[SelectionDAG] set dereferenceable flag when expanding memcpy/memmove

When SelectionDAG expands memcpy (or memmove) call into a sequence of load and store instructions, it disregards dereferenceable flag even the source pointer is known to be dereferenceable.
This results in an assertion failure if SelectionDAG commonizes a load instruction generated for memcpy with another load instruction for the source pointer.
This patch makes SelectionDAG to set the dereferenceable flag for the load instructions properly to avoid the assertion failure.

Differential Revision: https://reviews.llvm.org/D34467

llvm-svn: 306209

1 files changed, 18 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineInstr.cpp b/llvm/lib/CodeGen/MachineInstr.cpp
index 2a6cb07d..81c6dac 100644
--- a/llvm/lib/CodeGen/MachineInstr.cpp
+++ b/llvm/lib/CodeGen/MachineInstr.cpp
@@ -21,6 +21,7 @@
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/Loads.h"
 #include "llvm/Analysis/MemoryLocation.h"
 #include "llvm/CodeGen/GlobalISel/RegisterBank.h"
 #include "llvm/CodeGen/MachineBasicBlock.h"
@@ -558,6 +559,23 @@ unsigned MachinePointerInfo::getAddrSpace() const {
   return cast<PointerType>(V.get<const Value*>()->getType())->getAddressSpace();
 }
 
+/// isDereferenceable - Return true if V is always dereferenceable for 
+/// Offset + Size byte.
+bool MachinePointerInfo::isDereferenceable(unsigned Size, LLVMContext &C,
+                                           const DataLayout &DL) const {
+  if (!V.is<const Value*>())
+    return false;
+
+  const Value *BasePtr = V.get<const Value*>();
+  if (BasePtr == nullptr)
+    return false;
+
+  return isDereferenceableAndAlignedPointer(BasePtr, 1,
+                                            APInt(DL.getPointerSize(),
+                                                  Offset + Size),
+                                            DL);
+}
+
 /// getConstantPool - Return a MachinePointerInfo record that refers to the
 /// constant pool.
 MachinePointerInfo MachinePointerInfo::getConstantPool(MachineFunction &MF) {