Add support for nested symbol references.

This change allows for adding additional nested references to a SymbolRefAttr to allow for further resolving a symbol if that symbol also defines a SymbolTable. If a referenced symbol also defines a symbol table, a nested reference can be used to refer to a symbol within that table. Nested references are printed after the main reference in the following form:

  symbol-ref-attribute ::= symbol-ref-id (`::` symbol-ref-id)*

Example:

  module @reference {
    func @nested_reference()
  }

  my_reference_op @reference::@nested_reference

Given that SymbolRefAttr is now more general, the existing functionality centered around a single reference is moved to a derived class FlatSymbolRefAttr. Followup commits will add support to lookups, rauw, etc. for scoped references.

PiperOrigin-RevId: 279860501

2 files changed, 4 insertions, 2 deletions

diff --git a/mlir/lib/Dialect/GPU/IR/GPUDialect.cpp b/mlir/lib/Dialect/GPU/IR/GPUDialect.cpp
index d70d51feee7..bfd094d6203 100644
--- a/mlir/lib/Dialect/GPU/IR/GPUDialect.cpp
+++ b/mlir/lib/Dialect/GPU/IR/GPUDialect.cpp
@@ -533,7 +533,8 @@ unsigned LaunchFuncOp::getNumKernelOperands() {
 }
 
 StringRef LaunchFuncOp::getKernelModuleName() {
-  return getAttrOfType<SymbolRefAttr>(getKernelModuleAttrName()).getValue();
+  return getAttrOfType<SymbolRefAttr>(getKernelModuleAttrName())
+      .getRootReference();
 }
 
 Value *LaunchFuncOp::getKernelOperand(unsigned i) {
diff --git a/mlir/lib/Dialect/GPU/Transforms/KernelOutlining.cpp b/mlir/lib/Dialect/GPU/Transforms/KernelOutlining.cpp
index 672beee56cd..420b2340bc9 100644
--- a/mlir/lib/Dialect/GPU/Transforms/KernelOutlining.cpp
+++ b/mlir/lib/Dialect/GPU/Transforms/KernelOutlining.cpp
@@ -189,7 +189,8 @@ private:
       if (Optional<SymbolTable::UseRange> symbolUses =
               SymbolTable::getSymbolUses(symbolDefWorklist.pop_back_val())) {
         for (SymbolTable::SymbolUse symbolUse : *symbolUses) {
-          StringRef symbolName = symbolUse.getSymbolRef().getValue();
+          StringRef symbolName =
+              symbolUse.getSymbolRef().cast<FlatSymbolRefAttr>().getValue();
           if (moduleManager.lookupSymbol(symbolName))
             continue;