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-rw-r--r--lib/VMCore/ConstantFold.cpp193
1 files changed, 169 insertions, 24 deletions
diff --git a/lib/VMCore/ConstantFold.cpp b/lib/VMCore/ConstantFold.cpp
index 40061ee..c22c3e9 100644
--- a/lib/VMCore/ConstantFold.cpp
+++ b/lib/VMCore/ConstantFold.cpp
@@ -323,6 +323,116 @@ static Constant *ExtractConstantBytes(Constant *C, unsigned ByteStart,
}
}
+/// getFoldedSizeOf - Return a ConstantExpr with type DestTy for sizeof
+/// on Ty, with any known factors factored out. If Folded is false,
+/// return null if no factoring was possible, to avoid endlessly
+/// bouncing an unfoldable expression back into the top-level folder.
+///
+static Constant *getFoldedSizeOf(const Type *Ty, const Type *DestTy,
+ bool Folded) {
+ if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
+ Constant *N = ConstantInt::get(DestTy, ATy->getNumElements());
+ Constant *E = getFoldedSizeOf(ATy->getElementType(), DestTy, true);
+ return ConstantExpr::getNUWMul(E, N);
+ }
+ if (const VectorType *VTy = dyn_cast<VectorType>(Ty)) {
+ Constant *N = ConstantInt::get(DestTy, VTy->getNumElements());
+ Constant *E = getFoldedSizeOf(VTy->getElementType(), DestTy, true);
+ return ConstantExpr::getNUWMul(E, N);
+ }
+ if (const StructType *STy = dyn_cast<StructType>(Ty))
+ if (!STy->isPacked()) {
+ unsigned NumElems = STy->getNumElements();
+ // An empty struct has size zero.
+ if (NumElems == 0)
+ return ConstantExpr::getNullValue(DestTy);
+ // Check for a struct with all members having the same type.
+ const Type *MemberTy = STy->getElementType(0);
+ bool AllSame = true;
+ for (unsigned i = 1; i != NumElems; ++i)
+ if (MemberTy != STy->getElementType(i)) {
+ AllSame = false;
+ break;
+ }
+ if (AllSame) {
+ Constant *N = ConstantInt::get(DestTy, NumElems);
+ Constant *E = getFoldedSizeOf(MemberTy, DestTy, true);
+ return ConstantExpr::getNUWMul(E, N);
+ }
+ }
+
+ // If there's no interesting folding happening, bail so that we don't create
+ // a constant that looks like it needs folding but really doesn't.
+ if (!Folded)
+ return 0;
+
+ // Base case: Get a regular sizeof expression.
+ Constant *C = ConstantExpr::getSizeOf(Ty);
+ C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false,
+ DestTy, false),
+ C, DestTy);
+ return C;
+}
+
+/// getFoldedOffsetOf - Return a ConstantExpr with type DestTy for offsetof
+/// on Ty and FieldNo, with any known factors factored out. If Folded is false,
+/// return null if no factoring was possible, to avoid endlessly
+/// bouncing an unfoldable expression back into the top-level folder.
+///
+static Constant *getFoldedOffsetOf(const Type *Ty, Constant *FieldNo,
+ const Type *DestTy,
+ bool Folded) {
+ if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
+ Constant *N = ConstantExpr::getCast(CastInst::getCastOpcode(FieldNo, false,
+ DestTy, false),
+ FieldNo, DestTy);
+ Constant *E = getFoldedSizeOf(ATy->getElementType(), DestTy, true);
+ return ConstantExpr::getNUWMul(E, N);
+ }
+ if (const VectorType *VTy = dyn_cast<VectorType>(Ty)) {
+ Constant *N = ConstantExpr::getCast(CastInst::getCastOpcode(FieldNo, false,
+ DestTy, false),
+ FieldNo, DestTy);
+ Constant *E = getFoldedSizeOf(VTy->getElementType(), DestTy, true);
+ return ConstantExpr::getNUWMul(E, N);
+ }
+ if (const StructType *STy = dyn_cast<StructType>(Ty))
+ if (!STy->isPacked()) {
+ unsigned NumElems = STy->getNumElements();
+ // An empty struct has no members.
+ if (NumElems == 0)
+ return 0;
+ // Check for a struct with all members having the same type.
+ const Type *MemberTy = STy->getElementType(0);
+ bool AllSame = true;
+ for (unsigned i = 1; i != NumElems; ++i)
+ if (MemberTy != STy->getElementType(i)) {
+ AllSame = false;
+ break;
+ }
+ if (AllSame) {
+ Constant *N = ConstantExpr::getCast(CastInst::getCastOpcode(FieldNo,
+ false,
+ DestTy,
+ false),
+ FieldNo, DestTy);
+ Constant *E = getFoldedSizeOf(MemberTy, DestTy, true);
+ return ConstantExpr::getNUWMul(E, N);
+ }
+ }
+
+ // If there's no interesting folding happening, bail so that we don't create
+ // a constant that looks like it needs folding but really doesn't.
+ if (!Folded)
+ return 0;
+
+ // Base case: Get a regular offsetof expression.
+ Constant *C = ConstantExpr::getOffsetOf(Ty, FieldNo);
+ C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false,
+ DestTy, false),
+ C, DestTy);
+ return C;
+}
Constant *llvm::ConstantFoldCastInstruction(LLVMContext &Context,
unsigned opc, Constant *V,
@@ -418,33 +528,59 @@ Constant *llvm::ConstantFoldCastInstruction(LLVMContext &Context,
// Is it a null pointer value?
if (V->isNullValue())
return ConstantInt::get(DestTy, 0);
- // If this is a sizeof of an array or vector, pull out a multiplication
- // by the element size to expose it to subsequent folding.
+ // If this is a sizeof-like expression, pull out multiplications by
+ // known factors to expose them to subsequent folding. If it's an
+ // alignof-like expression, factor out known factors.
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
if (CE->getOpcode() == Instruction::GetElementPtr &&
- CE->getNumOperands() == 2 &&
- CE->getOperand(0)->isNullValue())
- if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(1)))
- if (CI->isOne()) {
- const Type *Ty =
- cast<PointerType>(CE->getOperand(0)->getType())->getElementType();
- if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
- Constant *N = ConstantInt::get(DestTy, ATy->getNumElements());
- Constant *E = ConstantExpr::getSizeOf(ATy->getElementType());
- E = ConstantExpr::getCast(CastInst::getCastOpcode(E, false,
+ CE->getOperand(0)->isNullValue()) {
+ const Type *Ty =
+ cast<PointerType>(CE->getOperand(0)->getType())->getElementType();
+ if (CE->getNumOperands() == 2) {
+ // Handle a sizeof-like expression.
+ Constant *Idx = CE->getOperand(1);
+ bool isOne = isa<ConstantInt>(Idx) && cast<ConstantInt>(Idx)->isOne();
+ if (Constant *C = getFoldedSizeOf(Ty, DestTy, !isOne)) {
+ Idx = ConstantExpr::getCast(CastInst::getCastOpcode(Idx, true,
DestTy, false),
- E, DestTy);
- return ConstantExpr::getMul(N, E);
- }
- if (const VectorType *VTy = dyn_cast<VectorType>(Ty)) {
- Constant *N = ConstantInt::get(DestTy, VTy->getNumElements());
- Constant *E = ConstantExpr::getSizeOf(VTy->getElementType());
- E = ConstantExpr::getCast(CastInst::getCastOpcode(E, false,
- DestTy, false),
- E, DestTy);
- return ConstantExpr::getMul(N, E);
+ Idx, DestTy);
+ return ConstantExpr::getMul(C, Idx);
+ }
+ } else if (CE->getNumOperands() == 3 &&
+ CE->getOperand(1)->isNullValue()) {
+ // Handle an alignof-like expression.
+ if (const StructType *STy = dyn_cast<StructType>(Ty))
+ if (!STy->isPacked()) {
+ ConstantInt *CI = cast<ConstantInt>(CE->getOperand(2));
+ if (CI->isOne() &&
+ STy->getNumElements() == 2 &&
+ STy->getElementType(0)->isInteger(1)) {
+ // The alignment of an array is equal to the alignment of the
+ // array element. Note that this is not always true for vectors.
+ if (const ArrayType *ATy =
+ dyn_cast<ArrayType>(STy->getElementType(1))) {
+ Constant *C = ConstantExpr::getAlignOf(ATy->getElementType());
+ C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false,
+ DestTy,
+ false),
+ C, DestTy);
+ return C;
+ }
+ // Packed structs always have an alignment of 1.
+ if (const StructType *InnerSTy =
+ dyn_cast<StructType>(STy->getElementType(1)))
+ if (InnerSTy->isPacked())
+ return ConstantInt::get(DestTy, 1);
+ }
}
+ // Handle an offsetof-like expression.
+ if (isa<StructType>(Ty) || isa<ArrayType>(Ty) || isa<VectorType>(Ty)){
+ if (Constant *C = getFoldedOffsetOf(Ty, CE->getOperand(2),
+ DestTy, false))
+ return C;
}
+ }
+ }
// Other pointer types cannot be casted
return 0;
case Instruction::UIToFP:
@@ -1156,10 +1292,19 @@ Constant *llvm::ConstantFoldBinaryInstruction(LLVMContext &Context,
}
}
- if (isa<ConstantExpr>(C1)) {
+ if (ConstantExpr *CE1 = dyn_cast<ConstantExpr>(C1)) {
// There are many possible foldings we could do here. We should probably
// at least fold add of a pointer with an integer into the appropriate
// getelementptr. This will improve alias analysis a bit.
+
+ // Given ((a + b) + c), if (b + c) folds to something interesting, return
+ // (a + (b + c)).
+ if (Instruction::isAssociative(Opcode, C1->getType()) &&
+ CE1->getOpcode() == Opcode) {
+ Constant *T = ConstantExpr::get(Opcode, CE1->getOperand(1), C2);
+ if (!isa<ConstantExpr>(T) || cast<ConstantExpr>(T)->getOpcode() != Opcode)
+ return ConstantExpr::get(Opcode, CE1->getOperand(0), T);
+ }
} else if (isa<ConstantExpr>(C2)) {
// If C2 is a constant expr and C1 isn't, flop them around and fold the
// other way if possible.
@@ -2004,7 +2149,7 @@ Constant *llvm::ConstantFoldGetElementPtr(LLVMContext &Context,
}
// Implement folding of:
- // int* getelementptr ([2 x int]* cast ([3 x int]* %X to [2 x int]*),
+ // int* getelementptr ([2 x int]* bitcast ([3 x int]* %X to [2 x int]*),
// long 0, long 0)
// To: int* getelementptr ([3 x int]* %X, long 0, long 0)
//
generated by cgit v1.1 at 2025-06-13 03:00:33 +0000