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SPIRV-Tools/source/val/validate_cfg.cpp
alan-baker 2a2bdbd5d7
Remove implicit fallthrough (#3298) 
Fixes #3296

* Make OpReturn its own case fully
2020-04-14 12:57:48 -04:00

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// Copyright (c) 2015-2016 The Khronos Group 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 <algorithm>
#include <cassert>
#include <functional>
#include <iostream>
#include <iterator>
#include <map>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
#include "source/cfa.h"
#include "source/opcode.h"
#include "source/spirv_target_env.h"
#include "source/spirv_validator_options.h"
#include "source/val/basic_block.h"
#include "source/val/construct.h"
#include "source/val/function.h"
#include "source/val/validate.h"
#include "source/val/validation_state.h"
namespace spvtools {
namespace val {
namespace {
spv_result_t ValidatePhi(ValidationState_t& _, const Instruction* inst) {
auto block = inst->block();
size_t num_in_ops = inst->words().size() - 3;
if (num_in_ops % 2 != 0) {
return _.diag(SPV_ERROR_INVALID_ID, inst)
<< "OpPhi does not have an equal number of incoming values and "
"basic blocks.";
}
const Instruction* type_inst = _.FindDef(inst->type_id());
assert(type_inst);
const SpvOp type_opcode = type_inst->opcode();
if (type_opcode == SpvOpTypePointer &&
_.addressing_model() == SpvAddressingModelLogical) {
if (!_.features().variable_pointers &&
!_.features().variable_pointers_storage_buffer) {
return _.diag(SPV_ERROR_INVALID_DATA, inst)
<< "Using pointers with OpPhi requires capability "
<< "VariablePointers or VariablePointersStorageBuffer";
}
}
if (!_.options()->before_hlsl_legalization) {
if (type_opcode == SpvOpTypeSampledImage ||
(_.HasCapability(SpvCapabilityShader) &&
(type_opcode == SpvOpTypeImage || type_opcode == SpvOpTypeSampler))) {
return _.diag(SPV_ERROR_INVALID_ID, inst)
<< "Result type cannot be Op" << spvOpcodeString(type_opcode);
}
}
// Create a uniqued vector of predecessor ids for comparison against
// incoming values. OpBranchConditional %cond %label %label produces two
// predecessors in the CFG.
std::vector<uint32_t> pred_ids;
std::transform(block->predecessors()->begin(), block->predecessors()->end(),
std::back_inserter(pred_ids),
[](const BasicBlock* b) { return b->id(); });
std::sort(pred_ids.begin(), pred_ids.end());
pred_ids.erase(std::unique(pred_ids.begin(), pred_ids.end()), pred_ids.end());
size_t num_edges = num_in_ops / 2;
if (num_edges != pred_ids.size()) {
return _.diag(SPV_ERROR_INVALID_ID, inst)
<< "OpPhi's number of incoming blocks (" << num_edges
<< ") does not match block's predecessor count ("
<< block->predecessors()->size() << ").";
}
for (size_t i = 3; i < inst->words().size(); ++i) {
auto inc_id = inst->word(i);
if (i % 2 == 1) {
// Incoming value type must match the phi result type.
auto inc_type_id = _.GetTypeId(inc_id);
if (inst->type_id() != inc_type_id) {
return _.diag(SPV_ERROR_INVALID_ID, inst)
<< "OpPhi's result type <id> " << _.getIdName(inst->type_id())
<< " does not match incoming value <id> " << _.getIdName(inc_id)
<< " type <id> " << _.getIdName(inc_type_id) << ".";
}
} else {
if (_.GetIdOpcode(inc_id) != SpvOpLabel) {
return _.diag(SPV_ERROR_INVALID_ID, inst)
<< "OpPhi's incoming basic block <id> " << _.getIdName(inc_id)
<< " is not an OpLabel.";
}
// Incoming basic block must be an immediate predecessor of the phi's
// block.
if (!std::binary_search(pred_ids.begin(), pred_ids.end(), inc_id)) {
return _.diag(SPV_ERROR_INVALID_ID, inst)
<< "OpPhi's incoming basic block <id> " << _.getIdName(inc_id)
<< " is not a predecessor of <id> " << _.getIdName(block->id())
<< ".";
}
}
}
return SPV_SUCCESS;
}
spv_result_t ValidateBranch(ValidationState_t& _, const Instruction* inst) {
// target operands must be OpLabel
const auto id = inst->GetOperandAs<uint32_t>(0);
const auto target = _.FindDef(id);
if (!target || SpvOpLabel != target->opcode()) {
return _.diag(SPV_ERROR_INVALID_ID, inst)
<< "'Target Label' operands for OpBranch must be the ID "
"of an OpLabel instruction";
}
return SPV_SUCCESS;
}
spv_result_t ValidateBranchConditional(ValidationState_t& _,
const Instruction* inst) {
// num_operands is either 3 or 5 --- if 5, the last two need to be literal
// integers
const auto num_operands = inst->operands().size();
if (num_operands != 3 && num_operands != 5) {
return _.diag(SPV_ERROR_INVALID_ID, inst)
<< "OpBranchConditional requires either 3 or 5 parameters";
}
// grab the condition operand and check that it is a bool
const auto cond_id = inst->GetOperandAs<uint32_t>(0);
const auto cond_op = _.FindDef(cond_id);
if (!cond_op || !cond_op->type_id() ||
!_.IsBoolScalarType(cond_op->type_id())) {
return _.diag(SPV_ERROR_INVALID_ID, inst) << "Condition operand for "
"OpBranchConditional must be "
"of boolean type";
}
// target operands must be OpLabel
// note that we don't need to check that the target labels are in the same
// function,
// PerformCfgChecks already checks for that
const auto true_id = inst->GetOperandAs<uint32_t>(1);
const auto true_target = _.FindDef(true_id);
if (!true_target || SpvOpLabel != true_target->opcode()) {
return _.diag(SPV_ERROR_INVALID_ID, inst)
<< "The 'True Label' operand for OpBranchConditional must be the "
"ID of an OpLabel instruction";
}
const auto false_id = inst->GetOperandAs<uint32_t>(2);
const auto false_target = _.FindDef(false_id);
if (!false_target || SpvOpLabel != false_target->opcode()) {
return _.diag(SPV_ERROR_INVALID_ID, inst)
<< "The 'False Label' operand for OpBranchConditional must be the "
"ID of an OpLabel instruction";
}
return SPV_SUCCESS;
}
spv_result_t ValidateSwitch(ValidationState_t& _, const Instruction* inst) {
const auto num_operands = inst->operands().size();
// At least two operands (selector, default), any more than that are
// literal/target.
// target operands must be OpLabel
for (size_t i = 2; i < num_operands; i += 2) {
// literal, id
const auto id = inst->GetOperandAs<uint32_t>(i + 1);
const auto target = _.FindDef(id);
if (!target || SpvOpLabel != target->opcode()) {
return _.diag(SPV_ERROR_INVALID_ID, inst)
<< "'Target Label' operands for OpSwitch must be IDs of an "
"OpLabel instruction";
}
}
return SPV_SUCCESS;
}
spv_result_t ValidateReturnValue(ValidationState_t& _,
const Instruction* inst) {
const auto value_id = inst->GetOperandAs<uint32_t>(0);
const auto value = _.FindDef(value_id);
if (!value || !value->type_id()) {
return _.diag(SPV_ERROR_INVALID_ID, inst)
<< "OpReturnValue Value <id> '" << _.getIdName(value_id)
<< "' does not represent a value.";
}
auto value_type = _.FindDef(value->type_id());
if (!value_type || SpvOpTypeVoid == value_type->opcode()) {
return _.diag(SPV_ERROR_INVALID_ID, inst)
<< "OpReturnValue value's type <id> '"
<< _.getIdName(value->type_id()) << "' is missing or void.";
}
const bool uses_variable_pointer =
_.features().variable_pointers ||
_.features().variable_pointers_storage_buffer;
if (_.addressing_model() == SpvAddressingModelLogical &&
SpvOpTypePointer == value_type->opcode() && !uses_variable_pointer &&
!_.options()->relax_logical_pointer) {
return _.diag(SPV_ERROR_INVALID_ID, inst)
<< "OpReturnValue value's type <id> '"
<< _.getIdName(value->type_id())
<< "' is a pointer, which is invalid in the Logical addressing "
"model.";
}
const auto function = inst->function();
const auto return_type = _.FindDef(function->GetResultTypeId());
if (!return_type || return_type->id() != value_type->id()) {
return _.diag(SPV_ERROR_INVALID_ID, inst)
<< "OpReturnValue Value <id> '" << _.getIdName(value_id)
<< "'s type does not match OpFunction's return type.";
}
return SPV_SUCCESS;
}
spv_result_t ValidateLoopMerge(ValidationState_t& _, const Instruction* inst) {
const auto merge_id = inst->GetOperandAs<uint32_t>(0);
const auto merge = _.FindDef(merge_id);
if (!merge || merge->opcode() != SpvOpLabel) {
return _.diag(SPV_ERROR_INVALID_ID, inst)
<< "Merge Block " << _.getIdName(merge_id) << " must be an OpLabel";
}
if (merge_id == inst->block()->id()) {
return _.diag(SPV_ERROR_INVALID_ID, inst)
<< "Merge Block may not be the block containing the OpLoopMerge\n";
}
const auto continue_id = inst->GetOperandAs<uint32_t>(1);
const auto continue_target = _.FindDef(continue_id);
if (!continue_target || continue_target->opcode() != SpvOpLabel) {
return _.diag(SPV_ERROR_INVALID_ID, inst)
<< "Continue Target " << _.getIdName(continue_id)
<< " must be an OpLabel";
}
if (merge_id == continue_id) {
return _.diag(SPV_ERROR_INVALID_ID, inst)
<< "Merge Block and Continue Target must be different ids";
}
const auto loop_control = inst->GetOperandAs<uint32_t>(2);
if ((loop_control >> SpvLoopControlUnrollShift) & 0x1 &&
(loop_control >> SpvLoopControlDontUnrollShift) & 0x1) {
return _.diag(SPV_ERROR_INVALID_DATA, inst)
<< "Unroll and DontUnroll loop controls must not both be specified";
}
if ((loop_control >> SpvLoopControlDontUnrollShift) & 0x1 &&
(loop_control >> SpvLoopControlPeelCountShift) & 0x1) {
return _.diag(SPV_ERROR_INVALID_DATA, inst) << "PeelCount and DontUnroll "
"loop controls must not "
"both be specified";
}
if ((loop_control >> SpvLoopControlDontUnrollShift) & 0x1 &&
(loop_control >> SpvLoopControlPartialCountShift) & 0x1) {
return _.diag(SPV_ERROR_INVALID_DATA, inst) << "PartialCount and "
"DontUnroll loop controls "
"must not both be specified";
}
uint32_t operand = 3;
if ((loop_control >> SpvLoopControlDependencyLengthShift) & 0x1) {
++operand;
}
if ((loop_control >> SpvLoopControlMinIterationsShift) & 0x1) {
++operand;
}
if ((loop_control >> SpvLoopControlMaxIterationsShift) & 0x1) {
++operand;
}
if ((loop_control >> SpvLoopControlIterationMultipleShift) & 0x1) {
if (inst->operands().size() < operand ||
inst->GetOperandAs<uint32_t>(operand) == 0) {
return _.diag(SPV_ERROR_INVALID_DATA, inst) << "IterationMultiple loop "
"control operand must be "
"greater than zero";
}
++operand;
}
if ((loop_control >> SpvLoopControlPeelCountShift) & 0x1) {
++operand;
}
if ((loop_control >> SpvLoopControlPartialCountShift) & 0x1) {
++operand;
}
// That the right number of operands is present is checked by the parser. The
// above code tracks operands for expanded validation checking in the future.
return SPV_SUCCESS;
}
} // namespace
void printDominatorList(const BasicBlock& b) {
std::cout << b.id() << " is dominated by: ";
const BasicBlock* bb = &b;
while (bb->immediate_dominator() != bb) {
bb = bb->immediate_dominator();
std::cout << bb->id() << " ";
}
}
#define CFG_ASSERT(ASSERT_FUNC, TARGET) \
if (spv_result_t rcode = ASSERT_FUNC(_, TARGET)) return rcode
spv_result_t FirstBlockAssert(ValidationState_t& _, uint32_t target) {
if (_.current_function().IsFirstBlock(target)) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(_.current_function().id()))
<< "First block " << _.getIdName(target) << " of function "
<< _.getIdName(_.current_function().id()) << " is targeted by block "
<< _.getIdName(_.current_function().current_block()->id());
}
return SPV_SUCCESS;
}
spv_result_t MergeBlockAssert(ValidationState_t& _, uint32_t merge_block) {
if (_.current_function().IsBlockType(merge_block, kBlockTypeMerge)) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(_.current_function().id()))
<< "Block " << _.getIdName(merge_block)
<< " is already a merge block for another header";
}
return SPV_SUCCESS;
}
/// Update the continue construct's exit blocks once the backedge blocks are
/// identified in the CFG.
void UpdateContinueConstructExitBlocks(
Function& function,
const std::vector<std::pair<uint32_t, uint32_t>>& back_edges) {
auto& constructs = function.constructs();
// TODO(umar): Think of a faster way to do this
for (auto& edge : back_edges) {
uint32_t back_edge_block_id;
uint32_t loop_header_block_id;
std::tie(back_edge_block_id, loop_header_block_id) = edge;
auto is_this_header = [=](Construct& c) {
return c.type() == ConstructType::kLoop &&
c.entry_block()->id() == loop_header_block_id;
};
for (auto construct : constructs) {
if (is_this_header(construct)) {
Construct* continue_construct =
construct.corresponding_constructs().back();
assert(continue_construct->type() == ConstructType::kContinue);
BasicBlock* back_edge_block;
std::tie(back_edge_block, std::ignore) =
function.GetBlock(back_edge_block_id);
continue_construct->set_exit(back_edge_block);
}
}
}
}
std::tuple<std::string, std::string, std::string> ConstructNames(
ConstructType type) {
std::string construct_name, header_name, exit_name;
switch (type) {
case ConstructType::kSelection:
construct_name = "selection";
header_name = "selection header";
exit_name = "merge block";
break;
case ConstructType::kLoop:
construct_name = "loop";
header_name = "loop header";
exit_name = "merge block";
break;
case ConstructType::kContinue:
construct_name = "continue";
header_name = "continue target";
exit_name = "back-edge block";
break;
case ConstructType::kCase:
construct_name = "case";
header_name = "case entry block";
exit_name = "case exit block";
break;
default:
assert(1 == 0 && "Not defined type");
}
return std::make_tuple(construct_name, header_name, exit_name);
}
/// Constructs an error message for construct validation errors
std::string ConstructErrorString(const Construct& construct,
const std::string& header_string,
const std::string& exit_string,
const std::string& dominate_text) {
std::string construct_name, header_name, exit_name;
std::tie(construct_name, header_name, exit_name) =
ConstructNames(construct.type());
// TODO(umar): Add header block for continue constructs to error message
return "The " + construct_name + " construct with the " + header_name + " " +
header_string + " " + dominate_text + " the " + exit_name + " " +
exit_string;
}
// Finds the fall through case construct of |target_block| and records it in
// |case_fall_through|. Returns SPV_ERROR_INVALID_CFG if the case construct
// headed by |target_block| branches to multiple case constructs.
spv_result_t FindCaseFallThrough(
ValidationState_t& _, BasicBlock* target_block, uint32_t* case_fall_through,
const BasicBlock* merge, const std::unordered_set<uint32_t>& case_targets,
Function* function) {
std::vector<BasicBlock*> stack;
stack.push_back(target_block);
std::unordered_set<const BasicBlock*> visited;
bool target_reachable = target_block->reachable();
int target_depth = function->GetBlockDepth(target_block);
while (!stack.empty()) {
auto block = stack.back();
stack.pop_back();
if (block == merge) continue;
if (!visited.insert(block).second) continue;
if (target_reachable && block->reachable() &&
target_block->dominates(*block)) {
// Still in the case construct.
for (auto successor : *block->successors()) {
stack.push_back(successor);
}
} else {
// Exiting the case construct to non-merge block.
if (!case_targets.count(block->id())) {
int depth = function->GetBlockDepth(block);
if ((depth < target_depth) ||
(depth == target_depth && block->is_type(kBlockTypeContinue))) {
continue;
}
return _.diag(SPV_ERROR_INVALID_CFG, target_block->label())
<< "Case construct that targets "
<< _.getIdName(target_block->id())
<< " has invalid branch to block " << _.getIdName(block->id())
<< " (not another case construct, corresponding merge, outer "
"loop merge or outer loop continue)";
}
if (*case_fall_through == 0u) {
if (target_block != block) {
*case_fall_through = block->id();
}
} else if (*case_fall_through != block->id()) {
// Case construct has at most one branch to another case construct.
return _.diag(SPV_ERROR_INVALID_CFG, target_block->label())
<< "Case construct that targets "
<< _.getIdName(target_block->id())
<< " has branches to multiple other case construct targets "
<< _.getIdName(*case_fall_through) << " and "
<< _.getIdName(block->id());
}
}
}
return SPV_SUCCESS;
}
spv_result_t StructuredSwitchChecks(ValidationState_t& _, Function* function,
const Instruction* switch_inst,
const BasicBlock* header,
const BasicBlock* merge) {
std::unordered_set<uint32_t> case_targets;
for (uint32_t i = 1; i < switch_inst->operands().size(); i += 2) {
uint32_t target = switch_inst->GetOperandAs<uint32_t>(i);
if (target != merge->id()) case_targets.insert(target);
}
// Tracks how many times each case construct is targeted by another case
// construct.
std::map<uint32_t, uint32_t> num_fall_through_targeted;
uint32_t default_case_fall_through = 0u;
uint32_t default_target = switch_inst->GetOperandAs<uint32_t>(1u);
bool default_appears_multiple_times = false;
for (uint32_t i = 3; i < switch_inst->operands().size(); i += 2) {
if (default_target == switch_inst->GetOperandAs<uint32_t>(i)) {
default_appears_multiple_times = true;
break;
}
}
std::unordered_map<uint32_t, uint32_t> seen_to_fall_through;
for (uint32_t i = 1; i < switch_inst->operands().size(); i += 2) {
uint32_t target = switch_inst->GetOperandAs<uint32_t>(i);
if (target == merge->id()) continue;
uint32_t case_fall_through = 0u;
auto seen_iter = seen_to_fall_through.find(target);
if (seen_iter == seen_to_fall_through.end()) {
const auto target_block = function->GetBlock(target).first;
// OpSwitch must dominate all its case constructs.
if (header->reachable() && target_block->reachable() &&
!header->dominates(*target_block)) {
return _.diag(SPV_ERROR_INVALID_CFG, header->label())
<< "Selection header " << _.getIdName(header->id())
<< " does not dominate its case construct "
<< _.getIdName(target);
}
if (auto error = FindCaseFallThrough(_, target_block, &case_fall_through,
merge, case_targets, function)) {
return error;
}
// Track how many time the fall through case has been targeted.
if (case_fall_through != 0u) {
auto where = num_fall_through_targeted.lower_bound(case_fall_through);
if (where == num_fall_through_targeted.end() ||
where->first != case_fall_through) {
num_fall_through_targeted.insert(
where, std::make_pair(case_fall_through, 1));
} else {
where->second++;
}
}
seen_to_fall_through.insert(std::make_pair(target, case_fall_through));
} else {
case_fall_through = seen_iter->second;
}
if (case_fall_through == default_target &&
!default_appears_multiple_times) {
case_fall_through = default_case_fall_through;
}
if (case_fall_through != 0u) {
bool is_default = i == 1;
if (is_default) {
default_case_fall_through = case_fall_through;
} else {
// Allow code like:
// case x:
// case y:
// ...
// case z:
//
// Where x and y target the same block and fall through to z.
uint32_t j = i;
while ((j + 2 < switch_inst->operands().size()) &&
target == switch_inst->GetOperandAs<uint32_t>(j + 2)) {
j += 2;
}
// If Target T1 branches to Target T2, or if Target T1 branches to the
// Default target and the Default target branches to Target T2, then T1
// must immediately precede T2 in the list of OpSwitch Target operands.
if ((switch_inst->operands().size() < j + 2) ||
(case_fall_through != switch_inst->GetOperandAs<uint32_t>(j + 2))) {
return _.diag(SPV_ERROR_INVALID_CFG, switch_inst)
<< "Case construct that targets " << _.getIdName(target)
<< " has branches to the case construct that targets "
<< _.getIdName(case_fall_through)
<< ", but does not immediately precede it in the "
"OpSwitch's target list";
}
}
}
}
// Each case construct must be branched to by at most one other case
// construct.
for (const auto& pair : num_fall_through_targeted) {
if (pair.second > 1) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(pair.first))
<< "Multiple case constructs have branches to the case construct "
"that targets "
<< _.getIdName(pair.first);
}
}
return SPV_SUCCESS;
}
// Validates that all CFG divergences (i.e. conditional branch or switch) are
// structured correctly. Either divergence is preceded by a merge instruction
// or the divergence introduces at most one unseen label.
spv_result_t ValidateStructuredSelections(
ValidationState_t& _, const std::vector<const BasicBlock*>& postorder) {
std::unordered_set<uint32_t> seen;
for (auto iter = postorder.rbegin(); iter != postorder.rend(); ++iter) {
const auto* block = *iter;
const auto* terminator = block->terminator();
if (!terminator) continue;
const auto index = terminator - &_.ordered_instructions()[0];
auto* merge = &_.ordered_instructions()[index - 1];
// Marks merges and continues as seen.
if (merge->opcode() == SpvOpSelectionMerge) {
seen.insert(merge->GetOperandAs<uint32_t>(0));
} else if (merge->opcode() == SpvOpLoopMerge) {
seen.insert(merge->GetOperandAs<uint32_t>(0));
seen.insert(merge->GetOperandAs<uint32_t>(1));
} else {
// Only track the pointer if it is a merge instruction.
merge = nullptr;
}
// Skip unreachable blocks.
if (!block->reachable()) continue;
if (terminator->opcode() == SpvOpBranchConditional) {
const auto true_label = terminator->GetOperandAs<uint32_t>(1);
const auto false_label = terminator->GetOperandAs<uint32_t>(2);
// Mark the upcoming blocks as seen now, but only error out if this block
// was missing a merge instruction and both labels hadn't been seen
// previously.
const bool both_unseen =
seen.insert(true_label).second && seen.insert(false_label).second;
if (!merge && both_unseen) {
return _.diag(SPV_ERROR_INVALID_CFG, terminator)
<< "Selection must be structured";
}
} else if (terminator->opcode() == SpvOpSwitch) {
uint32_t count = 0;
// Mark the targets as seen now, but only error out if this block was
// missing a merge instruction and there were multiple unseen labels.
for (uint32_t i = 1; i < terminator->operands().size(); i += 2) {
const auto target = terminator->GetOperandAs<uint32_t>(i);
if (seen.insert(target).second) {
count++;
}
}
if (!merge && count > 1) {
return _.diag(SPV_ERROR_INVALID_CFG, terminator)
<< "Selection must be structured";
}
}
}
return SPV_SUCCESS;
}
spv_result_t StructuredControlFlowChecks(
ValidationState_t& _, Function* function,
const std::vector<std::pair<uint32_t, uint32_t>>& back_edges,
const std::vector<const BasicBlock*>& postorder) {
/// Check all backedges target only loop headers and have exactly one
/// back-edge branching to it
// Map a loop header to blocks with back-edges to the loop header.
std::map<uint32_t, std::unordered_set<uint32_t>> loop_latch_blocks;
for (auto back_edge : back_edges) {
uint32_t back_edge_block;
uint32_t header_block;
std::tie(back_edge_block, header_block) = back_edge;
if (!function->IsBlockType(header_block, kBlockTypeLoop)) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(back_edge_block))
<< "Back-edges (" << _.getIdName(back_edge_block) << " -> "
<< _.getIdName(header_block)
<< ") can only be formed between a block and a loop header.";
}
loop_latch_blocks[header_block].insert(back_edge_block);
}
// Check the loop headers have exactly one back-edge branching to it
for (BasicBlock* loop_header : function->ordered_blocks()) {
if (!loop_header->reachable()) continue;
if (!loop_header->is_type(kBlockTypeLoop)) continue;
auto loop_header_id = loop_header->id();
auto num_latch_blocks = loop_latch_blocks[loop_header_id].size();
if (num_latch_blocks != 1) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(loop_header_id))
<< "Loop header " << _.getIdName(loop_header_id)
<< " is targeted by " << num_latch_blocks
<< " back-edge blocks but the standard requires exactly one";
}
}
// Check construct rules
for (const Construct& construct : function->constructs()) {
auto header = construct.entry_block();
auto merge = construct.exit_block();
if (header->reachable() && !merge) {
std::string construct_name, header_name, exit_name;
std::tie(construct_name, header_name, exit_name) =
ConstructNames(construct.type());
return _.diag(SPV_ERROR_INTERNAL, _.FindDef(header->id()))
<< "Construct " + construct_name + " with " + header_name + " " +
_.getIdName(header->id()) + " does not have a " +
exit_name + ". This may be a bug in the validator.";
}
// If the exit block is reachable then it's dominated by the
// header.
if (merge && merge->reachable()) {
if (!header->dominates(*merge)) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(merge->id()))
<< ConstructErrorString(construct, _.getIdName(header->id()),
_.getIdName(merge->id()),
"does not dominate");
}
// If it's really a merge block for a selection or loop, then it must be
// *strictly* dominated by the header.
if (construct.ExitBlockIsMergeBlock() && (header == merge)) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(merge->id()))
<< ConstructErrorString(construct, _.getIdName(header->id()),
_.getIdName(merge->id()),
"does not strictly dominate");
}
}
// Check post-dominance for continue constructs. But dominance and
// post-dominance only make sense when the construct is reachable.
if (header->reachable() && construct.type() == ConstructType::kContinue) {
if (!merge->postdominates(*header)) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(merge->id()))
<< ConstructErrorString(construct, _.getIdName(header->id()),
_.getIdName(merge->id()),
"is not post dominated by");
}
}
Construct::ConstructBlockSet construct_blocks = construct.blocks(function);
std::string construct_name, header_name, exit_name;
std::tie(construct_name, header_name, exit_name) =
ConstructNames(construct.type());
for (auto block : construct_blocks) {
// Check that all exits from the construct are via structured exits.
for (auto succ : *block->successors()) {
if (block->reachable() && !construct_blocks.count(succ) &&
!construct.IsStructuredExit(_, succ)) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(block->id()))
<< "block <ID> " << _.getIdName(block->id()) << " exits the "
<< construct_name << " headed by <ID> "
<< _.getIdName(header->id())
<< ", but not via a structured exit";
}
}
if (block == header) continue;
// Check that for all non-header blocks, all predecessors are within this
// construct.
for (auto pred : *block->predecessors()) {
if (pred->reachable() && !construct_blocks.count(pred)) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(pred->id()))
<< "block <ID> " << pred->id() << " branches to the "
<< construct_name << " construct, but not to the "
<< header_name << " <ID> " << header->id();
}
}
if (block->is_type(BlockType::kBlockTypeSelection) ||
block->is_type(BlockType::kBlockTypeLoop)) {
size_t index = (block->terminator() - &_.ordered_instructions()[0]) - 1;
const auto& merge_inst = _.ordered_instructions()[index];
if (merge_inst.opcode() == SpvOpSelectionMerge ||
merge_inst.opcode() == SpvOpLoopMerge) {
uint32_t merge_id = merge_inst.GetOperandAs<uint32_t>(0);
auto merge_block = function->GetBlock(merge_id).first;
if (merge_block->reachable() &&
!construct_blocks.count(merge_block)) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(block->id()))
<< "Header block " << _.getIdName(block->id())
<< " is contained in the " << construct_name
<< " construct headed by " << _.getIdName(header->id())
<< ", but its merge block " << _.getIdName(merge_id)
<< " is not";
}
}
}
}
// Checks rules for case constructs.
if (construct.type() == ConstructType::kSelection &&
header->terminator()->opcode() == SpvOpSwitch) {
const auto terminator = header->terminator();
if (auto error =
StructuredSwitchChecks(_, function, terminator, header, merge)) {
return error;
}
}
}
if (auto error = ValidateStructuredSelections(_, postorder)) {
return error;
}
return SPV_SUCCESS;
}
spv_result_t PerformWebGPUCfgChecks(ValidationState_t& _, Function* function) {
for (auto& block : function->ordered_blocks()) {
if (block->reachable()) continue;
if (block->is_type(kBlockTypeMerge)) {
// 1. Find the referencing merge and confirm that it is reachable.
BasicBlock* merge_header = function->GetMergeHeader(block);
assert(merge_header != nullptr);
if (!merge_header->reachable()) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(block->id()))
<< "For WebGPU, unreachable merge-blocks must be referenced by "
"a reachable merge instruction.";
}
// 2. Check that the only instructions are OpLabel and OpUnreachable.
auto* label_inst = block->label();
auto* terminator_inst = block->terminator();
assert(label_inst != nullptr);
assert(terminator_inst != nullptr);
if (terminator_inst->opcode() != SpvOpUnreachable) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(block->id()))
<< "For WebGPU, unreachable merge-blocks must terminate with "
"OpUnreachable.";
}
auto label_idx = label_inst - &_.ordered_instructions()[0];
auto terminator_idx = terminator_inst - &_.ordered_instructions()[0];
if (label_idx + 1 != terminator_idx) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(block->id()))
<< "For WebGPU, unreachable merge-blocks must only contain an "
"OpLabel and OpUnreachable instruction.";
}
// 3. Use label instruction to confirm there is no uses by branches.
for (auto use : label_inst->uses()) {
const auto* use_inst = use.first;
if (spvOpcodeIsBranch(use_inst->opcode())) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(block->id()))
<< "For WebGPU, unreachable merge-blocks cannot be the target "
"of a branch.";
}
}
} else if (block->is_type(kBlockTypeContinue)) {
// 1. Find referencing loop and confirm that it is reachable.
std::vector<BasicBlock*> continue_headers =
function->GetContinueHeaders(block);
if (continue_headers.empty()) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(block->id()))
<< "For WebGPU, unreachable continue-target must be referenced "
"by a loop instruction.";
}
std::vector<BasicBlock*> reachable_headers(continue_headers.size());
auto iter =
std::copy_if(continue_headers.begin(), continue_headers.end(),
reachable_headers.begin(),
[](BasicBlock* header) { return header->reachable(); });
reachable_headers.resize(std::distance(reachable_headers.begin(), iter));
if (reachable_headers.empty()) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(block->id()))
<< "For WebGPU, unreachable continue-target must be referenced "
"by a reachable loop instruction.";
}
// 2. Check that the only instructions are OpLabel and OpBranch.
auto* label_inst = block->label();
auto* terminator_inst = block->terminator();
assert(label_inst != nullptr);
assert(terminator_inst != nullptr);
if (terminator_inst->opcode() != SpvOpBranch) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(block->id()))
<< "For WebGPU, unreachable continue-target must terminate with "
"OpBranch.";
}
auto label_idx = label_inst - &_.ordered_instructions()[0];
auto terminator_idx = terminator_inst - &_.ordered_instructions()[0];
if (label_idx + 1 != terminator_idx) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(block->id()))
<< "For WebGPU, unreachable continue-target must only contain "
"an OpLabel and an OpBranch instruction.";
}
// 3. Use label instruction to confirm there is no uses by branches.
for (auto use : label_inst->uses()) {
const auto* use_inst = use.first;
if (spvOpcodeIsBranch(use_inst->opcode())) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(block->id()))
<< "For WebGPU, unreachable continue-target cannot be the "
"target of a branch.";
}
}
// 4. Confirm that continue-target has a back edge to a reachable loop
// header block.
auto branch_target = terminator_inst->GetOperandAs<uint32_t>(0);
for (auto* continue_header : reachable_headers) {
if (branch_target != continue_header->id()) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(block->id()))
<< "For WebGPU, unreachable continue-target must only have a "
"back edge to a single reachable loop instruction.";
}
}
} else {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(block->id()))
<< "For WebGPU, all blocks must be reachable, unless they are "
<< "degenerate cases of merge-block or continue-target.";
}
}
return SPV_SUCCESS;
}
spv_result_t PerformCfgChecks(ValidationState_t& _) {
for (auto& function : _.functions()) {
// Check all referenced blocks are defined within a function
if (function.undefined_block_count() != 0) {
std::string undef_blocks("{");
bool first = true;
for (auto undefined_block : function.undefined_blocks()) {
undef_blocks += _.getIdName(undefined_block);
if (!first) {
undef_blocks += " ";
}
first = false;
}
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(function.id()))
<< "Block(s) " << undef_blocks << "}"
<< " are referenced but not defined in function "
<< _.getIdName(function.id());
}
// Set each block's immediate dominator and immediate postdominator,
// and find all back-edges.
//
// We want to analyze all the blocks in the function, even in degenerate
// control flow cases including unreachable blocks. So use the augmented
// CFG to ensure we cover all the blocks.
std::vector<const BasicBlock*> postorder;
std::vector<const BasicBlock*> postdom_postorder;
std::vector<std::pair<uint32_t, uint32_t>> back_edges;
auto ignore_block = [](const BasicBlock*) {};
auto ignore_edge = [](const BasicBlock*, const BasicBlock*) {};
if (!function.ordered_blocks().empty()) {
/// calculate dominators
CFA<BasicBlock>::DepthFirstTraversal(
function.first_block(), function.AugmentedCFGSuccessorsFunction(),
ignore_block, [&](const BasicBlock* b) { postorder.push_back(b); },
ignore_edge);
auto edges = CFA<BasicBlock>::CalculateDominators(
postorder, function.AugmentedCFGPredecessorsFunction());
for (auto edge : edges) {
if (edge.first != edge.second)
edge.first->SetImmediateDominator(edge.second);
}
/// calculate post dominators
CFA<BasicBlock>::DepthFirstTraversal(
function.pseudo_exit_block(),
function.AugmentedCFGPredecessorsFunction(), ignore_block,
[&](const BasicBlock* b) { postdom_postorder.push_back(b); },
ignore_edge);
auto postdom_edges = CFA<BasicBlock>::CalculateDominators(
postdom_postorder, function.AugmentedCFGSuccessorsFunction());
for (auto edge : postdom_edges) {
edge.first->SetImmediatePostDominator(edge.second);
}
/// calculate back edges.
CFA<BasicBlock>::DepthFirstTraversal(
function.pseudo_entry_block(),
function
.AugmentedCFGSuccessorsFunctionIncludingHeaderToContinueEdge(),
ignore_block, ignore_block,
[&](const BasicBlock* from, const BasicBlock* to) {
back_edges.emplace_back(from->id(), to->id());
});
}
UpdateContinueConstructExitBlocks(function, back_edges);
auto& blocks = function.ordered_blocks();
if (!blocks.empty()) {
// Check if the order of blocks in the binary appear before the blocks
// they dominate
for (auto block = begin(blocks) + 1; block != end(blocks); ++block) {
if (auto idom = (*block)->immediate_dominator()) {
if (idom != function.pseudo_entry_block() &&
block == std::find(begin(blocks), block, idom)) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(idom->id()))
<< "Block " << _.getIdName((*block)->id())
<< " appears in the binary before its dominator "
<< _.getIdName(idom->id());
}
}
// For WebGPU check that all unreachable blocks are degenerate cases for
// merge-block or continue-target.
if (spvIsWebGPUEnv(_.context()->target_env)) {
spv_result_t result = PerformWebGPUCfgChecks(_, &function);
if (result != SPV_SUCCESS) return result;
}
}
// If we have structed control flow, check that no block has a control
// flow nesting depth larger than the limit.
if (_.HasCapability(SpvCapabilityShader)) {
const int control_flow_nesting_depth_limit =
_.options()->universal_limits_.max_control_flow_nesting_depth;
for (auto block = begin(blocks); block != end(blocks); ++block) {
if (function.GetBlockDepth(*block) >
control_flow_nesting_depth_limit) {
return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef((*block)->id()))
<< "Maximum Control Flow nesting depth exceeded.";
}
}
}
}
/// Structured control flow checks are only required for shader capabilities
if (_.HasCapability(SpvCapabilityShader)) {
if (auto error =
StructuredControlFlowChecks(_, &function, back_edges, postorder))
return error;
}
}
return SPV_SUCCESS;
}
spv_result_t CfgPass(ValidationState_t& _, const Instruction* inst) {
SpvOp opcode = inst->opcode();
switch (opcode) {
case SpvOpLabel:
if (auto error = _.current_function().RegisterBlock(inst->id()))
return error;
// TODO(github:1661) This should be done in the
// ValidationState::RegisterInstruction method but because of the order of
// passes the OpLabel ends up not being part of the basic block it starts.
_.current_function().current_block()->set_label(inst);
break;
case SpvOpLoopMerge: {
uint32_t merge_block = inst->GetOperandAs<uint32_t>(0);
uint32_t continue_block = inst->GetOperandAs<uint32_t>(1);
CFG_ASSERT(MergeBlockAssert, merge_block);
if (auto error = _.current_function().RegisterLoopMerge(merge_block,
continue_block))
return error;
} break;
case SpvOpSelectionMerge: {
uint32_t merge_block = inst->GetOperandAs<uint32_t>(0);
CFG_ASSERT(MergeBlockAssert, merge_block);
if (auto error = _.current_function().RegisterSelectionMerge(merge_block))
return error;
} break;
case SpvOpBranch: {
uint32_t target = inst->GetOperandAs<uint32_t>(0);
CFG_ASSERT(FirstBlockAssert, target);
_.current_function().RegisterBlockEnd({target}, opcode);
} break;
case SpvOpBranchConditional: {
uint32_t tlabel = inst->GetOperandAs<uint32_t>(1);
uint32_t flabel = inst->GetOperandAs<uint32_t>(2);
CFG_ASSERT(FirstBlockAssert, tlabel);
CFG_ASSERT(FirstBlockAssert, flabel);
_.current_function().RegisterBlockEnd({tlabel, flabel}, opcode);
} break;
case SpvOpSwitch: {
std::vector<uint32_t> cases;
for (size_t i = 1; i < inst->operands().size(); i += 2) {
uint32_t target = inst->GetOperandAs<uint32_t>(i);
CFG_ASSERT(FirstBlockAssert, target);
cases.push_back(target);
}
_.current_function().RegisterBlockEnd({cases}, opcode);
} break;
case SpvOpReturn: {
const uint32_t return_type = _.current_function().GetResultTypeId();
const Instruction* return_type_inst = _.FindDef(return_type);
assert(return_type_inst);
if (return_type_inst->opcode() != SpvOpTypeVoid)
return _.diag(SPV_ERROR_INVALID_CFG, inst)
<< "OpReturn can only be called from a function with void "
<< "return type.";
_.current_function().RegisterBlockEnd(std::vector<uint32_t>(), opcode);
break;
}
case SpvOpKill:
case SpvOpReturnValue:
case SpvOpUnreachable:
_.current_function().RegisterBlockEnd(std::vector<uint32_t>(), opcode);
if (opcode == SpvOpKill) {
_.current_function().RegisterExecutionModelLimitation(
SpvExecutionModelFragment,
"OpKill requires Fragment execution model");
}
break;
default:
break;
}
return SPV_SUCCESS;
}
spv_result_t ControlFlowPass(ValidationState_t& _, const Instruction* inst) {
switch (inst->opcode()) {
case SpvOpPhi:
if (auto error = ValidatePhi(_, inst)) return error;
break;
case SpvOpBranch:
if (auto error = ValidateBranch(_, inst)) return error;
break;
case SpvOpBranchConditional:
if (auto error = ValidateBranchConditional(_, inst)) return error;
break;
case SpvOpReturnValue:
if (auto error = ValidateReturnValue(_, inst)) return error;
break;
case SpvOpSwitch:
if (auto error = ValidateSwitch(_, inst)) return error;
break;
case SpvOpLoopMerge:
if (auto error = ValidateLoopMerge(_, inst)) return error;
break;
default:
break;
}
return SPV_SUCCESS;
}
} // namespace val
} // namespace spvtools
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