[llvm-commits] CVS: llvm/lib/Transforms/Scalar/ScalarReplAggregates.cpp
Chris Lattner
sabre at nondot.org
Tue May 29 23:11:45 PDT 2007
Changes in directory llvm/lib/Transforms/Scalar:
ScalarReplAggregates.cpp updated: 1.95 -> 1.96
---
Log message:
Fix Transforms/ScalarRepl/2007-05-29-MemcpyPreserve.ll and the second
half of PR1421: http://llvm.org/PR1421 , by not decimating structs with holes that are the source and
destination of a memcpy.
---
Diffs of the changes: (+148 -48)
ScalarReplAggregates.cpp | 196 +++++++++++++++++++++++++++++++++++------------
1 files changed, 148 insertions(+), 48 deletions(-)
Index: llvm/lib/Transforms/Scalar/ScalarReplAggregates.cpp
diff -u llvm/lib/Transforms/Scalar/ScalarReplAggregates.cpp:1.95 llvm/lib/Transforms/Scalar/ScalarReplAggregates.cpp:1.96
--- llvm/lib/Transforms/Scalar/ScalarReplAggregates.cpp:1.95 Thu May 24 13:43:04 2007
+++ llvm/lib/Transforms/Scalar/ScalarReplAggregates.cpp Wed May 30 01:11:23 2007
@@ -65,11 +65,41 @@
}
private:
- int isSafeElementUse(Value *Ptr, bool isFirstElt, AllocationInst *AI);
- int isSafeUseOfAllocation(Instruction *User, AllocationInst *AI);
- bool isSafeMemIntrinsicOnAllocation(MemIntrinsic *MI, AllocationInst *AI);
- bool isSafeUseOfBitCastedAllocation(BitCastInst *User, AllocationInst *AI);
+ /// AllocaInfo - When analyzing uses of an alloca instruction, this captures
+ /// information about the uses. All these fields are initialized to false
+ /// and set to true when something is learned.
+ struct AllocaInfo {
+ /// isUnsafe - This is set to true if the alloca cannot be SROA'd.
+ bool isUnsafe : 1;
+
+ /// needsCanon - This is set to true if there is some use of the alloca
+ /// that requires canonicalization.
+ bool needsCanon : 1;
+
+ /// isMemCpySrc - This is true if this aggregate is memcpy'd from.
+ bool isMemCpySrc : 1;
+
+ /// isMemCpyDst - This is true if this aggregate is memcpy'd info.
+ bool isMemCpyDst : 1;
+
+ AllocaInfo()
+ : isUnsafe(false), needsCanon(false),
+ isMemCpySrc(false), isMemCpyDst(false) {}
+ };
+
+ void MarkUnsafe(AllocaInfo &I) { I.isUnsafe = true; }
+
int isSafeAllocaToScalarRepl(AllocationInst *AI);
+
+ void isSafeUseOfAllocation(Instruction *User, AllocationInst *AI,
+ AllocaInfo &Info);
+ void isSafeElementUse(Value *Ptr, bool isFirstElt, AllocationInst *AI,
+ AllocaInfo &Info);
+ void isSafeMemIntrinsicOnAllocation(MemIntrinsic *MI, AllocationInst *AI,
+ unsigned OpNo, AllocaInfo &Info);
+ void isSafeUseOfBitCastedAllocation(BitCastInst *User, AllocationInst *AI,
+ AllocaInfo &Info);
+
void DoScalarReplacement(AllocationInst *AI,
std::vector<AllocationInst*> &WorkList);
void CanonicalizeAllocaUsers(AllocationInst *AI);
@@ -320,7 +350,8 @@
/// getelementptr instruction of an array aggregate allocation. isFirstElt
/// indicates whether Ptr is known to the start of the aggregate.
///
-int SROA::isSafeElementUse(Value *Ptr, bool isFirstElt, AllocationInst *AI) {
+void SROA::isSafeElementUse(Value *Ptr, bool isFirstElt, AllocationInst *AI,
+ AllocaInfo &Info) {
for (Value::use_iterator I = Ptr->use_begin(), E = Ptr->use_end();
I != E; ++I) {
Instruction *User = cast<Instruction>(*I);
@@ -328,7 +359,7 @@
case Instruction::Load: break;
case Instruction::Store:
// Store is ok if storing INTO the pointer, not storing the pointer
- if (User->getOperand(0) == Ptr) return 0;
+ if (User->getOperand(0) == Ptr) return MarkUnsafe(Info);
break;
case Instruction::GetElementPtr: {
GetElementPtrInst *GEP = cast<GetElementPtrInst>(User);
@@ -336,7 +367,8 @@
if (GEP->getNumOperands() > 1) {
if (!isa<ConstantInt>(GEP->getOperand(1)) ||
!cast<ConstantInt>(GEP->getOperand(1))->isZero())
- return 0; // Using pointer arithmetic to navigate the array.
+ // Using pointer arithmetic to navigate the array.
+ return MarkUnsafe(Info);
if (AreAllZeroIndices) {
for (unsigned i = 2, e = GEP->getNumOperands(); i != e; ++i) {
@@ -348,28 +380,34 @@
}
}
}
- if (!isSafeElementUse(GEP, AreAllZeroIndices, AI)) return 0;
+ isSafeElementUse(GEP, AreAllZeroIndices, AI, Info);
+ if (Info.isUnsafe) return;
break;
}
case Instruction::BitCast:
- if (isFirstElt &&
- isSafeUseOfBitCastedAllocation(cast<BitCastInst>(User), AI))
+ if (isFirstElt) {
+ isSafeUseOfBitCastedAllocation(cast<BitCastInst>(User), AI, Info);
+ if (Info.isUnsafe) return;
break;
+ }
DOUT << " Transformation preventing inst: " << *User;
- return 0;
+ return MarkUnsafe(Info);
case Instruction::Call:
if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) {
- if (isFirstElt && isSafeMemIntrinsicOnAllocation(MI, AI))
+ if (isFirstElt) {
+ isSafeMemIntrinsicOnAllocation(MI, AI, I.getOperandNo(), Info);
+ if (Info.isUnsafe) return;
break;
+ }
}
DOUT << " Transformation preventing inst: " << *User;
- return 0;
+ return MarkUnsafe(Info);
default:
DOUT << " Transformation preventing inst: " << *User;
- return 0;
+ return MarkUnsafe(Info);
}
}
- return 3; // All users look ok :)
+ return; // All users look ok :)
}
/// AllUsersAreLoads - Return true if all users of this value are loads.
@@ -384,21 +422,25 @@
/// isSafeUseOfAllocation - Check to see if this user is an allowed use for an
/// aggregate allocation.
///
-int SROA::isSafeUseOfAllocation(Instruction *User, AllocationInst *AI) {
+void SROA::isSafeUseOfAllocation(Instruction *User, AllocationInst *AI,
+ AllocaInfo &Info) {
if (BitCastInst *C = dyn_cast<BitCastInst>(User))
- return isSafeUseOfBitCastedAllocation(C, AI) ? 3 : 0;
- if (!isa<GetElementPtrInst>(User)) return 0;
+ return isSafeUseOfBitCastedAllocation(C, AI, Info);
+
+ GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User);
+ if (GEPI == 0)
+ return MarkUnsafe(Info);
- GetElementPtrInst *GEPI = cast<GetElementPtrInst>(User);
gep_type_iterator I = gep_type_begin(GEPI), E = gep_type_end(GEPI);
// The GEP is not safe to transform if not of the form "GEP <ptr>, 0, <cst>".
if (I == E ||
- I.getOperand() != Constant::getNullValue(I.getOperand()->getType()))
- return 0;
+ I.getOperand() != Constant::getNullValue(I.getOperand()->getType())) {
+ return MarkUnsafe(Info);
+ }
++I;
- if (I == E) return 0; // ran out of GEP indices??
+ if (I == E) return MarkUnsafe(Info); // ran out of GEP indices??
bool IsAllZeroIndices = true;
@@ -413,7 +455,7 @@
// something funny is going on, so we won't do the optimization.
//
if (Idx->getZExtValue() >= NumElements)
- return 0;
+ return MarkUnsafe(Info);
// We cannot scalar repl this level of the array unless any array
// sub-indices are in-range constants. In particular, consider:
@@ -430,9 +472,9 @@
NumElements = cast<VectorType>(*I)->getNumElements();
ConstantInt *IdxVal = dyn_cast<ConstantInt>(I.getOperand());
- if (!IdxVal) return 0;
+ if (!IdxVal) return MarkUnsafe(Info);
if (IdxVal->getZExtValue() >= NumElements)
- return 0;
+ return MarkUnsafe(Info);
IsAllZeroIndices &= IdxVal->isZero();
}
@@ -444,53 +486,62 @@
// it, in which case we CAN promote it, but we have to canonicalize this
// out if this is the only problem.
if ((NumElements == 1 || NumElements == 2) &&
- AllUsersAreLoads(GEPI))
- return 1; // Canonicalization required!
- return 0;
+ AllUsersAreLoads(GEPI)) {
+ Info.needsCanon = true;
+ return; // Canonicalization required!
+ }
+ return MarkUnsafe(Info);
}
}
// If there are any non-simple uses of this getelementptr, make sure to reject
// them.
- return isSafeElementUse(GEPI, IsAllZeroIndices, AI);
+ return isSafeElementUse(GEPI, IsAllZeroIndices, AI, Info);
}
/// isSafeMemIntrinsicOnAllocation - Return true if the specified memory
/// intrinsic can be promoted by SROA. At this point, we know that the operand
/// of the memintrinsic is a pointer to the beginning of the allocation.
-bool SROA::isSafeMemIntrinsicOnAllocation(MemIntrinsic *MI, AllocationInst *AI){
+void SROA::isSafeMemIntrinsicOnAllocation(MemIntrinsic *MI, AllocationInst *AI,
+ unsigned OpNo, AllocaInfo &Info) {
// If not constant length, give up.
ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength());
- if (!Length) return false;
+ if (!Length) return MarkUnsafe(Info);
// If not the whole aggregate, give up.
const TargetData &TD = getAnalysis<TargetData>();
if (Length->getZExtValue() != TD.getTypeSize(AI->getType()->getElementType()))
- return false;
+ return MarkUnsafe(Info);
// We only know about memcpy/memset/memmove.
if (!isa<MemCpyInst>(MI) && !isa<MemSetInst>(MI) && !isa<MemMoveInst>(MI))
- return false;
- // Otherwise, we can transform it.
- return true;
+ return MarkUnsafe(Info);
+
+ // Otherwise, we can transform it. Determine whether this is a memcpy/set
+ // into or out of the aggregate.
+ if (OpNo == 1)
+ Info.isMemCpyDst = true;
+ else {
+ assert(OpNo == 2);
+ Info.isMemCpySrc = true;
+ }
}
/// isSafeUseOfBitCastedAllocation - Return true if all users of this bitcast
/// are
-bool SROA::isSafeUseOfBitCastedAllocation(BitCastInst *BC, AllocationInst *AI) {
+void SROA::isSafeUseOfBitCastedAllocation(BitCastInst *BC, AllocationInst *AI,
+ AllocaInfo &Info) {
for (Value::use_iterator UI = BC->use_begin(), E = BC->use_end();
UI != E; ++UI) {
if (BitCastInst *BCU = dyn_cast<BitCastInst>(UI)) {
- if (!isSafeUseOfBitCastedAllocation(BCU, AI))
- return false;
+ isSafeUseOfBitCastedAllocation(BCU, AI, Info);
} else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(UI)) {
- if (!isSafeMemIntrinsicOnAllocation(MI, AI))
- return false;
+ isSafeMemIntrinsicOnAllocation(MI, AI, UI.getOperandNo(), Info);
} else {
- return false;
+ return MarkUnsafe(Info);
}
+ if (Info.isUnsafe) return;
}
- return true;
}
/// RewriteBitCastUserOfAlloca - BCInst (transitively) bitcasts AI, or indexes
@@ -668,6 +719,44 @@
}
}
+/// HasStructPadding - Return true if the specified type has any structure
+/// padding, false otherwise.
+static bool HasStructPadding(const Type *Ty, const TargetData &TD) {
+ if (const StructType *STy = dyn_cast<StructType>(Ty)) {
+ const StructLayout *SL = TD.getStructLayout(STy);
+ unsigned PrevFieldBitOffset = 0;
+ for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
+ unsigned FieldBitOffset = SL->getElementOffset(i)*8;
+
+ // Padding in sub-elements?
+ if (HasStructPadding(STy->getElementType(i), TD))
+ return true;
+
+ // Check to see if there is any padding between this element and the
+ // previous one.
+ if (i) {
+ unsigned PrevFieldEnd =
+ PrevFieldBitOffset+TD.getTypeSizeInBits(STy->getElementType(i-1));
+ if (PrevFieldEnd < FieldBitOffset)
+ return true;
+ }
+
+ PrevFieldBitOffset = FieldBitOffset;
+ }
+
+ // Check for tail padding.
+ if (unsigned EltCount = STy->getNumElements()) {
+ unsigned PrevFieldEnd = PrevFieldBitOffset +
+ TD.getTypeSizeInBits(STy->getElementType(EltCount-1));
+ if (PrevFieldEnd < SL->getSizeInBytes()*8)
+ return true;
+ }
+
+ } else if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
+ return HasStructPadding(ATy->getElementType(), TD);
+ }
+ return false;
+}
/// isSafeStructAllocaToScalarRepl - Check to see if the specified allocation of
/// an aggregate can be broken down into elements. Return 0 if not, 3 if safe,
@@ -676,18 +765,29 @@
int SROA::isSafeAllocaToScalarRepl(AllocationInst *AI) {
// Loop over the use list of the alloca. We can only transform it if all of
// the users are safe to transform.
- //
- int isSafe = 3;
+ AllocaInfo Info;
+
for (Value::use_iterator I = AI->use_begin(), E = AI->use_end();
I != E; ++I) {
- isSafe &= isSafeUseOfAllocation(cast<Instruction>(*I), AI);
- if (isSafe == 0) {
+ isSafeUseOfAllocation(cast<Instruction>(*I), AI, Info);
+ if (Info.isUnsafe) {
DOUT << "Cannot transform: " << *AI << " due to user: " << **I;
return 0;
}
}
- // If we require cleanup, isSafe is now 1, otherwise it is 3.
- return isSafe;
+
+ // Okay, we know all the users are promotable. If the aggregate is a memcpy
+ // source and destination, we have to be careful. In particular, the memcpy
+ // could be moving around elements that live in structure padding of the LLVM
+ // types, but may actually be used. In these cases, we refuse to promote the
+ // struct.
+ if (Info.isMemCpySrc && Info.isMemCpyDst &&
+ HasStructPadding(AI->getType()->getElementType(),
+ getAnalysis<TargetData>()))
+ return 0;
+
+ // If we require cleanup, return 1, otherwise return 3.
+ return Info.needsCanon ? 1 : 3;
}
/// CanonicalizeAllocaUsers - If SROA reported that it can promote the specified
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