov 3 11:01:56 PDT 2011
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>
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
More information about the llvm-commits
mailing list