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// Copyright (c) 2017 The Khronos Group Inc.
// Copyright (c) 2017 Valve Corporation
// Copyright (c) 2017 LunarG Inc.
//
// 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 "block_merge_pass.h"
#include "iterator.h"
namespace spvtools {
namespace opt {
namespace {
const int kEntryPointFunctionIdInIdx = 1;
} // anonymous namespace
bool BlockMergePass::IsLoopHeader(ir::BasicBlock* block_ptr) {
auto iItr = block_ptr->tail();
if (iItr == block_ptr->begin())
return false;
--iItr;
return iItr->opcode() == SpvOpLoopMerge;
}
bool BlockMergePass::HasMultipleRefs(uint32_t labId) {
const analysis::UseList* uses = def_use_mgr_->GetUses(labId);
int rcnt = 0;
for (const auto u : *uses) {
// Don't count OpName
if (u.inst->opcode() == SpvOpName)
continue;
if (rcnt == 1)
return true;
++rcnt;
}
return false;
}
void BlockMergePass::KillInstAndName(ir::Instruction* inst) {
const uint32_t id = inst->result_id();
if (id != 0) {
analysis::UseList* uses = def_use_mgr_->GetUses(id);
if (uses != nullptr)
for (auto u : *uses)
if (u.inst->opcode() == SpvOpName) {
def_use_mgr_->KillInst(u.inst);
break;
}
}
def_use_mgr_->KillInst(inst);
}
bool BlockMergePass::MergeBlocks(ir::Function* func) {
bool modified = false;
for (auto bi = func->begin(); bi != func->end(); ) {
// Do not merge loop header blocks, at least for now.
if (IsLoopHeader(&*bi)) {
++bi;
continue;
}
// Find block with single successor which has no other predecessors.
// Continue and Merge blocks are currently ruled out as second blocks.
// Happily any such candidate blocks will have >1 uses due to their
// LoopMerge instruction.
// TODO(): Deal with phi instructions that reference the
// second block. Happily, these references currently inhibit
// the merge.
auto ii = bi->end();
--ii;
ir::Instruction* br = &*ii;
if (br->opcode() != SpvOpBranch) {
++bi;
continue;
}
const uint32_t labId = br->GetSingleWordInOperand(0);
if (HasMultipleRefs(labId)) {
++bi;
continue;
}
// Merge blocks
def_use_mgr_->KillInst(br);
auto sbi = bi;
for (; sbi != func->end(); ++sbi)
if (sbi->id() == labId)
break;
// If bi is sbi's only predecessor, it dominates sbi and thus
// sbi must follow bi in func's ordering.
assert(sbi != func->end());
bi->AddInstructions(&*sbi);
KillInstAndName(sbi->GetLabelInst());
(void) sbi.Erase();
// reprocess block
modified = true;
}
return modified;
}
void BlockMergePass::Initialize(ir::Module* module) {
module_ = module;
// Initialize function and block maps
id2function_.clear();
for (auto& fn : *module_)
id2function_[fn.result_id()] = &fn;
// TODO(greg-lunarg): Reuse def/use from previous passes
def_use_mgr_.reset(new analysis::DefUseManager(consumer(), module_));
// Initialize extension whitelist
InitExtensions();
};
bool BlockMergePass::AllExtensionsSupported() const {
// If any extension not in whitelist, return false
for (auto& ei : module_->extensions()) {
const char* extName = reinterpret_cast<const char*>(
&ei.GetInOperand(0).words[0]);
if (extensions_whitelist_.find(extName) == extensions_whitelist_.end())
return false;
}
return true;
}
Pass::Status BlockMergePass::ProcessImpl() {
// Do not process if any disallowed extensions are enabled
if (!AllExtensionsSupported())
return Status::SuccessWithoutChange;
bool modified = false;
for (auto& e : module_->entry_points()) {
ir::Function* fn =
id2function_[e.GetSingleWordInOperand(kEntryPointFunctionIdInIdx)];
modified = MergeBlocks(fn) || modified;
}
return modified ? Status::SuccessWithChange : Status::SuccessWithoutChange;
}
BlockMergePass::BlockMergePass()
: module_(nullptr), def_use_mgr_(nullptr) {}
Pass::Status BlockMergePass::Process(ir::Module* module) {
Initialize(module);
return ProcessImpl();
}
void BlockMergePass::InitExtensions() {
extensions_whitelist_.clear();
extensions_whitelist_.insert({
"SPV_AMD_shader_explicit_vertex_parameter",
"SPV_AMD_shader_trinary_minmax",
"SPV_AMD_gcn_shader",
"SPV_KHR_shader_ballot",
"SPV_AMD_shader_ballot",
"SPV_AMD_gpu_shader_half_float",
"SPV_KHR_shader_draw_parameters",
"SPV_KHR_subgroup_vote",
"SPV_KHR_16bit_storage",
"SPV_KHR_device_group",
"SPV_KHR_multiview",
"SPV_NVX_multiview_per_view_attributes",
"SPV_NV_viewport_array2",
"SPV_NV_stereo_view_rendering",
"SPV_NV_sample_mask_override_coverage",
"SPV_NV_geometry_shader_passthrough",
"SPV_AMD_texture_gather_bias_lod",
"SPV_KHR_storage_buffer_storage_class",
"SPV_KHR_variable_pointers",
"SPV_AMD_gpu_shader_int16",
"SPV_KHR_post_depth_coverage",
"SPV_KHR_shader_atomic_counter_ops",
});
}
} // namespace opt
} // namespace spvtools
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