Add a dereferenceable attribute

This attribute indicates that the parameter or return pointer is
dereferenceable. Practically speaking, loads from such a pointer within the
associated byte range are safe to speculatively execute. Such pointer
parameters are common in source languages (C++ references, for example).

llvm-svn: 213385

1 files changed, 15 insertions, 3 deletions

diff --git a/llvm/lib/IR/Function.cpp b/llvm/lib/IR/Function.cpp
index 1443571..de59b26e 100644
--- a/llvm/lib/IR/Function.cpp
+++ b/llvm/lib/IR/Function.cpp
@@ -77,11 +77,17 @@ unsigned Argument::getArgNo() const {
 }
 
 /// hasNonNullAttr - Return true if this argument has the nonnull attribute on
-/// it in its containing function.
+/// it in its containing function. Also returns true if at least one byte is
+/// known to be dereferenceable and the pointer is in addrspace(0).
 bool Argument::hasNonNullAttr() const {
   if (!getType()->isPointerTy()) return false;
-  return getParent()->getAttributes().
-    hasAttribute(getArgNo()+1, Attribute::NonNull);
+  if (getParent()->getAttributes().
+        hasAttribute(getArgNo()+1, Attribute::NonNull))
+    return true;
+  else if (getDereferenceableBytes() > 0 &&
+           getType()->getPointerAddressSpace() == 0)
+    return true;
+  return false;
 }
 
 /// hasByValAttr - Return true if this argument has the byval attribute on it
@@ -113,6 +119,12 @@ unsigned Argument::getParamAlignment() const {
 
 }
 
+uint64_t Argument::getDereferenceableBytes() const {
+  assert(getType()->isPointerTy() &&
+         "Only pointers have dereferenceable bytes");
+  return getParent()->getDereferenceableBytes(getArgNo()+1);
+}
+
 /// hasNestAttr - Return true if this argument has the nest attribute on
 /// it in its containing function.
 bool Argument::hasNestAttr() const {