[PATCH] D17611: NFC. Introduce Value::isPointerDereferenceable

[Artur Pilipenko via llvm-commits]

apilipenko created this revision.
apilipenko added reviewers: hfinkel, reames.
apilipenko added a subscriber: llvm-commits.

This is analogous to D17572 (and the diff is based upon it). Extract a part of isDereferenceableAndAlignedPointer functionality to Value::isPointerDereferenceable. The difference between those function is that isPointerDereferenceable can be used for opaque types.

http://reviews.llvm.org/D17611

Files:
  include/llvm/IR/Value.h
  lib/Analysis/Loads.cpp
  lib/IR/Value.cpp

Index: lib/IR/Value.cpp
===================================================================
--- lib/IR/Value.cpp
+++ lib/IR/Value.cpp
@@ -553,6 +553,29 @@
   return DerefBytes;
 }
 
+bool Value::isPointerDereferenceable(bool &CanBeNull) const {
+  assert(getType()->isPointerTy() && "must be pointer");
+
+  CanBeNull = false;
+
+  // These are obviously ok.
+  if (isa<AllocaInst>(this))
+    return true;
+
+  // Global variables which can't collapse to null are ok.
+  // TODO: return true for those but set CanBeNull flag
+  if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(this))
+    if (!GV->hasExternalWeakLinkage())
+      return true;
+
+  // byval arguments are okay.
+  if (const Argument *A = dyn_cast<Argument>(this))
+    if (A->hasByValAttr())
+      return true;
+
+  return false;
+}
+
 unsigned Value::getPointerAlignment(const DataLayout &DL) const {
   assert(getType()->isPointerTy() && "must be pointer");
 
Index: lib/Analysis/Loads.cpp
===================================================================
--- lib/Analysis/Loads.cpp
+++ lib/Analysis/Loads.cpp
@@ -91,9 +91,11 @@
   // Note that it is not safe to speculate into a malloc'd region because
   // malloc may return null.
 
-  // These are obviously ok if aligned.
-  if (isa<AllocaInst>(V))
+  bool CheckForNull;
+  if (V->isPointerDereferenceable(CheckForNull)) {
+    assert(!CheckForNull && "don't check for non-null currently");
     return isAligned(V, Align, DL);
+  }
 
   // It's not always safe to follow a bitcast, for example:
   //   bitcast i8* (alloca i8) to i32*
@@ -112,16 +114,6 @@
                                                 CtxI, DT, TLI, Visited);
   }
 
-  // Global variables which can't collapse to null are ok.
-  if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
-    if (!GV->hasExternalWeakLinkage())
-      return isAligned(V, Align, DL);
-
-  // byval arguments are okay.
-  if (const Argument *A = dyn_cast<Argument>(V))
-    if (A->hasByValAttr())
-      return isAligned(V, Align, DL);
-
   if (isDereferenceableFromAttribute(V, DL, CtxI, DT, TLI))
     return isAligned(V, Align, DL);
 
Index: include/llvm/IR/Value.h
===================================================================
--- include/llvm/IR/Value.h
+++ include/llvm/IR/Value.h
@@ -508,6 +508,12 @@
   /// dereferenceable up to the returned number of bytes.
   unsigned getPointerDereferenceableBytes(bool &CanBeNull) const;
 
+  /// \brief Returns true if the pointer value is fully dereferenceable.
+  ///
+  /// Sets CanBeNull to true if the pointer is either null or can be fully
+  /// dereferenceable.
+  bool isPointerDereferenceable(bool &CanBeNull) const;
+
   /// \brief Returns an alignment of the pointer value.
   ///
   /// Returns an alignment which is either specified explicitly, e.g. via


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