InstCombine: propagate deref via new addDereferenceableAttr

[artagnon]

Summary

The "dereferenceable" attribute cannot be added via .addAttribute(),
since it also expects a size in bytes. AttrBuilder#addAttribute or
AttributeSet#addAttribute is wrapped by classes Function, InvokeInst,
and CallInst. Add corresponding wrappers to
AttrBuilder#addDereferenceableAttr.

Having done this, propagate the dereferenceable attribute via
gc.relocate, adding a test to exercise it. Note that -datalayout is
required during execution over and above -instcombine, because
InstCombine only optionally requires DataLayoutPass.

[reames]

General direction seems fine. I can't comment on the attribute set stuff (I've never taken the time to understand it), maybe Hal can?

lib/Transforms/InstCombine/InstCombineCalls.cpp

1139

This cast is not safe. Dereferencabble pointers can come from other sources (e.g. calls) as well.

[artagnon]

Don't assume that the derived pointer can always be cast to an
Argument; dyn_cast and check.

[reames]

GC parts LGTM; explicitly not addressing attribute changes

p.s. isDerefPtr is on Value, the cast is entirely unnecessary.

[artagnon]

In D7510#120855, @reames wrote:

p.s. isDerefPtr is on Value, the cast is entirely unnecessary.

Ah, but ->getDereferenceableBytes() is only defined for an Argument; I'm not sure why it is that way though.

[reames]

In D7510#120890, @artagnon wrote:

In D7510#120855, @reames wrote:

p.s. isDerefPtr is on Value, the cast is entirely unnecessary.

Ah, but ->getDereferenceableBytes() is only defined for an Argument; I'm not sure why it is that way though.

Ok, I see why you need the cast. Another idea for later cleanup. :)

[hfinkel]

The changes adding addDereferenceableAttr functions LGTM, so I think you're good to go.

include/llvm/IR/Attributes.h

AttributeSet removeAttribute(LLVMContext &C, unsigned Index,
                                Attribute::AttrKind Attr) const;
 
   /// \brief Remove the specified attributes at the specified index from this
   /// attribute list. Since attribute lists are immutable, this returns the new
   /// list.
   AttributeSet removeAttributes(LLVMContext &C, unsigned Index, 
                                 AttributeSet Attrs) const;
 
+  /// \brief Add the dereferenceable attribute to the attribute set at the given
+  /// index. Since attribute sets are immutable, this returns a new set.
+  AttributeSet addDereferenceableAttr(LLVMContext &C, unsigned Index,
+                                      uint64_t Bytes) const;
+
   //===--------------------------------------------------------------------===//
   // AttributeSet Accessors
   //===--------------------------------------------------------------------===//
 
   /// \brief Retrieve the LLVM context.
   LLVMContext &getContext() const;
 
   /// \brief The attributes for the specified index are returned.

include/llvm/IR/Function.h

public:
   void addAttribute(unsigned i, Attribute::AttrKind attr);
 
   /// @brief adds the attributes to the list of attributes.
   void addAttributes(unsigned i, AttributeSet attrs);
 
   /// @brief removes the attributes from the list of attributes.
   void removeAttributes(unsigned i, AttributeSet attr);
 
+  /// @brief adds the dereferenceable attribute to the list of attributes.
+  void addDereferenceableAttr(unsigned i, uint64_t Bytes);
+
   /// @brief Extract the alignment for a call or parameter (0=unknown).
   unsigned getParamAlignment(unsigned i) const {
     return AttributeSets.getParamAlignment(i);
   }
 
   /// @brief Extract the number of dereferenceable bytes for a call or
   /// parameter (0=unknown).
   uint64_t getDereferenceableBytes(unsigned i) const {

include/llvm/IR/Instructions.h

public:
   void setAttributes(const AttributeSet &Attrs) { AttributeList = Attrs; }
 
   /// addAttribute - adds the attribute to the list of attributes.
   void addAttribute(unsigned i, Attribute::AttrKind attr);
 
   /// removeAttribute - removes the attribute from the list of attributes.
   void removeAttribute(unsigned i, Attribute attr);
 
+  /// \brief adds the dereferenceable attribute to the list of attributes.
+  void addDereferenceableAttr(unsigned i, uint64_t Bytes);
+
   /// \brief Determine whether this call has the given attribute.
   bool hasFnAttr(Attribute::AttrKind A) const {
     assert(A != Attribute::NoBuiltin &&
            "Use CallInst::isNoBuiltin() to check for Attribute::NoBuiltin");
     return hasFnAttrImpl(A);
   }
 
   /// \brief Determine whether the call or the callee has the given attributes.
public:
   void setAttributes(const AttributeSet &Attrs) { AttributeList = Attrs; }
 
   /// addAttribute - adds the attribute to the list of attributes.
   void addAttribute(unsigned i, Attribute::AttrKind attr);
 
   /// removeAttribute - removes the attribute from the list of attributes.
   void removeAttribute(unsigned i, Attribute attr);
 
+  /// \brief removes the dereferenceable attribute to the list of attributes.
+  void addDereferenceableAttr(unsigned i, uint64_t Bytes);
+
   /// \brief Determine whether this call has the given attribute.
   bool hasFnAttr(Attribute::AttrKind A) const {
     assert(A != Attribute::NoBuiltin &&
            "Use CallInst::isNoBuiltin() to check for Attribute::NoBuiltin");
     return hasFnAttrImpl(A);
   }
 
   /// \brief Determine whether the call or the callee has the given attributes.

lib/IR/Attributes.cpp

#endif
 
   // Add the remaining attribute slots.
   for (unsigned I = LastIndex, E = NumAttrs; I < E; ++I)
     AttrSet.push_back(getSlotAttributes(I));
 
   return get(C, AttrSet);
 }
 
+AttributeSet AttributeSet::addDereferenceableAttr(LLVMContext &C, unsigned Index,
+                                                  uint64_t Bytes) const {
+  llvm::AttrBuilder B;
+  B.addDereferenceableAttr(Bytes);
+  return addAttributes(C, Index, AttributeSet::get(C, Index, B));
+}
+
 //===----------------------------------------------------------------------===//
 // AttributeSet Accessor Methods
 //===----------------------------------------------------------------------===//
 
 LLVMContext &AttributeSet::getContext() const {
   return pImpl->getContext();
 }
 

lib/IR/Function.cpp

 }
 
 void Function::removeAttributes(unsigned i, AttributeSet attrs) {
   AttributeSet PAL = getAttributes();
   PAL = PAL.removeAttributes(getContext(), i, attrs);
   setAttributes(PAL);
 }
 
+void Function::addDereferenceableAttr(unsigned i, uint64_t Bytes) {
+  AttributeSet PAL = getAttributes();
+  PAL = PAL.addDereferenceableAttr(getContext(), i, Bytes);
+  setAttributes(PAL);
+}
+
 // Maintain the GC name for each function in an on-the-side table. This saves
 // allocating an additional word in Function for programs which do not use GC
 // (i.e., most programs) at the cost of increased overhead for clients which do
 // use GC.
 static DenseMap<const Function*,PooledStringPtr> *GCNames;
 static StringPool *GCNamePool;
 static ManagedStatic<sys::SmartRWMutex<true> > GCLock;
 

lib/IR/Instructions.cpp

void CallInst::removeAttribute(unsigned i, Attribute attr) {
   AttributeSet PAL = getAttributes();
   AttrBuilder B(attr);
   LLVMContext &Context = getContext();
   PAL = PAL.removeAttributes(Context, i,
                              AttributeSet::get(Context, i, B));
   setAttributes(PAL);
 }
 
+void CallInst::addDereferenceableAttr(unsigned i, uint64_t Bytes) {
+  AttributeSet PAL = getAttributes();
+  PAL = PAL.addDereferenceableAttr(getContext(), i, Bytes);
+  setAttributes(PAL);
+}
+
 bool CallInst::hasFnAttrImpl(Attribute::AttrKind A) const {
   if (AttributeList.hasAttribute(AttributeSet::FunctionIndex, A))
     return true;
   if (const Function *F = getCalledFunction())
     return F->getAttributes().hasAttribute(AttributeSet::FunctionIndex, A);
   return false;
 }
 

 void InvokeInst::removeAttribute(unsigned i, Attribute attr) {
   AttributeSet PAL = getAttributes();
   AttrBuilder B(attr);
   PAL = PAL.removeAttributes(getContext(), i,
                              AttributeSet::get(getContext(), i, B));
   setAttributes(PAL);
 }
 
+void InvokeInst::addDereferenceableAttr(unsigned i, uint64_t Bytes) {
+  AttributeSet PAL = getAttributes();
+  PAL = PAL.addDereferenceableAttr(getContext(), i, Bytes);
+  setAttributes(PAL);
+}
+
 LandingPadInst *InvokeInst::getLandingPadInst() const {
   return cast<LandingPadInst>(getUnwindDest()->getFirstNonPHI());
 }
 
 //===----------------------------------------------------------------------===//
 //                        ReturnInst Implementation
 //===----------------------------------------------------------------------===//
 

lib/Transforms/InstCombine/InstCombineCalls.cpp

case Intrinsic::experimental_gc_relocate: {
     // collector this property does not hold for.
     if (isa<ConstantPointerNull>(DerivedPtr))
       return ReplaceInstUsesWith(*II, DerivedPtr);
 
     // isKnownNonNull -> nonnull attribute
     if (isKnownNonNull(DerivedPtr))
       II->addAttribute(AttributeSet::ReturnIndex, Attribute::NonNull);
 
-    // TODO: dereferenceable -> deref attribute
+    // isDereferenceablePointer -> deref attribute
+    if (DerivedPtr->isDereferenceablePointer(DL)) {
+      if (Argument *A = dyn_cast<Argument>(DerivedPtr)) {
+        uint64_t Bytes = A->getDereferenceableBytes();
+        II->addDereferenceableAttr(AttributeSet::ReturnIndex, Bytes);
+      }
+    }
 
     // TODO: bitcast(relocate(p)) -> relocate(bitcast(p))
     // Canonicalize on the type from the uses to the defs
-    
     // TODO: relocate((gep p, C, C2, ...)) -> gep(relocate(p), C, C2, ...)
   }
   }
 
   return visitCallSite(II);
 }
 
 // InvokeInst simplification

test/Transforms/InstCombine/gc.relocate.ll

+; RUN: opt < %s -datalayout -instcombine -S | FileCheck %s
+
+; Uses InstCombine with DataLayout to propagate dereferenceable
+; attribute via gc.relocate: if the derived ptr is dereferenceable(N),
+; then the return attribute of gc.relocate is dereferenceable(N).
+
+declare zeroext i1 @return_i1()
+declare i32 @llvm.experimental.gc.statepoint.p0f_i1f(i1 ()*, i32, i32, ...)
+declare i32 addrspace(1)* @llvm.experimental.gc.relocate.p1i32(i32, i32, i32)
+
+define i32 addrspace(1)* @deref(i32 addrspace(1)* dereferenceable(8) %dparam) {
+; Checks that a dereferenceabler pointer
+; CHECK-LABEL: @deref
+; CHECK: call dereferenceable(8)
+entry:
+    %load = load i32 addrspace(1)* %dparam
+    %tok = tail call i32 (i1 ()*, i32, i32, ...)* @llvm.experimental.gc.statepoint.p0f_i1f(i1 ()* @return_i1, i32 0, i32 0, i32 0, i32 addrspace(1)* %dparam)
+    %relocate = call i32 addrspace(1)* @llvm.experimental.gc.relocate.p1i32(i32 %tok, i32 4, i32 4)
+    ret i32 addrspace(1)* %relocate
+}
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