1 //===- TestConstantFold.cpp - Pass to test constant folding ---------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #include "mlir/Pass/Pass.h"
10 #include "mlir/Transforms/FoldUtils.h"
11 #include "mlir/Transforms/Passes.h"
12 #include "mlir/Transforms/Utils.h"
13 
14 using namespace mlir;
15 
16 namespace {
17 /// Simple constant folding pass.
18 struct TestConstantFold : public PassWrapper<TestConstantFold, FunctionPass> {
19   StringRef getArgument() const final { return "test-constant-fold"; }
20   StringRef getDescription() const final {
21     return "Test operation constant folding";
22   }
23   // All constants in the function post folding.
24   SmallVector<Operation *, 8> existingConstants;
25 
26   void foldOperation(Operation *op, OperationFolder &helper);
27   void runOnFunction() override;
28 };
29 } // end anonymous namespace
30 
31 void TestConstantFold::foldOperation(Operation *op, OperationFolder &helper) {
32   auto processGeneratedConstants = [this](Operation *op) {
33     existingConstants.push_back(op);
34   };
35 
36   // Attempt to fold the specified operation, including handling unused or
37   // duplicated constants.
38   (void)helper.tryToFold(op, processGeneratedConstants);
39 }
40 
41 // For now, we do a simple top-down pass over a function folding constants.  We
42 // don't handle conditional control flow, block arguments, folding conditional
43 // branches, or anything else fancy.
44 void TestConstantFold::runOnFunction() {
45   existingConstants.clear();
46 
47   // Collect and fold the operations within the function.
48   SmallVector<Operation *, 8> ops;
49   getFunction().walk([&](Operation *op) { ops.push_back(op); });
50 
51   // Fold the constants in reverse so that the last generated constants from
52   // folding are at the beginning. This creates somewhat of a linear ordering to
53   // the newly generated constants that matches the operation order and improves
54   // the readability of test cases.
55   OperationFolder helper(&getContext());
56   for (Operation *op : llvm::reverse(ops))
57     foldOperation(op, helper);
58 
59   // By the time we are done, we may have simplified a bunch of code, leaving
60   // around dead constants.  Check for them now and remove them.
61   for (auto *cst : existingConstants) {
62     if (cst->use_empty())
63       cst->erase();
64   }
65 }
66 
67 namespace mlir {
68 namespace test {
69 void registerTestConstantFold() { PassRegistration<TestConstantFold>(); }
70 } // namespace test
71 } // namespace mlir
72