[IR] Introduce a dereferenceable_or_null(N) attribute.
Summary:
If a pointer is marked as dereferenceable_or_null(N), LLVM assumes it
is either `null` or `dereferenceable(N)` or both. This change only
introduces the attribute and adds a token test case for the `llvm-as`
/ `llvm-dis`. It does not hook up other parts of the optimizer to
actually exploit the attribute -- those changes will come later.
For pointers in address space 0, `dereferenceable(N)` is now exactly
equivalent to `dereferenceable_or_null(N)` && `nonnull`. For other
address spaces, `dereferenceable(N)` is potentially weaker than
`dereferenceable_or_null(N)` && `nonnull` (since we could have a null
`dereferenceable(N)` pointer).
The motivating case for this change is Java (and other managed
languages), where pointers are either `null` or dereferenceable up to
some usually known-at-compile-time constant offset.
Reviewers: rafael, hfinkel
Reviewed By: hfinkel
Subscribers: nicholas, llvm-commits
Differential Revision: http://reviews.llvm.org/D8650
llvm-svn: 235132
diff --git a/llvm/lib/IR/Instructions.cpp b/llvm/lib/IR/Instructions.cpp
index 8e3ddaa..85b7521 100644
--- a/llvm/lib/IR/Instructions.cpp
+++ b/llvm/lib/IR/Instructions.cpp
@@ -352,6 +352,12 @@
setAttributes(PAL);
}
+void CallInst::addDereferenceableOrNullAttr(unsigned i, uint64_t Bytes) {
+ AttributeSet PAL = getAttributes();
+ PAL = PAL.addDereferenceableOrNullAttr(getContext(), i, Bytes);
+ setAttributes(PAL);
+}
+
bool CallInst::hasFnAttrImpl(Attribute::AttrKind A) const {
if (AttributeList.hasAttribute(AttributeSet::FunctionIndex, A))
return true;
@@ -617,6 +623,12 @@
setAttributes(PAL);
}
+void InvokeInst::addDereferenceableOrNullAttr(unsigned i, uint64_t Bytes) {
+ AttributeSet PAL = getAttributes();
+ PAL = PAL.addDereferenceableOrNullAttr(getContext(), i, Bytes);
+ setAttributes(PAL);
+}
+
LandingPadInst *InvokeInst::getLandingPadInst() const {
return cast<LandingPadInst>(getUnwindDest()->getFirstNonPHI());
}