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Take alignment into account in isSafeToSpeculativelyExecute and isSafeToLoadUnconditionally. 

Reviewed By: hfinkel, sanjoy, MatzeB

Differential Revision: http://reviews.llvm.org/D9791

llvm-svn: 245223
This commit is contained in:
Artur Pilipenko 2015-08-17 15:54:26 +00:00
parent bb467f6f04
commit 34d8ba84c8
4 changed files with 158 additions and 52 deletions
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10
llvm/include/llvm/Analysis/ValueTracking.h
View File

@ -228,6 +228,16 @@ namespace llvm {
const Instruction *CtxI = nullptr,
const DominatorTree *DT = nullptr,
const TargetLibraryInfo *TLI = nullptr);
/// Returns true if V is always a dereferenceable pointer with alignment
/// greater or equal than requested. If the context instruction is specified
/// performs context-sensitive analysis and returns true if the pointer is
/// dereferenceable at the specified instruction.
bool isDereferenceableAndAlignedPointer(const Value *V, unsigned Align,
const DataLayout &DL,
const Instruction *CtxI = nullptr,
const DominatorTree *DT = nullptr,
const TargetLibraryInfo *TLI = nullptr);
/// isSafeToSpeculativelyExecute - Return true if the instruction does not
/// have any effects besides calculating the result and does not have

16
llvm/lib/Analysis/MemDerefPrinter.cpp
View File

@ -22,7 +22,8 @@ using namespace llvm;
namespace {
struct MemDerefPrinter : public FunctionPass {
SmallVector<Value *, 4> Vec;
SmallVector<Value *, 4> Deref;
SmallPtrSet<Value *, 4> DerefAndAligned;
static char ID; // Pass identification, replacement for typeid
MemDerefPrinter() : FunctionPass(ID) {
@ -34,7 +35,8 @@ namespace {
bool runOnFunction(Function &F) override;
void print(raw_ostream &OS, const Module * = nullptr) const override;
void releaseMemory() override {
Vec.clear();
Deref.clear();
DerefAndAligned.clear();
}
};
}
@ -55,7 +57,9 @@ bool MemDerefPrinter::runOnFunction(Function &F) {
if (LoadInst *LI = dyn_cast<LoadInst>(&I)) {
Value *PO = LI->getPointerOperand();
if (isDereferenceablePointer(PO, DL))
Vec.push_back(PO);
Deref.push_back(PO);
if (isDereferenceableAndAlignedPointer(PO, LI->getAlignment(), DL))
DerefAndAligned.insert(PO);
}
}
return false;
@ -63,8 +67,12 @@ bool MemDerefPrinter::runOnFunction(Function &F) {
void MemDerefPrinter::print(raw_ostream &OS, const Module *M) const {
OS << "The following are dereferenceable:\n";
for (auto &V: Vec) {
for (Value *V: Deref) {
V->print(OS);
if (DerefAndAligned.count(V))
OS << "\t(aligned)";
else
OS << "\t(unaligned)";
OS << "\n\n";
}
}

114
llvm/lib/Analysis/ValueTracking.cpp
View File

@ -2935,20 +2935,44 @@ static bool isDereferenceableFromAttribute(const Value *V, const DataLayout &DL,
return isDereferenceableFromAttribute(V, Offset, Ty, DL, CtxI, DT, TLI);
}
/// Return true if Value is always a dereferenceable pointer.
///
static bool isAligned(const Value *Base, APInt Offset, unsigned Align,
const DataLayout &DL) {
APInt BaseAlign(Offset.getBitWidth(), 0);
if (const AllocaInst *AI = dyn_cast<AllocaInst>(Base))
BaseAlign = AI->getAlignment();
else if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Base))
BaseAlign = GV->getAlignment();
else if (const Argument *A = dyn_cast<Argument>(Base))
BaseAlign = A->getParamAlignment();
if (!BaseAlign) {
Type *Ty = Base->getType()->getPointerElementType();
BaseAlign = DL.getABITypeAlignment(Ty);
}
APInt Alignment(Offset.getBitWidth(), Align);
assert(Alignment.isPowerOf2() && "must be a power of 2!");
return BaseAlign.uge(Alignment) && !(Offset & (Alignment-1));
}
static bool isAligned(const Value *Base, unsigned Align, const DataLayout &DL) {
APInt Offset(DL.getTypeStoreSizeInBits(Base->getType()), 0);
return isAligned(Base, Offset, Align, DL);
}
/// Test if V is always a pointer to allocated and suitably aligned memory for
/// a simple load or store.
static bool isDereferenceablePointer(const Value *V, const DataLayout &DL,
const Instruction *CtxI,
const DominatorTree *DT,
const TargetLibraryInfo *TLI,
SmallPtrSetImpl<const Value *> &Visited) {
static bool isDereferenceableAndAlignedPointer(
const Value *V, unsigned Align, const DataLayout &DL,
const Instruction *CtxI, const DominatorTree *DT,
const TargetLibraryInfo *TLI, SmallPtrSetImpl<const Value *> &Visited) {
// Note that it is not safe to speculate into a malloc'd region because
// malloc may return null.
// These are obviously ok.
if (isa<AllocaInst>(V)) return true;
// These are obviously ok if aligned.
if (isa<AllocaInst>(V))
return isAligned(V, Align, DL);
// It's not always safe to follow a bitcast, for example:
// bitcast i8* (alloca i8) to i32*
@ -2963,21 +2987,22 @@ static bool isDereferenceablePointer(const Value *V, const DataLayout &DL,
if (STy->isSized() && DTy->isSized() &&
(DL.getTypeStoreSize(STy) >= DL.getTypeStoreSize(DTy)) &&
(DL.getABITypeAlignment(STy) >= DL.getABITypeAlignment(DTy)))
return isDereferenceablePointer(BC->getOperand(0), DL, CtxI,
DT, TLI, Visited);
return isDereferenceableAndAlignedPointer(BC->getOperand(0), Align, DL,
CtxI, DT, TLI, Visited);
}
// Global variables which can't collapse to null are ok.
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
return !GV->hasExternalWeakLinkage();
if (!GV->hasExternalWeakLinkage())
return isAligned(V, Align, DL);
// byval arguments are okay.
if (const Argument *A = dyn_cast<Argument>(V))
if (A->hasByValAttr())
return true;
return isAligned(V, Align, DL);
if (isDereferenceableFromAttribute(V, DL, CtxI, DT, TLI))
return true;
return isAligned(V, Align, DL);
// For GEPs, determine if the indexing lands within the allocated object.
if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
@ -2985,61 +3010,79 @@ static bool isDereferenceablePointer(const Value *V, const DataLayout &DL,
Type *Ty = VTy->getPointerElementType();
const Value *Base = GEP->getPointerOperand();
// Conservatively require that the base pointer be fully dereferenceable.
// Conservatively require that the base pointer be fully dereferenceable
// and aligned.
if (!Visited.insert(Base).second)
return false;
if (!isDereferenceablePointer(Base, DL, CtxI,
DT, TLI, Visited))
if (!isDereferenceableAndAlignedPointer(Base, Align, DL, CtxI, DT, TLI,
Visited))
return false;
APInt Offset(DL.getPointerTypeSizeInBits(VTy), 0);
if (!GEP->accumulateConstantOffset(DL, Offset))
return false;
// Check if the load is within the bounds of the underlying object.
// Check if the load is within the bounds of the underlying object
// and offset is aligned.
uint64_t LoadSize = DL.getTypeStoreSize(Ty);
Type *BaseType = Base->getType()->getPointerElementType();
return (Offset + LoadSize).ule(DL.getTypeAllocSize(BaseType));
assert(isPowerOf2_32(Align) && "must be a power of 2!");
return (Offset + LoadSize).ule(DL.getTypeAllocSize(BaseType)) &&
!(Offset & APInt(Offset.getBitWidth(), Align-1));
}
// For gc.relocate, look through relocations
if (const IntrinsicInst *I = dyn_cast<IntrinsicInst>(V))
if (I->getIntrinsicID() == Intrinsic::experimental_gc_relocate) {
GCRelocateOperands RelocateInst(I);
return isDereferenceablePointer(RelocateInst.getDerivedPtr(), DL, CtxI,
DT, TLI, Visited);
return isDereferenceableAndAlignedPointer(
RelocateInst.getDerivedPtr(), Align, DL, CtxI, DT, TLI, Visited);
}
if (const AddrSpaceCastInst *ASC = dyn_cast<AddrSpaceCastInst>(V))
return isDereferenceablePointer(ASC->getOperand(0), DL, CtxI,
DT, TLI, Visited);
return isDereferenceableAndAlignedPointer(ASC->getOperand(0), Align, DL,
CtxI, DT, TLI, Visited);
// If we don't know, assume the worst.
return false;
}
bool llvm::isDereferenceablePointer(const Value *V, const DataLayout &DL,
const Instruction *CtxI,
const DominatorTree *DT,
const TargetLibraryInfo *TLI) {
bool llvm::isDereferenceableAndAlignedPointer(const Value *V, unsigned Align,
const DataLayout &DL,
const Instruction *CtxI,
const DominatorTree *DT,
const TargetLibraryInfo *TLI) {
// When dereferenceability information is provided by a dereferenceable
// attribute, we know exactly how many bytes are dereferenceable. If we can
// determine the exact offset to the attributed variable, we can use that
// information here.
Type *VTy = V->getType();
Type *Ty = VTy->getPointerElementType();
// Require ABI alignment for loads without alignment specification
if (Align == 0)
Align = DL.getABITypeAlignment(Ty);
if (Ty->isSized()) {
APInt Offset(DL.getTypeStoreSizeInBits(VTy), 0);
const Value *BV = V->stripAndAccumulateInBoundsConstantOffsets(DL, Offset);
if (Offset.isNonNegative())
if (isDereferenceableFromAttribute(BV, Offset, Ty, DL,
CtxI, DT, TLI))
if (isDereferenceableFromAttribute(BV, Offset, Ty, DL, CtxI, DT, TLI) &&
isAligned(BV, Offset, Align, DL))
return true;
}
SmallPtrSet<const Value *, 32> Visited;
return ::isDereferenceablePointer(V, DL, CtxI, DT, TLI, Visited);
return ::isDereferenceableAndAlignedPointer(V, Align, DL, CtxI, DT, TLI,
Visited);
}
bool llvm::isDereferenceablePointer(const Value *V, const DataLayout &DL,
const Instruction *CtxI,
const DominatorTree *DT,
const TargetLibraryInfo *TLI) {
return isDereferenceableAndAlignedPointer(V, 1, DL, CtxI, DT, TLI);
}
bool llvm::isSafeToSpeculativelyExecute(const Value *V,
@ -3092,7 +3135,8 @@ bool llvm::isSafeToSpeculativelyExecute(const Value *V,
LI->getParent()->getParent()->hasFnAttribute(Attribute::SanitizeThread))
return false;
const DataLayout &DL = LI->getModule()->getDataLayout();
return isDereferenceablePointer(LI->getPointerOperand(), DL, CtxI, DT, TLI);
return isDereferenceableAndAlignedPointer(
LI->getPointerOperand(), LI->getAlignment(), DL, CtxI, DT, TLI);
}
case Instruction::Call: {
if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {

70
llvm/test/Analysis/ValueTracking/memory-dereferenceable.ll
View File

@ -13,60 +13,104 @@ declare zeroext i1 @return_i1()
%struct.A = type { [8 x i8], [5 x i8] }
@globalstruct = external global %struct.A
define void @test(i32 addrspace(1)* dereferenceable(8) %dparam) gc "statepoint-example" {
@globalptr.align1 = external global i8, align 1
@globalptr.align16 = external global i8, align 16
define void @test(i32 addrspace(1)* dereferenceable(8) %dparam,
i8 addrspace(1)* dereferenceable(32) align 1 %dparam.align1,
i8 addrspace(1)* dereferenceable(32) align 16 %dparam.align16)
gc "statepoint-example" {
; CHECK: The following are dereferenceable:
; CHECK: %globalptr
; CHECK: %alloca
; CHECK: %dparam
; CHECK: %relocate
; CHECK-NOT: %nparam
; CHECK-NOT: %nd_load
; CHECK: %d4_load
; CHECK-NOT: %d2_load
; CHECK-NOT: %d_or_null_load
; CHECK: %d_or_null_non_null_load
; CHECK: %within_allocation
; CHECK-NOT: %outside_allocation
entry:
; CHECK: %globalptr{{.*}}(aligned)
%globalptr = getelementptr inbounds [6 x i8], [6 x i8]* @globalstr, i32 0, i32 0
%load1 = load i8, i8* %globalptr
; CHECK: %alloca{{.*}}(aligned)
%alloca = alloca i1
%load2 = load i1, i1* %alloca
; CHECK: %dparam{{.*}}(aligned)
%load3 = load i32, i32 addrspace(1)* %dparam
; CHECK: %relocate{{.*}}(aligned)
%tok = tail call i32 (i64, i32, i1 ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_i1f(i64 0, i32 0, i1 ()* @return_i1, i32 0, i32 0, i32 0, i32 0, i32 addrspace(1)* %dparam)
%relocate = call i32 addrspace(1)* @llvm.experimental.gc.relocate.p1i32(i32 %tok, i32 7, i32 7)
%load4 = load i32, i32 addrspace(1)* %relocate
; CHECK-NOT: %nparam
%nparam = getelementptr i32, i32 addrspace(1)* %dparam, i32 5
%load5 = load i32, i32 addrspace(1)* %nparam
; Load from a non-dereferenceable load
; CHECK-NOT: %nd_load
%nd_load = load i32*, i32** @globali32ptr
%load6 = load i32, i32* %nd_load
; Load from a dereferenceable load
; CHECK: %d4_load{{.*}}(aligned)
%d4_load = load i32*, i32** @globali32ptr, !dereferenceable !0
%load7 = load i32, i32* %d4_load
; Load from an offset not covered by the dereferenceable portion
; CHECK-NOT: %d2_load
%d2_load = load i32*, i32** @globali32ptr, !dereferenceable !1
%load8 = load i32, i32* %d2_load
; Load from a potentially null pointer with dereferenceable_or_null
; CHECK-NOT: %d_or_null_load
%d_or_null_load = load i32*, i32** @globali32ptr, !dereferenceable_or_null !0
%load9 = load i32, i32* %d_or_null_load
; Load from a non-null pointer with dereferenceable_or_null
; CHECK: %d_or_null_non_null_load{{.*}}(aligned)
%d_or_null_non_null_load = load i32*, i32** @globali32ptr, !nonnull !2, !dereferenceable_or_null !0
%load10 = load i32, i32* %d_or_null_non_null_load
; It's OK to overrun static array size as long as we stay within underlying object size
; CHECK: %within_allocation{{.*}}(aligned)
%within_allocation = getelementptr inbounds %struct.A, %struct.A* @globalstruct, i64 0, i32 0, i64 10
%load11 = load i8, i8* %within_allocation
; GEP is outside the underlying object size
; CHECK-NOT: %outside_allocation
%outside_allocation = getelementptr inbounds %struct.A, %struct.A* @globalstruct, i64 0, i32 1, i64 10
%load12 = load i8, i8* %outside_allocation
; Loads from aligned globals
; CHECK: @globalptr.align1{{.*}}(unaligned)
; CHECK: @globalptr.align16{{.*}}(aligned)
%load13 = load i8, i8* @globalptr.align1, align 16
%load14 = load i8, i8* @globalptr.align16, align 16
; Loads from aligned arguments
; CHECK: %dparam.align1{{.*}}(unaligned)
; CHECK: %dparam.align16{{.*}}(aligned)
%load15 = load i8, i8 addrspace(1)* %dparam.align1, align 16
%load16 = load i8, i8 addrspace(1)* %dparam.align16, align 16
; Loads from aligned allocas
; CHECK: %alloca.align1{{.*}}(unaligned)
; CHECK: %alloca.align16{{.*}}(aligned)
%alloca.align1 = alloca i1, align 1
%alloca.align16 = alloca i1, align 16
%load17 = load i1, i1* %alloca.align1, align 16
%load18 = load i1, i1* %alloca.align16, align 16
; Loads from GEPs
; CHECK: %gep.align1.offset1{{.*}}(unaligned)
; CHECK: %gep.align16.offset1{{.*}}(unaligned)
; CHECK: %gep.align1.offset16{{.*}}(unaligned)
; CHECK: %gep.align16.offset16{{.*}}(aligned)
%gep.align1.offset1 = getelementptr inbounds i8, i8 addrspace(1)* %dparam.align1, i32 1
%gep.align16.offset1 = getelementptr inbounds i8, i8 addrspace(1)* %dparam.align16, i32 1
%gep.align1.offset16 = getelementptr inbounds i8, i8 addrspace(1)* %dparam.align1, i32 16
%gep.align16.offset16 = getelementptr inbounds i8, i8 addrspace(1)* %dparam.align16, i32 16
%load19 = load i8, i8 addrspace(1)* %gep.align1.offset1, align 16
%load20 = load i8, i8 addrspace(1)* %gep.align16.offset1, align 16
%load21 = load i8, i8 addrspace(1)* %gep.align1.offset16, align 16
%load22 = load i8, i8 addrspace(1)* %gep.align16.offset16, align 16
ret void
}