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// Copyright (c) 2021 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 <cassert>
#include <sstream>
#include <string>
#include "source/diagnostic.h"
#include "source/lint/divergence_analysis.h"
#include "source/lint/lints.h"
#include "source/opt/basic_block.h"
#include "source/opt/cfg.h"
#include "source/opt/control_dependence.h"
#include "source/opt/def_use_manager.h"
#include "source/opt/dominator_analysis.h"
#include "source/opt/instruction.h"
#include "source/opt/ir_context.h"
#include "spirv-tools/libspirv.h"
namespace spvtools {
namespace lint {
namespace lints {
namespace {
// Returns the %name[id], where `name` is the first name associated with the
// given id, or just %id if one is not found.
std::string GetFriendlyName(opt::IRContext* context, uint32_t id) {
auto names = context->GetNames(id);
std::stringstream ss;
ss << "%";
if (names.empty()) {
ss << id;
} else {
opt::Instruction* inst_name = names.begin()->second;
if (inst_name->opcode() == spv::Op::OpName) {
ss << names.begin()->second->GetInOperand(0).AsString();
ss << "[" << id << "]";
} else {
ss << id;
}
}
return ss.str();
}
bool InstructionHasDerivative(const opt::Instruction& inst) {
static const spv::Op derivative_opcodes[] = {
// Implicit derivatives.
spv::Op::OpImageSampleImplicitLod,
spv::Op::OpImageSampleDrefImplicitLod,
spv::Op::OpImageSampleProjImplicitLod,
spv::Op::OpImageSampleProjDrefImplicitLod,
spv::Op::OpImageSparseSampleImplicitLod,
spv::Op::OpImageSparseSampleDrefImplicitLod,
spv::Op::OpImageSparseSampleProjImplicitLod,
spv::Op::OpImageSparseSampleProjDrefImplicitLod,
// Explicit derivatives.
spv::Op::OpDPdx,
spv::Op::OpDPdy,
spv::Op::OpFwidth,
spv::Op::OpDPdxFine,
spv::Op::OpDPdyFine,
spv::Op::OpFwidthFine,
spv::Op::OpDPdxCoarse,
spv::Op::OpDPdyCoarse,
spv::Op::OpFwidthCoarse,
};
return std::find(std::begin(derivative_opcodes), std::end(derivative_opcodes),
inst.opcode()) != std::end(derivative_opcodes);
}
spvtools::DiagnosticStream Warn(opt::IRContext* context,
opt::Instruction* inst) {
if (inst == nullptr) {
return DiagnosticStream({0, 0, 0}, context->consumer(), "", SPV_WARNING);
} else {
// TODO(kuhar): Use line numbers based on debug info.
return DiagnosticStream(
{0, 0, 0}, context->consumer(),
inst->PrettyPrint(SPV_BINARY_TO_TEXT_OPTION_FRIENDLY_NAMES),
SPV_WARNING);
}
}
void PrintDivergenceFlow(opt::IRContext* context, DivergenceAnalysis div,
uint32_t id) {
opt::analysis::DefUseManager* def_use = context->get_def_use_mgr();
opt::CFG* cfg = context->cfg();
while (id != 0) {
bool is_block = def_use->GetDef(id)->opcode() == spv::Op::OpLabel;
if (is_block) {
Warn(context, nullptr)
<< "block " << GetFriendlyName(context, id) << " is divergent";
uint32_t source = div.GetDivergenceSource(id);
// Skip intermediate blocks.
while (source != 0 &&
def_use->GetDef(source)->opcode() == spv::Op::OpLabel) {
id = source;
source = div.GetDivergenceSource(id);
}
if (source == 0) break;
spvtools::opt::Instruction* branch =
cfg->block(div.GetDivergenceDependenceSource(id))->terminator();
Warn(context, branch)
<< "because it depends on a conditional branch on divergent value "
<< GetFriendlyName(context, source) << "";
id = source;
} else {
Warn(context, nullptr)
<< "value " << GetFriendlyName(context, id) << " is divergent";
uint32_t source = div.GetDivergenceSource(id);
opt::Instruction* def = def_use->GetDef(id);
opt::Instruction* source_def =
source == 0 ? nullptr : def_use->GetDef(source);
// First print data -> data dependencies.
while (source != 0 && source_def->opcode() != spv::Op::OpLabel) {
Warn(context, def_use->GetDef(id))
<< "because " << GetFriendlyName(context, id) << " uses value "
<< GetFriendlyName(context, source)
<< "in its definition, which is divergent";
id = source;
def = source_def;
source = div.GetDivergenceSource(id);
source_def = def_use->GetDef(source);
}
if (source == 0) {
Warn(context, def) << "because it has a divergent definition";
break;
}
Warn(context, def) << "because it is conditionally set in block "
<< GetFriendlyName(context, source);
id = source;
}
}
}
} // namespace
bool CheckDivergentDerivatives(opt::IRContext* context) {
DivergenceAnalysis div(*context);
for (opt::Function& func : *context->module()) {
div.Run(&func);
for (const opt::BasicBlock& bb : func) {
for (const opt::Instruction& inst : bb) {
if (InstructionHasDerivative(inst) &&
div.GetDivergenceLevel(bb.id()) >
DivergenceAnalysis::DivergenceLevel::kPartiallyUniform) {
Warn(context, nullptr)
<< "derivative with divergent control flow"
<< " located in block " << GetFriendlyName(context, bb.id());
PrintDivergenceFlow(context, div, bb.id());
}
}
}
}
return true;
}
} // namespace lints
} // namespace lint
} // namespace spvtools
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