diff --git a/flang/lib/Optimizer/CodeGen/PreCGRewrite.cpp b/flang/lib/Optimizer/CodeGen/PreCGRewrite.cpp
index 044c2e775a6a7..a45fed2a36798 100644
--- a/flang/lib/Optimizer/CodeGen/PreCGRewrite.cpp
+++ b/flang/lib/Optimizer/CodeGen/PreCGRewrite.cpp
@@ -19,6 +19,7 @@
 #include "flang/Optimizer/Dialect/FIRType.h"
 #include "flang/Optimizer/Support/FIRContext.h"
 #include "mlir/Transforms/DialectConversion.h"
+#include "mlir/Transforms/RegionUtils.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/Debug.h"
 
@@ -284,7 +285,6 @@ class CodeGenRewrite : public fir::impl::CodeGenRewriteBase<CodeGenRewrite> {
 public:
   void runOn(mlir::Operation *op, mlir::Region &region) {
     auto &context = getContext();
-    mlir::OpBuilder rewriter(&context);
     mlir::ConversionTarget target(context);
     target.addLegalDialect<mlir::arith::ArithDialect, fir::FIROpsDialect,
                            fir::FIRCodeGenDialect, mlir::func::FuncDialect>();
@@ -305,9 +305,11 @@ class CodeGenRewrite : public fir::impl::CodeGenRewriteBase<CodeGenRewrite> {
       mlir::emitError(mlir::UnknownLoc::get(&context),
                       "error in running the pre-codegen conversions");
       signalPassFailure();
+      return;
     }
-    // Erase any residual.
-    simplifyRegion(region);
+    // Erase any residual (fir.shape, fir.slice...).
+    mlir::IRRewriter rewriter(&context);
+    (void)mlir::runRegionDCE(rewriter, op->getRegions());
   }
 
   void runOnOperation() override final {
@@ -318,48 +320,6 @@ class CodeGenRewrite : public fir::impl::CodeGenRewriteBase<CodeGenRewrite> {
     for (auto global : mod.getOps<fir::GlobalOp>())
       runOn(global, global.getRegion());
   }
-
-  // Clean up the region.
-  void simplifyRegion(mlir::Region &region) {
-    for (auto &block : region.getBlocks())
-      for (auto &op : block.getOperations()) {
-        for (auto &reg : op.getRegions())
-          simplifyRegion(reg);
-        maybeEraseOp(&op);
-      }
-    doDCE();
-  }
-
-  /// Run a simple DCE cleanup to remove any dead code after the rewrites.
-  void doDCE() {
-    std::vector<mlir::Operation *> workList;
-    workList.swap(opsToErase);
-    while (!workList.empty()) {
-      for (auto *op : workList) {
-        std::vector<mlir::Value> opOperands(op->operand_begin(),
-                                            op->operand_end());
-        LLVM_DEBUG(llvm::dbgs() << "DCE on " << *op << '\n');
-        ++numDCE;
-        op->erase();
-        for (auto opnd : opOperands)
-          maybeEraseOp(opnd.getDefiningOp());
-      }
-      workList.clear();
-      workList.swap(opsToErase);
-    }
-  }
-
-  void maybeEraseOp(mlir::Operation *op) {
-    if (!op)
-      return;
-    if (op->hasTrait<mlir::OpTrait::IsTerminator>())
-      return;
-    if (mlir::isOpTriviallyDead(op))
-      opsToErase.push_back(op);
-  }
-
-private:
-  std::vector<mlir::Operation *> opsToErase;
 };
 
 } // namespace
diff --git a/flang/test/Fir/declare-codegen.fir b/flang/test/Fir/declare-codegen.fir
index 1b0bea88e9cff..9d68d3b2f9d4d 100644
--- a/flang/test/Fir/declare-codegen.fir
+++ b/flang/test/Fir/declare-codegen.fir
@@ -18,3 +18,13 @@ func.func private @bar(%arg0: !fir.ref<!fir.array<12x23xi32>>)
 // CHECK-LABEL: func.func @test(
 // CHECK-SAME: %[[arg0:.*]]: !fir.ref<!fir.array<12x23xi32>>) {
 // CHECK-NEXT: fir.call @bar(%[[arg0]]) : (!fir.ref<!fir.array<12x23xi32>>) -> ()
+
+func.func @useless_shape_with_duplicate_extent_operand(%arg0: !fir.ref<!fir.array<3x3xf32>>) {
+  %c3 = arith.constant 3 : index
+  %1 = fir.shape %c3, %c3 : (index, index) -> !fir.shape<2>
+  %2 = fir.declare %arg0(%1) {uniq_name = "u"} : (!fir.ref<!fir.array<3x3xf32>>, !fir.shape<2>) -> !fir.ref<!fir.array<3x3xf32>>
+  return
+}
+
+// CHECK-LABEL: func.func @useless_shape_with_duplicate_extent_operand(
+// CHECK-NEXT: return