SPIRV-Tools/source/validate_cfg.cpp
Alan Baker c460f44fbc Add a check for invalid exits from case construct.
Fixes #1618.

Adds a check that validates acceptable exits from case constructs. Case
constructs may only exit to another case construct, the corresponding
merge, an outer loop continue or outer loop merge.
2018-07-06 11:52:13 -04:00

638 lines
24 KiB
C++

// 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 "cfa.h"
#include "validate.h"
#include <algorithm>
#include <cassert>
#include <functional>
#include <iostream>
#include <map>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
#include "spirv_validator_options.h"
#include "val/basic_block.h"
#include "val/construct.h"
#include "val/function.h"
#include "val/validation_state.h"
using std::find;
using std::function;
using std::get;
using std::ignore;
using std::make_pair;
using std::make_tuple;
using std::numeric_limits;
using std::pair;
using std::string;
using std::tie;
using std::transform;
using std::tuple;
using std::unordered_map;
using std::unordered_set;
using std::vector;
using libspirv::BasicBlock;
namespace libspirv {
namespace {
using bb_ptr = BasicBlock*;
using cbb_ptr = const BasicBlock*;
using bb_iter = vector<BasicBlock*>::const_iterator;
} // 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())->InstructionPosition())
<< "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())->InstructionPosition())
<< "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 vector<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;
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;
tie(back_edge_block, ignore) = function.GetBlock(back_edge_block_id);
continue_construct->set_exit(back_edge_block);
}
}
}
}
tuple<string, string, string> ConstructNames(ConstructType type) {
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 make_tuple(construct_name, header_name, exit_name);
}
/// Constructs an error message for construct validation errors
string ConstructErrorString(const Construct& construct,
const string& header_string,
const string& exit_string,
const string& dominate_text) {
string construct_name, header_name, exit_name;
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(
const 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)
<< "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) {
*case_fall_through = block->id();
} else if (*case_fall_through != block->id()) {
uint32_t instruction_id =
target_block->label() ? target_block->label()->InstructionPosition()
: -1;
// Case construct has at most one branch to another case construct.
return _.diag(SPV_ERROR_INVALID_CFG, instruction_id)
<< "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(const 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);
std::unordered_set<uint32_t> seen;
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;
if (!seen.insert(target).second) continue;
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)
<< "Selection header " << _.getIdName(header->id())
<< " does not dominate its case construct " << _.getIdName(target);
}
uint32_t case_fall_through = 0u;
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++;
}
}
if (case_fall_through == default_target) {
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->InstructionPosition())
<< "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)->InstructionPosition())
<< "Multiple case constructs have branches to the case construct "
"that targets "
<< _.getIdName(pair.first);
}
}
return SPV_SUCCESS;
}
spv_result_t StructuredControlFlowChecks(
const ValidationState_t& _, Function* function,
const vector<pair<uint32_t, uint32_t>>& back_edges) {
/// 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;
tie(back_edge_block, header_block) = back_edge;
if (!function->IsBlockType(header_block, kBlockTypeLoop)) {
return _.diag(SPV_ERROR_INVALID_CFG)
<< "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)->InstructionPosition())
<< "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) {
string construct_name, header_name, exit_name;
tie(construct_name, header_name, exit_name) =
ConstructNames(construct.type());
return _.diag(SPV_ERROR_INTERNAL,
_.FindDef(header->id())->InstructionPosition())
<< "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())->InstructionPosition())
<< 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())->InstructionPosition())
<< 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())->InstructionPosition())
<< ConstructErrorString(construct, _.getIdName(header->id()),
_.getIdName(merge->id()),
"is not post dominated by");
}
}
// Check that for all non-header blocks, all predecessors are within this
// construct.
Construct::ConstructBlockSet construct_blocks = construct.blocks(function);
for (auto block : construct_blocks) {
if (block == header) continue;
for (auto pred : *block->predecessors()) {
if (pred->reachable() && !construct_blocks.count(pred)) {
string construct_name, header_name, exit_name;
tie(construct_name, header_name, exit_name) =
ConstructNames(construct.type());
return _.diag(SPV_ERROR_INVALID_CFG,
_.FindDef(pred->id())->InstructionPosition())
<< "block <ID> " << pred->id() << " branches to the "
<< construct_name << " construct, but not to the "
<< header_name << " <ID> " << header->id();
}
}
}
// 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;
}
}
}
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) {
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())->InstructionPosition())
<< "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.
vector<const BasicBlock*> postorder;
vector<const BasicBlock*> postdom_postorder;
vector<pair<uint32_t, uint32_t>> back_edges;
auto ignore_block = [](cbb_ptr) {};
auto ignore_edge = [](cbb_ptr, cbb_ptr) {};
if (!function.ordered_blocks().empty()) {
/// calculate dominators
spvtools::CFA<libspirv::BasicBlock>::DepthFirstTraversal(
function.first_block(), function.AugmentedCFGSuccessorsFunction(),
ignore_block, [&](cbb_ptr b) { postorder.push_back(b); },
ignore_edge);
auto edges = spvtools::CFA<libspirv::BasicBlock>::CalculateDominators(
postorder, function.AugmentedCFGPredecessorsFunction());
for (auto edge : edges) {
edge.first->SetImmediateDominator(edge.second);
}
/// calculate post dominators
spvtools::CFA<libspirv::BasicBlock>::DepthFirstTraversal(
function.pseudo_exit_block(),
function.AugmentedCFGPredecessorsFunction(), ignore_block,
[&](cbb_ptr b) { postdom_postorder.push_back(b); }, ignore_edge);
auto postdom_edges =
spvtools::CFA<libspirv::BasicBlock>::CalculateDominators(
postdom_postorder, function.AugmentedCFGSuccessorsFunction());
for (auto edge : postdom_edges) {
edge.first->SetImmediatePostDominator(edge.second);
}
/// calculate back edges.
spvtools::CFA<libspirv::BasicBlock>::DepthFirstTraversal(
function.pseudo_entry_block(),
function
.AugmentedCFGSuccessorsFunctionIncludingHeaderToContinueEdge(),
ignore_block, ignore_block, [&](cbb_ptr from, cbb_ptr 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())->InstructionPosition())
<< "Block " << _.getIdName((*block)->id())
<< " appears in the binary before its dominator "
<< _.getIdName(idom->id());
}
}
}
// 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())->InstructionPosition())
<< "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))
return error;
}
}
return SPV_SUCCESS;
}
spv_result_t CfgPass(ValidationState_t& _, const Instruction* inst) {
SpvOp opcode = static_cast<SpvOp>(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: {
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->InstructionPosition())
<< "OpReturn can only be called from a function with void "
<< "return type.";
}
// Fallthrough.
case SpvOpKill:
case SpvOpReturnValue:
case SpvOpUnreachable:
_.current_function().RegisterBlockEnd(vector<uint32_t>(), opcode);
if (opcode == SpvOpKill) {
_.current_function().RegisterExecutionModelLimitation(
SpvExecutionModelFragment,
"OpKill requires Fragment execution model");
}
break;
default:
break;
}
return SPV_SUCCESS;
}
} // namespace libspirv