[llvm-commits] [llvm] r86359 - in /llvm/trunk: lib/Transforms/Scalar/DeadStoreElimination.cpp test/Transforms/DeadStoreElimination/lifetime.ll test/Transforms/DeadStoreElimination/memintrinsics.ll
Nick Lewycky
nicholas at mxc.ca
Sat Nov 7 00:34:41 PST 2009
Author: nicholas
Date: Sat Nov 7 02:34:40 2009
New Revision: 86359
URL: http://llvm.org/viewvc/llvm-project?rev=86359&view=rev
Log:
Teach dead store elimination that certain intrinsics write to memory just like
a store.
Added:
llvm/trunk/test/Transforms/DeadStoreElimination/lifetime.ll
llvm/trunk/test/Transforms/DeadStoreElimination/memintrinsics.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=86359&r1=86358&r2=86359&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp Sat Nov 7 02:34:40 2009
@@ -78,19 +78,84 @@
FunctionPass *llvm::createDeadStoreEliminationPass() { return new DSE(); }
-/// isValueAtLeastAsBigAs - Return true if V1 is greater than or equal to the
-/// stored size of V2. This returns false if we don't know.
+/// doesClobberMemory - Does this instruction clobber (write without reading)
+/// some memory?
+static bool doesClobberMemory(Instruction *I) {
+ if (isa<StoreInst>(I))
+ return true;
+ if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
+ switch (II->getIntrinsicID()) {
+ default: return false;
+ case Intrinsic::memset: case Intrinsic::memmove: case Intrinsic::memcpy:
+ case Intrinsic::lifetime_end: return true;
+ }
+ }
+ return false;
+}
+
+/// isElidable - If the memory this instruction and the memory it writes to is
+/// unused, may we delete this instrtction?
+static bool isElidable(Instruction *I) {
+ assert(doesClobberMemory(I));
+ if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
+ return II->getIntrinsicID() != Intrinsic::lifetime_end;
+ if (StoreInst *SI = dyn_cast<StoreInst>(I))
+ return !SI->isVolatile();
+ return true;
+}
+
+/// getPointerOperand - Return the pointer that is being clobbered.
+static Value *getPointerOperand(Instruction *I) {
+ assert(doesClobberMemory(I));
+ if (StoreInst *SI = dyn_cast<StoreInst>(I))
+ return SI->getPointerOperand();
+ if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I))
+ return MI->getOperand(1);
+ assert(cast<IntrinsicInst>(I)->getIntrinsicID() == Intrinsic::lifetime_end);
+ return cast<IntrinsicInst>(I)->getOperand(2);
+}
+
+/// getStoreSize - Return the length in bytes of the write by the clobbering
+/// instruction. If variable or unknown, returns -1.
+static unsigned getStoreSize(Instruction *I, const TargetData *TD = 0) {
+ assert(doesClobberMemory(I));
+ if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
+ if (!TD) return -1u;
+ const PointerType *PTy =
+ cast<PointerType>(SI->getPointerOperand()->getType());
+ return TD->getTypeStoreSize(PTy);
+ }
+
+ Value *Len;
+ if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
+ Len = MI->getLength();
+ } else {
+ assert(cast<IntrinsicInst>(I)->getIntrinsicID() ==
+ Intrinsic::lifetime_end);
+ Len = cast<IntrinsicInst>(I)->getOperand(0);
+ }
+ if (ConstantInt *LenCI = dyn_cast<ConstantInt>(Len))
+ if (!LenCI->isAllOnesValue())
+ return LenCI->getZExtValue();
+ return -1u;
+}
+
+/// isStoreAtLeastAsWideAs - Return true if the size of the store in I1 is
+/// greater than or equal to the store in I2. This returns false if we don't
+/// know.
///
-static bool isValueAtLeastAsBigAs(Value *V1, Value *V2, const TargetData *TD) {
- const Type *V1Ty = V1->getType(), *V2Ty = V2->getType();
+static bool isStoreAtLeastAsWideAs(Instruction *I1, Instruction *I2,
+ const TargetData *TD) {
+ const Type *I1Ty = getPointerOperand(I1)->getType();
+ const Type *I2Ty = getPointerOperand(I2)->getType();
// Exactly the same type, must have exactly the same size.
- if (V1Ty == V2Ty) return true;
+ if (I1Ty == I2Ty) return true;
- // If we don't have target data, we don't know.
- if (TD == 0) return false;
+ int I1Size = getStoreSize(I1, TD);
+ int I2Size = getStoreSize(I2, TD);
- return TD->getTypeStoreSize(V1Ty) >= TD->getTypeStoreSize(V2Ty);
+ return I1Size != -1 && I2Size != -1 && I1Size >= I2Size;
}
bool DSE::runOnBasicBlock(BasicBlock &BB) {
@@ -104,14 +169,9 @@
Instruction *Inst = BBI++;
// If we find a store or a free, get its memory dependence.
- if (!isa<StoreInst>(Inst) && !isFreeCall(Inst))
+ if (!doesClobberMemory(Inst) && !isFreeCall(Inst))
continue;
- // Don't molest volatile stores or do queries that will return "clobber".
- if (StoreInst *SI = dyn_cast<StoreInst>(Inst))
- if (SI->isVolatile())
- continue;
-
MemDepResult InstDep = MD.getDependency(Inst);
// Ignore non-local stores.
@@ -124,16 +184,16 @@
continue;
}
- StoreInst *SI = cast<StoreInst>(Inst);
-
// If not a definite must-alias dependency, ignore it.
if (!InstDep.isDef())
continue;
// If this is a store-store dependence, then the previous store is dead so
// long as this store is at least as big as it.
- if (StoreInst *DepStore = dyn_cast<StoreInst>(InstDep.getInst()))
- if (isValueAtLeastAsBigAs(SI->getOperand(0), DepStore->getOperand(0),TD)){
+ if (doesClobberMemory(InstDep.getInst())) {
+ Instruction *DepStore = InstDep.getInst();
+ if (isStoreAtLeastAsWideAs(Inst, DepStore, TD) &&
+ isElidable(DepStore)){
// Delete the store and now-dead instructions that feed it.
DeleteDeadInstruction(DepStore);
NumFastStores++;
@@ -146,25 +206,31 @@
--BBI;
continue;
}
+ }
+
+ if (!isElidable(Inst))
+ continue;
// If we're storing the same value back to a pointer that we just
// loaded from, then the store can be removed.
- if (LoadInst *DepLoad = dyn_cast<LoadInst>(InstDep.getInst())) {
- if (SI->getPointerOperand() == DepLoad->getPointerOperand() &&
- SI->getOperand(0) == DepLoad) {
- // DeleteDeadInstruction can delete the current instruction. Save BBI
- // in case we need it.
- WeakVH NextInst(BBI);
-
- DeleteDeadInstruction(SI);
-
- if (NextInst == 0) // Next instruction deleted.
- BBI = BB.begin();
- else if (BBI != BB.begin()) // Revisit this instruction if possible.
- --BBI;
- NumFastStores++;
- MadeChange = true;
- continue;
+ if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
+ if (LoadInst *DepLoad = dyn_cast<LoadInst>(InstDep.getInst())) {
+ if (SI->getPointerOperand() == DepLoad->getPointerOperand() &&
+ SI->getOperand(0) == DepLoad) {
+ // DeleteDeadInstruction can delete the current instruction. Save BBI
+ // in case we need it.
+ WeakVH NextInst(BBI);
+
+ DeleteDeadInstruction(SI);
+
+ if (NextInst == 0) // Next instruction deleted.
+ BBI = BB.begin();
+ else if (BBI != BB.begin()) // Revisit this instruction if possible.
+ --BBI;
+ NumFastStores++;
+ MadeChange = true;
+ continue;
+ }
}
}
@@ -176,7 +242,7 @@
// in case we need it.
WeakVH NextInst(BBI);
- DeleteDeadInstruction(SI);
+ DeleteDeadInstruction(Inst);
if (NextInst == 0) // Next instruction deleted.
BBI = BB.begin();
@@ -202,11 +268,11 @@
bool DSE::handleFreeWithNonTrivialDependency(Instruction *F, MemDepResult Dep) {
AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
- StoreInst *Dependency = dyn_cast_or_null<StoreInst>(Dep.getInst());
- if (!Dependency || Dependency->isVolatile())
+ Instruction *Dependency = Dep.getInst();
+ if (!Dependency || !doesClobberMemory(Dependency) || !isElidable(Dependency))
return false;
- Value *DepPointer = Dependency->getPointerOperand()->getUnderlyingObject();
+ Value *DepPointer = getPointerOperand(Dependency)->getUnderlyingObject();
// Check for aliasing.
if (AA.alias(F->getOperand(1), 1, DepPointer, 1) !=
@@ -251,39 +317,28 @@
--BBI;
// If we find a store whose pointer is dead.
- if (StoreInst* S = dyn_cast<StoreInst>(BBI)) {
- if (!S->isVolatile()) {
+ if (doesClobberMemory(BBI)) {
+ if (isElidable(BBI)) {
// See through pointer-to-pointer bitcasts
- Value* pointerOperand = S->getPointerOperand()->getUnderlyingObject();
+ Value *pointerOperand = getPointerOperand(BBI)->getUnderlyingObject();
// Alloca'd pointers or byval arguments (which are functionally like
// alloca's) are valid candidates for removal.
if (deadPointers.count(pointerOperand)) {
// DCE instructions only used to calculate that store.
+ Instruction *Dead = BBI;
BBI++;
- DeleteDeadInstruction(S, &deadPointers);
+ DeleteDeadInstruction(Dead, &deadPointers);
NumFastStores++;
MadeChange = true;
+ continue;
}
}
- continue;
- }
-
- // We can also remove memcpy's to local variables at the end of a function.
- if (MemCpyInst *M = dyn_cast<MemCpyInst>(BBI)) {
- Value *dest = M->getDest()->getUnderlyingObject();
-
- if (deadPointers.count(dest)) {
- BBI++;
- DeleteDeadInstruction(M, &deadPointers);
- NumFastOther++;
- MadeChange = true;
+ // Because a memcpy or memmove is also a load, we can't skip it if we
+ // didn't remove it.
+ if (!isa<MemTransferInst>(BBI))
continue;
- }
-
- // Because a memcpy is also a load, we can't skip it if we didn't remove
- // it.
}
Value* killPointer = 0;
@@ -304,11 +359,11 @@
killPointer = L->getPointerOperand();
} else if (VAArgInst* V = dyn_cast<VAArgInst>(BBI)) {
killPointer = V->getOperand(0);
- } else if (isa<MemCpyInst>(BBI) &&
- isa<ConstantInt>(cast<MemCpyInst>(BBI)->getLength())) {
- killPointer = cast<MemCpyInst>(BBI)->getSource();
+ } else if (isa<MemTransferInst>(BBI) &&
+ isa<ConstantInt>(cast<MemTransferInst>(BBI)->getLength())) {
+ killPointer = cast<MemTransferInst>(BBI)->getSource();
killPointerSize = cast<ConstantInt>(
- cast<MemCpyInst>(BBI)->getLength())->getZExtValue();
+ cast<MemTransferInst>(BBI)->getLength())->getZExtValue();
} else if (AllocaInst* A = dyn_cast<AllocaInst>(BBI)) {
deadPointers.erase(A);
Added: llvm/trunk/test/Transforms/DeadStoreElimination/lifetime.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/DeadStoreElimination/lifetime.ll?rev=86359&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/DeadStoreElimination/lifetime.ll (added)
+++ llvm/trunk/test/Transforms/DeadStoreElimination/lifetime.ll Sat Nov 7 02:34:40 2009
@@ -0,0 +1,19 @@
+; RUN: opt -S -dse < %s | FileCheck %s
+
+declare void @llvm.lifetime.end(i64, i8*)
+declare void @llvm.memset.i8(i8*, i8, i8, i32)
+
+define void @test1() {
+; CHECK: @test1
+ %A = alloca i8
+
+ store i8 0, i8* %A ;; Written to by memset
+ call void @llvm.lifetime.end(i64 1, i8* %A)
+; CHECK: lifetime.end
+
+ call void @llvm.memset.i8(i8* %A, i8 0, i8 -1, i32 0)
+; CHECK-NOT: memset
+
+ ret void
+; CHECK: ret void
+}
Added: llvm/trunk/test/Transforms/DeadStoreElimination/memintrinsics.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/DeadStoreElimination/memintrinsics.ll?rev=86359&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/DeadStoreElimination/memintrinsics.ll (added)
+++ llvm/trunk/test/Transforms/DeadStoreElimination/memintrinsics.ll Sat Nov 7 02:34:40 2009
@@ -0,0 +1,47 @@
+; RUN: opt -S -dse < %s | FileCheck %s
+
+declare void @llvm.memcpy.i8(i8*, i8*, i8, i32)
+declare void @llvm.memmove.i8(i8*, i8*, i8, i32)
+declare void @llvm.memset.i8(i8*, i8, i8, i32)
+
+define void @test1() {
+; CHECK: @test1
+ %A = alloca i8
+ %B = alloca i8
+
+ store i8 0, i8* %A ;; Written to by memcpy
+; CHECK-NOT: store
+
+ call void @llvm.memcpy.i8(i8* %A, i8* %B, i8 -1, i32 0)
+
+ ret void
+; CHECK: ret void
+}
+
+define void @test2() {
+; CHECK: @test2
+ %A = alloca i8
+ %B = alloca i8
+
+ store i8 0, i8* %A ;; Written to by memmove
+; CHECK-NOT: store
+
+ call void @llvm.memmove.i8(i8* %A, i8* %B, i8 -1, i32 0)
+
+ ret void
+; CHECK: ret void
+}
+
+define void @test3() {
+; CHECK: @test3
+ %A = alloca i8
+ %B = alloca i8
+
+ store i8 0, i8* %A ;; Written to by memset
+; CHECK-NOT: store
+
+ call void @llvm.memset.i8(i8* %A, i8 0, i8 -1, i32 0)
+
+ ret void
+; CHECK: ret void
+}
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