1 // Copyright (c) 2019 Google LLC
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // http://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14
15 #include "source/fuzz/fuzzer_pass_adjust_loop_controls.h"
16
17 #include "source/fuzz/transformation_set_loop_control.h"
18
19 namespace spvtools {
20 namespace fuzz {
21
FuzzerPassAdjustLoopControls(opt::IRContext * ir_context,TransformationContext * transformation_context,FuzzerContext * fuzzer_context,protobufs::TransformationSequence * transformations)22 FuzzerPassAdjustLoopControls::FuzzerPassAdjustLoopControls(
23 opt::IRContext* ir_context, TransformationContext* transformation_context,
24 FuzzerContext* fuzzer_context,
25 protobufs::TransformationSequence* transformations)
26 : FuzzerPass(ir_context, transformation_context, fuzzer_context,
27 transformations) {}
28
Apply()29 void FuzzerPassAdjustLoopControls::Apply() {
30 // Consider every merge instruction in the module (via looking through all
31 // functions and blocks).
32 for (auto& function : *GetIRContext()->module()) {
33 for (auto& block : function) {
34 if (auto merge_inst = block.GetMergeInst()) {
35 // Ignore the instruction if it is not a loop merge.
36 if (merge_inst->opcode() != SpvOpLoopMerge) {
37 continue;
38 }
39
40 // Decide randomly whether to adjust this loop merge.
41 if (!GetFuzzerContext()->ChoosePercentage(
42 GetFuzzerContext()->GetChanceOfAdjustingLoopControl())) {
43 continue;
44 }
45
46 uint32_t existing_mask = merge_inst->GetSingleWordOperand(
47 TransformationSetLoopControl::kLoopControlMaskInOperandIndex);
48
49 // First, set the new mask to one of None, Unroll or DontUnroll.
50 std::vector<uint32_t> basic_masks = {SpvLoopControlMaskNone,
51 SpvLoopControlUnrollMask,
52 SpvLoopControlDontUnrollMask};
53 uint32_t new_mask =
54 basic_masks[GetFuzzerContext()->RandomIndex(basic_masks)];
55
56 // For the loop controls that depend on guarantees about what the loop
57 // does, check which of these were present in the existing mask and
58 // randomly decide whether to keep them. They are just hints, so
59 // removing them should not change the semantics of the module.
60 for (auto mask_bit :
61 {SpvLoopControlDependencyInfiniteMask,
62 SpvLoopControlDependencyLengthMask,
63 SpvLoopControlMinIterationsMask, SpvLoopControlMaxIterationsMask,
64 SpvLoopControlIterationMultipleMask}) {
65 if ((existing_mask & mask_bit) && GetFuzzerContext()->ChooseEven()) {
66 // The mask bits we are considering are not available in all SPIR-V
67 // versions. However, we only include a mask bit if it was present
68 // in the original loop control mask, and we work under the
69 // assumption that we are transforming a valid module, thus we don't
70 // need to actually check whether the SPIR-V version being used
71 // supports these loop control mask bits.
72 new_mask |= mask_bit;
73 }
74 }
75
76 // We use 0 for peel count and partial count in the case that we choose
77 // not to set these controls.
78 uint32_t peel_count = 0;
79 uint32_t partial_count = 0;
80
81 // PeelCount and PartialCount are not compatible with DontUnroll, so
82 // we check whether DontUnroll is set.
83 if (!(new_mask & SpvLoopControlDontUnrollMask)) {
84 // If PeelCount is supported by this SPIR-V version, randomly choose
85 // whether to set it. If it was set in the original mask and is not
86 // selected for setting here, that amounts to dropping it.
87 if (TransformationSetLoopControl::PeelCountIsSupported(
88 GetIRContext()) &&
89 GetFuzzerContext()->ChooseEven()) {
90 new_mask |= SpvLoopControlPeelCountMask;
91 // The peel count is chosen randomly - if PeelCount was already set
92 // this will overwrite whatever peel count was previously used.
93 peel_count = GetFuzzerContext()->GetRandomLoopControlPeelCount();
94 }
95 // Similar, but for PartialCount.
96 if (TransformationSetLoopControl::PartialCountIsSupported(
97 GetIRContext()) &&
98 GetFuzzerContext()->ChooseEven()) {
99 new_mask |= SpvLoopControlPartialCountMask;
100 partial_count =
101 GetFuzzerContext()->GetRandomLoopControlPartialCount();
102 }
103 }
104
105 // Apply the transformation and add it to the output transformation
106 // sequence.
107 TransformationSetLoopControl transformation(block.id(), new_mask,
108 peel_count, partial_count);
109 ApplyTransformation(transformation);
110 }
111 }
112 }
113 }
114
115 } // namespace fuzz
116 } // namespace spvtools
117