1 //===- LoopTransformWarning.cpp -  ----------------------------------------===//
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 // Emit warnings if forced code transformations have not been performed.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "llvm/Transforms/Scalar/WarnMissedTransforms.h"
14 #include "llvm/Analysis/LoopInfo.h"
15 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
16 #include "llvm/Transforms/Utils/LoopUtils.h"
17 
18 using namespace llvm;
19 
20 #define DEBUG_TYPE "transform-warning"
21 
22 /// Emit warnings for forced (i.e. user-defined) loop transformations which have
23 /// still not been performed.
24 static void warnAboutLeftoverTransformations(Loop *L,
25                                              OptimizationRemarkEmitter *ORE) {
26   if (hasUnrollTransformation(L) == TM_ForcedByUser) {
27     LLVM_DEBUG(dbgs() << "Leftover unroll transformation\n");
28     ORE->emit(
29         DiagnosticInfoOptimizationFailure(DEBUG_TYPE,
30                                           "FailedRequestedUnrolling",
31                                           L->getStartLoc(), L->getHeader())
32         << "loop not unrolled: the optimizer was unable to perform the "
33            "requested transformation; the transformation might be disabled or "
34            "specified as part of an unsupported transformation ordering");
35   }
36 
37   if (hasUnrollAndJamTransformation(L) == TM_ForcedByUser) {
38     LLVM_DEBUG(dbgs() << "Leftover unroll-and-jam transformation\n");
39     ORE->emit(
40         DiagnosticInfoOptimizationFailure(DEBUG_TYPE,
41                                           "FailedRequestedUnrollAndJamming",
42                                           L->getStartLoc(), L->getHeader())
43         << "loop not unroll-and-jammed: the optimizer was unable to perform "
44            "the requested transformation; the transformation might be disabled "
45            "or specified as part of an unsupported transformation ordering");
46   }
47 
48   if (hasVectorizeTransformation(L) == TM_ForcedByUser) {
49     LLVM_DEBUG(dbgs() << "Leftover vectorization transformation\n");
50     std::optional<ElementCount> VectorizeWidth =
51         getOptionalElementCountLoopAttribute(L);
52     std::optional<int> InterleaveCount =
53         getOptionalIntLoopAttribute(L, "llvm.loop.interleave.count");
54 
55     if (!VectorizeWidth || VectorizeWidth->isVector())
56       ORE->emit(
57           DiagnosticInfoOptimizationFailure(DEBUG_TYPE,
58                                             "FailedRequestedVectorization",
59                                             L->getStartLoc(), L->getHeader())
60           << "loop not vectorized: the optimizer was unable to perform the "
61              "requested transformation; the transformation might be disabled "
62              "or specified as part of an unsupported transformation ordering");
63     else if (InterleaveCount.value_or(0) != 1)
64       ORE->emit(
65           DiagnosticInfoOptimizationFailure(DEBUG_TYPE,
66                                             "FailedRequestedInterleaving",
67                                             L->getStartLoc(), L->getHeader())
68           << "loop not interleaved: the optimizer was unable to perform the "
69              "requested transformation; the transformation might be disabled "
70              "or specified as part of an unsupported transformation ordering");
71   }
72 
73   if (hasDistributeTransformation(L) == TM_ForcedByUser) {
74     LLVM_DEBUG(dbgs() << "Leftover distribute transformation\n");
75     ORE->emit(
76         DiagnosticInfoOptimizationFailure(DEBUG_TYPE,
77                                           "FailedRequestedDistribution",
78                                           L->getStartLoc(), L->getHeader())
79         << "loop not distributed: the optimizer was unable to perform the "
80            "requested transformation; the transformation might be disabled or "
81            "specified as part of an unsupported transformation ordering");
82   }
83 }
84 
85 static void warnAboutLeftoverTransformations(Function *F, LoopInfo *LI,
86                                              OptimizationRemarkEmitter *ORE) {
87   for (auto *L : LI->getLoopsInPreorder())
88     warnAboutLeftoverTransformations(L, ORE);
89 }
90 
91 // New pass manager boilerplate
92 PreservedAnalyses
93 WarnMissedTransformationsPass::run(Function &F, FunctionAnalysisManager &AM) {
94   // Do not warn about not applied transformations if optimizations are
95   // disabled.
96   if (F.hasOptNone())
97     return PreservedAnalyses::all();
98 
99   auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
100   auto &LI = AM.getResult<LoopAnalysis>(F);
101 
102   warnAboutLeftoverTransformations(&F, &LI, &ORE);
103 
104   return PreservedAnalyses::all();
105 }
106