[mlir][transforms] Skip RemoveDeadValues for function declaration (#108221)

This patch skips `RemoveDeadValues` if funcOp is declaration, which
fixes a crash.
Fixes #107546.

Author: CoTinker

mlir/lib/Transforms/RemoveDeadValues.cpp

@@ -191,10 +191,10 @@ static void cleanSimpleOp(Operation *op, RunLivenessAnalysis &la) {
 ///   non-live across all callers),
 ///   (5) Dropping the uses of these return values from its callers, AND
 ///   (6) Erasing these return values
-/// iff it is not public.
+/// iff it is not public or declaration.
 static void cleanFuncOp(FunctionOpInterface funcOp, Operation *module,
                         RunLivenessAnalysis &la) {
-  if (funcOp.isPublic())
+  if (funcOp.isPublic() || funcOp.isDeclaration())
     return;
 
   // Get the list of unnecessary (non-live) arguments in `nonLiveArgs`.

mlir/test/Transforms/remove-dead-values.mlir

@@ -357,3 +357,8 @@ func.func @kernel(%arg0: memref<18xf32>) {
 // CHECK: gpu.launch blocks
 // CHECK: memref.store
 // CHECK-NEXT: gpu.terminator
+
+// -----
+
+// CHECK: func.func private @no_block_func_declaration()
+func.func private @no_block_func_declaration() -> ()