[mlir] Retain metadata for single loc fusedloc

If a fusedloc is created with a single location then no fusedloc
was previously created and single location returned instead. In the case
where there is a metadata associated with the location this results in
discarding the metadata. Instead only canonicalize where there is no
loss of information.

Differential Revision: https://reviews.llvm.org/D115605

mlir/lib/Bindings/Python/IRCore.cpp

@@ -2363,8 +2363,6 @@ void mlir::python::populateIRCore(py::module &m) {
           [](const std::vector<PyLocation> &pyLocations,
              llvm::Optional<PyAttribute> metadata,
              DefaultingPyMlirContext context) {
-            if (pyLocations.empty())
-              throw py::value_error("No locations provided");
             llvm::SmallVector<MlirLocation, 4> locations;
             locations.reserve(pyLocations.size());
             for (auto &pyLocation : pyLocations)

mlir/lib/IR/Location.cpp

@@ -106,10 +106,18 @@ Location FusedLoc::get(ArrayRef<Location> locs, Attribute metadata,
   }
   locs = decomposedLocs.getArrayRef();
 
-  // Handle the simple cases of less than two locations.
-  if (locs.empty())
-    return UnknownLoc::get(context);
-  if (locs.size() == 1)
+  // Handle the simple cases of less than two locations. Ensure the metadata (if
+  // provided) is not dropped.
+  if (locs.empty()) {
+    if (!metadata)
+      return UnknownLoc::get(context);
+    // TODO: Investigate ASAN failure when using implicit conversion from
+    // Location to ArrayRef<Location> below.
+    return Base::get(context, ArrayRef<Location>{UnknownLoc::get(context)},
+                     metadata);
+  }
+  if (locs.size() == 1 && !metadata)
     return locs.front();
+
   return Base::get(context, locs, metadata);
 }

mlir/test/IR/locations.mlir

@@ -21,6 +21,10 @@ func @inline_notation() -> i32 {
   affine.if #set0(%2) {
   } loc(fused<"myPass">["foo", "foo2"])
 
+  // CHECK: } loc(fused<"myPass">["foo"])
+  affine.if #set0(%2) {
+  } loc(fused<"myPass">["foo"])
+
   // CHECK: return %0 : i32 loc(unknown)
   return %1 : i32 loc(unknown)
 }

mlir/test/python/ir/location.py

@@ -78,12 +78,20 @@ def testCallSite():
 # CHECK-LABEL: TEST: testFused
 def testFused():
   with Context() as ctx:
+    loc_single = Location.fused([Location.name("apple")])
     loc = Location.fused(
         [Location.name("apple"), Location.name("banana")])
     attr = Attribute.parse('"sauteed"')
     loc_attr = Location.fused([Location.name("carrot"),
                                Location.name("potatoes")], attr)
+    loc_empty = Location.fused([])
+    loc_empty_attr = Location.fused([], attr)
+    loc_single_attr = Location.fused([Location.name("apple")], attr)
   ctx = None
+  # CHECK: file str: loc("apple")
+  print("file str:", str(loc_single))
+  # CHECK: file repr: loc("apple")
+  print("file repr:", repr(loc_single))
   # CHECK: file str: loc(fused["apple", "banana"])
   print("file str:", str(loc))
   # CHECK: file repr: loc(fused["apple", "banana"])
@@ -92,6 +100,18 @@ def testFused():
   print("file str:", str(loc_attr))
   # CHECK: file repr: loc(fused<"sauteed">["carrot", "potatoes"])
   print("file repr:", repr(loc_attr))
+  # CHECK: file str: loc(unknown)
+  print("file str:", str(loc_empty))
+  # CHECK: file repr: loc(unknown)
+  print("file repr:", repr(loc_empty))
+  # CHECK: file str: loc(fused<"sauteed">[unknown])
+  print("file str:", str(loc_empty_attr))
+  # CHECK: file repr: loc(fused<"sauteed">[unknown])
+  print("file repr:", repr(loc_empty_attr))
+  # CHECK: file str: loc(fused<"sauteed">["apple"])
+  print("file str:", str(loc_single_attr))
+  # CHECK: file repr: loc(fused<"sauteed">["apple"])
+  print("file repr:", repr(loc_single_attr))
 
 run(testFused)