AMDGPU: Fix private handling for allowsMisalignedMemoryAccesses

If the alignment is at least 4, this should report true.

Something still seems off with how < 4-byte types are
handled here though.

Fixing this seems to change how some combines get
to where they get, but somehow isn't changing the net
result.

llvm-svn: 342879
diff --git a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
index 3de6a54..1bc430b 100644
--- a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
@@ -1069,7 +1069,11 @@
   if (!Subtarget->hasUnalignedScratchAccess() &&
       (AddrSpace == AMDGPUAS::PRIVATE_ADDRESS ||
        AddrSpace == AMDGPUAS::FLAT_ADDRESS)) {
-    return false;
+    bool AlignedBy4 = Align >= 4;
+    if (IsFast)
+      *IsFast = AlignedBy4;
+
+    return AlignedBy4;
   }
 
   if (Subtarget->hasUnalignedBufferAccess()) {