1 //===- TestMemRefDependenceCheck.cpp - Test dep analysis ------------------===//
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 // This file implements a pass to run pair-wise memref access dependence checks.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "mlir/Analysis/AffineAnalysis.h"
14 #include "mlir/Analysis/AffineStructures.h"
15 #include "mlir/Analysis/Utils.h"
16 #include "mlir/Dialect/Affine/IR/AffineOps.h"
17 #include "mlir/IR/Builders.h"
18 #include "mlir/Pass/Pass.h"
19 #include "llvm/Support/Debug.h"
20 
21 #define DEBUG_TYPE "test-memref-dependence-check"
22 
23 using namespace mlir;
24 
25 namespace {
26 
27 // TODO: Add common surrounding loop depth-wise dependence checks.
28 /// Checks dependences between all pairs of memref accesses in a Function.
29 struct TestMemRefDependenceCheck
30     : public PassWrapper<TestMemRefDependenceCheck, FunctionPass> {
31   SmallVector<Operation *, 4> loadsAndStores;
32   void runOnFunction() override;
33 };
34 
35 } // end anonymous namespace
36 
37 // Returns a result string which represents the direction vector (if there was
38 // a dependence), returns the string "false" otherwise.
39 static std::string
40 getDirectionVectorStr(bool ret, unsigned numCommonLoops, unsigned loopNestDepth,
41                       ArrayRef<DependenceComponent> dependenceComponents) {
42   if (!ret)
43     return "false";
44   if (dependenceComponents.empty() || loopNestDepth > numCommonLoops)
45     return "true";
46   std::string result;
47   for (unsigned i = 0, e = dependenceComponents.size(); i < e; ++i) {
48     std::string lbStr = "-inf";
49     if (dependenceComponents[i].lb.hasValue() &&
50         dependenceComponents[i].lb.getValue() !=
51             std::numeric_limits<int64_t>::min())
52       lbStr = std::to_string(dependenceComponents[i].lb.getValue());
53 
54     std::string ubStr = "+inf";
55     if (dependenceComponents[i].ub.hasValue() &&
56         dependenceComponents[i].ub.getValue() !=
57             std::numeric_limits<int64_t>::max())
58       ubStr = std::to_string(dependenceComponents[i].ub.getValue());
59 
60     result += "[" + lbStr + ", " + ubStr + "]";
61   }
62   return result;
63 }
64 
65 // For each access in 'loadsAndStores', runs a dependence check between this
66 // "source" access and all subsequent "destination" accesses in
67 // 'loadsAndStores'. Emits the result of the dependence check as a note with
68 // the source access.
69 static void checkDependences(ArrayRef<Operation *> loadsAndStores) {
70   for (unsigned i = 0, e = loadsAndStores.size(); i < e; ++i) {
71     auto *srcOpInst = loadsAndStores[i];
72     MemRefAccess srcAccess(srcOpInst);
73     for (unsigned j = 0; j < e; ++j) {
74       auto *dstOpInst = loadsAndStores[j];
75       MemRefAccess dstAccess(dstOpInst);
76 
77       unsigned numCommonLoops =
78           getNumCommonSurroundingLoops(*srcOpInst, *dstOpInst);
79       for (unsigned d = 1; d <= numCommonLoops + 1; ++d) {
80         FlatAffineConstraints dependenceConstraints;
81         SmallVector<DependenceComponent, 2> dependenceComponents;
82         DependenceResult result = checkMemrefAccessDependence(
83             srcAccess, dstAccess, d, &dependenceConstraints,
84             &dependenceComponents);
85         assert(result.value != DependenceResult::Failure);
86         bool ret = hasDependence(result);
87         // TODO: Print dependence type (i.e. RAW, etc) and print
88         // distance vectors as: ([2, 3], [0, 10]). Also, shorten distance
89         // vectors from ([1, 1], [3, 3]) to (1, 3).
90         srcOpInst->emitRemark("dependence from ")
91             << i << " to " << j << " at depth " << d << " = "
92             << getDirectionVectorStr(ret, numCommonLoops, d,
93                                      dependenceComponents);
94       }
95     }
96   }
97 }
98 
99 // Walks the Function 'f' adding load and store ops to 'loadsAndStores'.
100 // Runs pair-wise dependence checks.
101 void TestMemRefDependenceCheck::runOnFunction() {
102   // Collect the loads and stores within the function.
103   loadsAndStores.clear();
104   getFunction().walk([&](Operation *op) {
105     if (isa<AffineLoadOp, AffineStoreOp>(op))
106       loadsAndStores.push_back(op);
107   });
108 
109   checkDependences(loadsAndStores);
110 }
111 
112 namespace mlir {
113 namespace test {
114 void registerTestMemRefDependenceCheck() {
115   PassRegistration<TestMemRefDependenceCheck> pass(
116       "test-memref-dependence-check",
117       "Checks dependences between all pairs of memref accesses.");
118 }
119 } // namespace test
120 } // namespace mlir
121