Fix Bug in RemoveDeadValues Pass (#148437)

This patch fixes a bug in the RemoveDeadValues pass where unused
function arguments were not removed from the function signature in an
edge case where the function returns void.
A corresponding test was added to the MLIR LIT test suite to cover this
case.

Author: ronigoldman22

mlir/lib/Transforms/RemoveDeadValues.cpp

@@ -345,8 +345,6 @@ static void processFuncOp(FunctionOpInterface funcOp, Operation *module,
   // since it forwards only to non-live value(s) (%1#1).
   Operation *lastReturnOp = funcOp.back().getTerminator();
   size_t numReturns = lastReturnOp->getNumOperands();
-  if (numReturns == 0)
-    return;
   BitVector nonLiveRets(numReturns, true);
   for (SymbolTable::SymbolUse use : uses) {
     Operation *callOp = use.getUser();
@@ -368,6 +366,8 @@ static void processFuncOp(FunctionOpInterface funcOp, Operation *module,
   cl.functions.push_back({funcOp, nonLiveArgs, nonLiveRets});
 
   // Do (5) and (6).
+  if (numReturns == 0)
+    return;
   for (SymbolTable::SymbolUse use : uses) {
     Operation *callOp = use.getUser();
     assert(isa<CallOpInterface>(callOp) && "expected a call-like user");

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

@@ -548,3 +548,26 @@ func.func @test_atomic_yield(%I: memref<10xf32>, %idx : index) {
   func.return
 }
 
+// -----
+
+// CHECK-LABEL: module @return_void_with_unused_argument
+module @return_void_with_unused_argument {
+  // CHECK-LABEL: func.func private @fn_return_void_with_unused_argument
+  // CHECK-SAME: (%[[ARG0_FN:.*]]: i32)
+  func.func private @fn_return_void_with_unused_argument(%arg0: i32, %arg1: memref<4xi32>) -> () {
+    %sum = arith.addi %arg0, %arg0 : i32
+    %c0 = arith.constant 0 : index
+    %buf = memref.alloc() : memref<1xi32>
+    memref.store %sum, %buf[%c0] : memref<1xi32>
+    return
+  }
+  // CHECK-LABEL: func.func @main
+  // CHECK-SAME: (%[[ARG0_MAIN:.*]]: i32)
+  // CHECK: call @fn_return_void_with_unused_argument(%[[ARG0_MAIN]]) : (i32) -> ()
+  func.func @main(%arg0: i32) -> memref<4xi32> {
+    %unused = memref.alloc() : memref<4xi32>
+    call @fn_return_void_with_unused_argument(%arg0, %unused) : (i32, memref<4xi32>) -> ()
+    return %unused : memref<4xi32>
+  }
+}
+