1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
|
// Copyright (c) 2019 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "source/reduce/merge_blocks_reduction_opportunity.h"
#include "source/opt/block_merge_util.h"
#include "source/opt/ir_context.h"
namespace spvtools {
namespace reduce {
MergeBlocksReductionOpportunity::MergeBlocksReductionOpportunity(
opt::IRContext* context, opt::Function* function, opt::BasicBlock* block) {
// Precondition: the terminator has to be OpBranch.
assert(block->terminator()->opcode() == spv::Op::OpBranch);
context_ = context;
function_ = function;
// Get the successor block associated with the OpBranch.
successor_block_ =
context->cfg()->block(block->terminator()->GetSingleWordInOperand(0));
}
bool MergeBlocksReductionOpportunity::PreconditionHolds() {
// Merge block opportunities can disable each other.
// Example: Given blocks: A->B->C.
// A is a loop header; B and C are blocks in the loop; C ends with OpReturn.
// There are two opportunities: B and C can be merged with their predecessors.
// Merge C. B now ends with OpReturn. We now just have: A->B.
// Merge B is now disabled, as this would lead to A, a loop header, ending
// with an OpReturn, which is invalid.
const auto predecessors = context_->cfg()->preds(successor_block_->id());
assert(1 == predecessors.size() &&
"For a successor to be merged into its predecessor, exactly one "
"predecessor must be present.");
const uint32_t predecessor_id = predecessors[0];
opt::BasicBlock* predecessor_block =
context_->get_instr_block(predecessor_id);
return opt::blockmergeutil::CanMergeWithSuccessor(context_,
predecessor_block);
}
void MergeBlocksReductionOpportunity::Apply() {
// While the original block that targeted the successor may not exist anymore
// (it might have been merged with another block), some block must exist that
// targets the successor. Find it.
const auto predecessors = context_->cfg()->preds(successor_block_->id());
assert(1 == predecessors.size() &&
"For a successor to be merged into its predecessor, exactly one "
"predecessor must be present.");
const uint32_t predecessor_id = predecessors[0];
// We need an iterator pointing to the predecessor, hence the loop.
for (auto bi = function_->begin(); bi != function_->end(); ++bi) {
if (bi->id() == predecessor_id) {
opt::blockmergeutil::MergeWithSuccessor(context_, function_, bi);
// Block merging changes the control flow graph, so invalidate it.
context_->InvalidateAnalysesExceptFor(
opt::IRContext::Analysis::kAnalysisNone);
return;
}
}
assert(false &&
"Unreachable: we should have found a block with the desired id.");
}
} // namespace reduce
} // namespace spvtools
|
