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SPIRV-Tools/source/opt/fold.cpp
Steven Perron 17cba4695c
Remove undefined behaviour when folding shifts. (#2157) 
We currently simulate all shift operations when the two operand are
constants.  The problem is that if the shift amount is larger than
32, the result is undefined.

I'm changing the folder to return 0 if the shift value is too high.
That way, we will have defined behaviour.

https://crbug.com/910937.
2018-12-04 10:04:02 -05:00

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// Copyright (c) 2017 Google 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 "source/opt/fold.h"
#include <cassert>
#include <cstdint>
#include <vector>
#include "source/opt/const_folding_rules.h"
#include "source/opt/def_use_manager.h"
#include "source/opt/folding_rules.h"
#include "source/opt/ir_builder.h"
#include "source/opt/ir_context.h"
namespace spvtools {
namespace opt {
namespace {
#ifndef INT32_MIN
#define INT32_MIN (-2147483648)
#endif
#ifndef INT32_MAX
#define INT32_MAX 2147483647
#endif
#ifndef UINT32_MAX
#define UINT32_MAX 0xffffffff /* 4294967295U */
#endif
} // namespace
uint32_t InstructionFolder::UnaryOperate(SpvOp opcode, uint32_t operand) const {
switch (opcode) {
// Arthimetics
case SpvOp::SpvOpSNegate:
return -static_cast<int32_t>(operand);
case SpvOp::SpvOpNot:
return ~operand;
case SpvOp::SpvOpLogicalNot:
return !static_cast<bool>(operand);
default:
assert(false &&
"Unsupported unary operation for OpSpecConstantOp instruction");
return 0u;
}
}
uint32_t InstructionFolder::BinaryOperate(SpvOp opcode, uint32_t a,
uint32_t b) const {
switch (opcode) {
// Arthimetics
case SpvOp::SpvOpIAdd:
return a + b;
case SpvOp::SpvOpISub:
return a - b;
case SpvOp::SpvOpIMul:
return a * b;
case SpvOp::SpvOpUDiv:
if (b != 0) {
return a / b;
} else {
// Dividing by 0 is undefined, so we will just pick 0.
return 0;
}
case SpvOp::SpvOpSDiv:
if (b != 0u) {
return (static_cast<int32_t>(a)) / (static_cast<int32_t>(b));
} else {
// Dividing by 0 is undefined, so we will just pick 0.
return 0;
}
case SpvOp::SpvOpSRem: {
// The sign of non-zero result comes from the first operand: a. This is
// guaranteed by C++11 rules for integer division operator. The division
// result is rounded toward zero, so the result of '%' has the sign of
// the first operand.
if (b != 0u) {
return static_cast<int32_t>(a) % static_cast<int32_t>(b);
} else {
// Remainder when dividing with 0 is undefined, so we will just pick 0.
return 0;
}
}
case SpvOp::SpvOpSMod: {
// The sign of non-zero result comes from the second operand: b
if (b != 0u) {
int32_t rem = BinaryOperate(SpvOp::SpvOpSRem, a, b);
int32_t b_prim = static_cast<int32_t>(b);
return (rem + b_prim) % b_prim;
} else {
// Mod with 0 is undefined, so we will just pick 0.
return 0;
}
}
case SpvOp::SpvOpUMod:
if (b != 0u) {
return (a % b);
} else {
// Mod with 0 is undefined, so we will just pick 0.
return 0;
}
// Shifting
case SpvOp::SpvOpShiftRightLogical:
if (b > 32) {
// This is undefined behaviour. Choose 0 for consistency.
return 0;
}
return a >> b;
case SpvOp::SpvOpShiftRightArithmetic:
if (b > 32) {
// This is undefined behaviour. Choose 0 for consistency.
return 0;
}
return (static_cast<int32_t>(a)) >> b;
case SpvOp::SpvOpShiftLeftLogical:
if (b > 32) {
// This is undefined behaviour. Choose 0 for consistency.
return 0;
}
return a << b;
// Bitwise operations
case SpvOp::SpvOpBitwiseOr:
return a | b;
case SpvOp::SpvOpBitwiseAnd:
return a & b;
case SpvOp::SpvOpBitwiseXor:
return a ^ b;
// Logical
case SpvOp::SpvOpLogicalEqual:
return (static_cast<bool>(a)) == (static_cast<bool>(b));
case SpvOp::SpvOpLogicalNotEqual:
return (static_cast<bool>(a)) != (static_cast<bool>(b));
case SpvOp::SpvOpLogicalOr:
return (static_cast<bool>(a)) || (static_cast<bool>(b));
case SpvOp::SpvOpLogicalAnd:
return (static_cast<bool>(a)) && (static_cast<bool>(b));
// Comparison
case SpvOp::SpvOpIEqual:
return a == b;
case SpvOp::SpvOpINotEqual:
return a != b;
case SpvOp::SpvOpULessThan:
return a < b;
case SpvOp::SpvOpSLessThan:
return (static_cast<int32_t>(a)) < (static_cast<int32_t>(b));
case SpvOp::SpvOpUGreaterThan:
return a > b;
case SpvOp::SpvOpSGreaterThan:
return (static_cast<int32_t>(a)) > (static_cast<int32_t>(b));
case SpvOp::SpvOpULessThanEqual:
return a <= b;
case SpvOp::SpvOpSLessThanEqual:
return (static_cast<int32_t>(a)) <= (static_cast<int32_t>(b));
case SpvOp::SpvOpUGreaterThanEqual:
return a >= b;
case SpvOp::SpvOpSGreaterThanEqual:
return (static_cast<int32_t>(a)) >= (static_cast<int32_t>(b));
default:
assert(false &&
"Unsupported binary operation for OpSpecConstantOp instruction");
return 0u;
}
}
uint32_t InstructionFolder::TernaryOperate(SpvOp opcode, uint32_t a, uint32_t b,
uint32_t c) const {
switch (opcode) {
case SpvOp::SpvOpSelect:
return (static_cast<bool>(a)) ? b : c;
default:
assert(false &&
"Unsupported ternary operation for OpSpecConstantOp instruction");
return 0u;
}
}
uint32_t InstructionFolder::OperateWords(
SpvOp opcode, const std::vector<uint32_t>& operand_words) const {
switch (operand_words.size()) {
case 1:
return UnaryOperate(opcode, operand_words.front());
case 2:
return BinaryOperate(opcode, operand_words.front(), operand_words.back());
case 3:
return TernaryOperate(opcode, operand_words[0], operand_words[1],
operand_words[2]);
default:
assert(false && "Invalid number of operands");
return 0;
}
}
bool InstructionFolder::FoldInstructionInternal(Instruction* inst) const {
auto identity_map = [](uint32_t id) { return id; };
Instruction* folded_inst = FoldInstructionToConstant(inst, identity_map);
if (folded_inst != nullptr) {
inst->SetOpcode(SpvOpCopyObject);
inst->SetInOperands({{SPV_OPERAND_TYPE_ID, {folded_inst->result_id()}}});
return true;
}
SpvOp opcode = inst->opcode();
analysis::ConstantManager* const_manager = context_->get_constant_mgr();
std::vector<const analysis::Constant*> constants =
const_manager->GetOperandConstants(inst);
for (const FoldingRule& rule : GetFoldingRules().GetRulesForOpcode(opcode)) {
if (rule(context_, inst, constants)) {
return true;
}
}
return false;
}
// Returns the result of performing an operation on scalar constant operands.
// This function extracts the operand values as 32 bit words and returns the
// result in 32 bit word. Scalar constants with longer than 32-bit width are
// not accepted in this function.
uint32_t InstructionFolder::FoldScalars(
SpvOp opcode,
const std::vector<const analysis::Constant*>& operands) const {
assert(IsFoldableOpcode(opcode) &&
"Unhandled instruction opcode in FoldScalars");
std::vector<uint32_t> operand_values_in_raw_words;
for (const auto& operand : operands) {
if (const analysis::ScalarConstant* scalar = operand->AsScalarConstant()) {
const auto& scalar_words = scalar->words();
assert(scalar_words.size() == 1 &&
"Scalar constants with longer than 32-bit width are not allowed "
"in FoldScalars()");
operand_values_in_raw_words.push_back(scalar_words.front());
} else if (operand->AsNullConstant()) {
operand_values_in_raw_words.push_back(0u);
} else {
assert(false &&
"FoldScalars() only accepts ScalarConst or NullConst type of "
"constant");
}
}
return OperateWords(opcode, operand_values_in_raw_words);
}
bool InstructionFolder::FoldBinaryIntegerOpToConstant(
Instruction* inst, const std::function<uint32_t(uint32_t)>& id_map,
uint32_t* result) const {
SpvOp opcode = inst->opcode();
analysis::ConstantManager* const_manger = context_->get_constant_mgr();
uint32_t ids[2];
const analysis::IntConstant* constants[2];
for (uint32_t i = 0; i < 2; i++) {
const Operand* operand = &inst->GetInOperand(i);
if (operand->type != SPV_OPERAND_TYPE_ID) {
return false;
}
ids[i] = id_map(operand->words[0]);
const analysis::Constant* constant =
const_manger->FindDeclaredConstant(ids[i]);
constants[i] = (constant != nullptr ? constant->AsIntConstant() : nullptr);
}
switch (opcode) {
// Arthimetics
case SpvOp::SpvOpIMul:
for (uint32_t i = 0; i < 2; i++) {
if (constants[i] != nullptr && constants[i]->IsZero()) {
*result = 0;
return true;
}
}
break;
case SpvOp::SpvOpUDiv:
case SpvOp::SpvOpSDiv:
case SpvOp::SpvOpSRem:
case SpvOp::SpvOpSMod:
case SpvOp::SpvOpUMod:
// This changes undefined behaviour (ie divide by 0) into a 0.
for (uint32_t i = 0; i < 2; i++) {
if (constants[i] != nullptr && constants[i]->IsZero()) {
*result = 0;
return true;
}
}
break;
// Shifting
case SpvOp::SpvOpShiftRightLogical:
case SpvOp::SpvOpShiftLeftLogical:
if (constants[1] != nullptr) {
// When shifting by a value larger than the size of the result, the
// result is undefined. We are setting the undefined behaviour to a
// result of 0.
uint32_t shift_amount = constants[1]->GetU32BitValue();
if (shift_amount >= 32) {
*result = 0;
return true;
}
}
break;
// Bitwise operations
case SpvOp::SpvOpBitwiseOr:
for (uint32_t i = 0; i < 2; i++) {
if (constants[i] != nullptr) {
// TODO: Change the mask against a value based on the bit width of the
// instruction result type. This way we can handle say 16-bit values
// as well.
uint32_t mask = constants[i]->GetU32BitValue();
if (mask == 0xFFFFFFFF) {
*result = 0xFFFFFFFF;
return true;
}
}
}
break;
case SpvOp::SpvOpBitwiseAnd:
for (uint32_t i = 0; i < 2; i++) {
if (constants[i] != nullptr) {
if (constants[i]->IsZero()) {
*result = 0;
return true;
}
}
}
break;
// Comparison
case SpvOp::SpvOpULessThan:
if (constants[0] != nullptr &&
constants[0]->GetU32BitValue() == UINT32_MAX) {
*result = false;
return true;
}
if (constants[1] != nullptr && constants[1]->GetU32BitValue() == 0) {
*result = false;
return true;
}
break;
case SpvOp::SpvOpSLessThan:
if (constants[0] != nullptr &&
constants[0]->GetS32BitValue() == INT32_MAX) {
*result = false;
return true;
}
if (constants[1] != nullptr &&
constants[1]->GetS32BitValue() == INT32_MIN) {
*result = false;
return true;
}
break;
case SpvOp::SpvOpUGreaterThan:
if (constants[0] != nullptr && constants[0]->IsZero()) {
*result = false;
return true;
}
if (constants[1] != nullptr &&
constants[1]->GetU32BitValue() == UINT32_MAX) {
*result = false;
return true;
}
break;
case SpvOp::SpvOpSGreaterThan:
if (constants[0] != nullptr &&
constants[0]->GetS32BitValue() == INT32_MIN) {
*result = false;
return true;
}
if (constants[1] != nullptr &&
constants[1]->GetS32BitValue() == INT32_MAX) {
*result = false;
return true;
}
break;
case SpvOp::SpvOpULessThanEqual:
if (constants[0] != nullptr && constants[0]->IsZero()) {
*result = true;
return true;
}
if (constants[1] != nullptr &&
constants[1]->GetU32BitValue() == UINT32_MAX) {
*result = true;
return true;
}
break;
case SpvOp::SpvOpSLessThanEqual:
if (constants[0] != nullptr &&
constants[0]->GetS32BitValue() == INT32_MIN) {
*result = true;
return true;
}
if (constants[1] != nullptr &&
constants[1]->GetS32BitValue() == INT32_MAX) {
*result = true;
return true;
}
break;
case SpvOp::SpvOpUGreaterThanEqual:
if (constants[0] != nullptr &&
constants[0]->GetU32BitValue() == UINT32_MAX) {
*result = true;
return true;
}
if (constants[1] != nullptr && constants[1]->GetU32BitValue() == 0) {
*result = true;
return true;
}
break;
case SpvOp::SpvOpSGreaterThanEqual:
if (constants[0] != nullptr &&
constants[0]->GetS32BitValue() == INT32_MAX) {
*result = true;
return true;
}
if (constants[1] != nullptr &&
constants[1]->GetS32BitValue() == INT32_MIN) {
*result = true;
return true;
}
break;
default:
break;
}
return false;
}
bool InstructionFolder::FoldBinaryBooleanOpToConstant(
Instruction* inst, const std::function<uint32_t(uint32_t)>& id_map,
uint32_t* result) const {
SpvOp opcode = inst->opcode();
analysis::ConstantManager* const_manger = context_->get_constant_mgr();
uint32_t ids[2];
const analysis::BoolConstant* constants[2];
for (uint32_t i = 0; i < 2; i++) {
const Operand* operand = &inst->GetInOperand(i);
if (operand->type != SPV_OPERAND_TYPE_ID) {
return false;
}
ids[i] = id_map(operand->words[0]);
const analysis::Constant* constant =
const_manger->FindDeclaredConstant(ids[i]);
constants[i] = (constant != nullptr ? constant->AsBoolConstant() : nullptr);
}
switch (opcode) {
// Logical
case SpvOp::SpvOpLogicalOr:
for (uint32_t i = 0; i < 2; i++) {
if (constants[i] != nullptr) {
if (constants[i]->value()) {
*result = true;
return true;
}
}
}
break;
case SpvOp::SpvOpLogicalAnd:
for (uint32_t i = 0; i < 2; i++) {
if (constants[i] != nullptr) {
if (!constants[i]->value()) {
*result = false;
return true;
}
}
}
break;
default:
break;
}
return false;
}
bool InstructionFolder::FoldIntegerOpToConstant(
Instruction* inst, const std::function<uint32_t(uint32_t)>& id_map,
uint32_t* result) const {
assert(IsFoldableOpcode(inst->opcode()) &&
"Unhandled instruction opcode in FoldScalars");
switch (inst->NumInOperands()) {
case 2:
return FoldBinaryIntegerOpToConstant(inst, id_map, result) ||
FoldBinaryBooleanOpToConstant(inst, id_map, result);
default:
return false;
}
}
std::vector<uint32_t> InstructionFolder::FoldVectors(
SpvOp opcode, uint32_t num_dims,
const std::vector<const analysis::Constant*>& operands) const {
assert(IsFoldableOpcode(opcode) &&
"Unhandled instruction opcode in FoldVectors");
std::vector<uint32_t> result;
for (uint32_t d = 0; d < num_dims; d++) {
std::vector<uint32_t> operand_values_for_one_dimension;
for (const auto& operand : operands) {
if (const analysis::VectorConstant* vector_operand =
operand->AsVectorConstant()) {
// Extract the raw value of the scalar component constants
// in 32-bit words here. The reason of not using FoldScalars() here
// is that we do not create temporary null constants as components
// when the vector operand is a NullConstant because Constant creation
// may need extra checks for the validity and that is not manageed in
// here.
if (const analysis::ScalarConstant* scalar_component =
vector_operand->GetComponents().at(d)->AsScalarConstant()) {
const auto& scalar_words = scalar_component->words();
assert(
scalar_words.size() == 1 &&
"Vector components with longer than 32-bit width are not allowed "
"in FoldVectors()");
operand_values_for_one_dimension.push_back(scalar_words.front());
} else if (operand->AsNullConstant()) {
operand_values_for_one_dimension.push_back(0u);
} else {
assert(false &&
"VectorConst should only has ScalarConst or NullConst as "
"components");
}
} else if (operand->AsNullConstant()) {
operand_values_for_one_dimension.push_back(0u);
} else {
assert(false &&
"FoldVectors() only accepts VectorConst or NullConst type of "
"constant");
}
}
result.push_back(OperateWords(opcode, operand_values_for_one_dimension));
}
return result;
}
bool InstructionFolder::IsFoldableOpcode(SpvOp opcode) const {
// NOTE: Extend to more opcodes as new cases are handled in the folder
// functions.
switch (opcode) {
case SpvOp::SpvOpBitwiseAnd:
case SpvOp::SpvOpBitwiseOr:
case SpvOp::SpvOpBitwiseXor:
case SpvOp::SpvOpIAdd:
case SpvOp::SpvOpIEqual:
case SpvOp::SpvOpIMul:
case SpvOp::SpvOpINotEqual:
case SpvOp::SpvOpISub:
case SpvOp::SpvOpLogicalAnd:
case SpvOp::SpvOpLogicalEqual:
case SpvOp::SpvOpLogicalNot:
case SpvOp::SpvOpLogicalNotEqual:
case SpvOp::SpvOpLogicalOr:
case SpvOp::SpvOpNot:
case SpvOp::SpvOpSDiv:
case SpvOp::SpvOpSelect:
case SpvOp::SpvOpSGreaterThan:
case SpvOp::SpvOpSGreaterThanEqual:
case SpvOp::SpvOpShiftLeftLogical:
case SpvOp::SpvOpShiftRightArithmetic:
case SpvOp::SpvOpShiftRightLogical:
case SpvOp::SpvOpSLessThan:
case SpvOp::SpvOpSLessThanEqual:
case SpvOp::SpvOpSMod:
case SpvOp::SpvOpSNegate:
case SpvOp::SpvOpSRem:
case SpvOp::SpvOpUDiv:
case SpvOp::SpvOpUGreaterThan:
case SpvOp::SpvOpUGreaterThanEqual:
case SpvOp::SpvOpULessThan:
case SpvOp::SpvOpULessThanEqual:
case SpvOp::SpvOpUMod:
return true;
default:
return false;
}
}
bool InstructionFolder::IsFoldableConstant(
const analysis::Constant* cst) const {
// Currently supported constants are 32-bit values or null constants.
if (const analysis::ScalarConstant* scalar = cst->AsScalarConstant())
return scalar->words().size() == 1;
else
return cst->AsNullConstant() != nullptr;
}
Instruction* InstructionFolder::FoldInstructionToConstant(
Instruction* inst, std::function<uint32_t(uint32_t)> id_map) const {
analysis::ConstantManager* const_mgr = context_->get_constant_mgr();
if (!inst->IsFoldableByFoldScalar() &&
!GetConstantFoldingRules().HasFoldingRule(inst->opcode())) {
return nullptr;
}
// Collect the values of the constant parameters.
std::vector<const analysis::Constant*> constants;
bool missing_constants = false;
inst->ForEachInId([&constants, &missing_constants, const_mgr,
&id_map](uint32_t* op_id) {
uint32_t id = id_map(*op_id);
const analysis::Constant* const_op = const_mgr->FindDeclaredConstant(id);
if (!const_op) {
constants.push_back(nullptr);
missing_constants = true;
} else {
constants.push_back(const_op);
}
});
if (GetConstantFoldingRules().HasFoldingRule(inst->opcode())) {
const analysis::Constant* folded_const = nullptr;
for (auto rule :
GetConstantFoldingRules().GetRulesForOpcode(inst->opcode())) {
folded_const = rule(context_, inst, constants);
if (folded_const != nullptr) {
Instruction* const_inst =
const_mgr->GetDefiningInstruction(folded_const, inst->type_id());
assert(const_inst->type_id() == inst->type_id());
// May be a new instruction that needs to be analysed.
context_->UpdateDefUse(const_inst);
return const_inst;
}
}
}
uint32_t result_val = 0;
bool successful = false;
// If all parameters are constant, fold the instruction to a constant.
if (!missing_constants && inst->IsFoldableByFoldScalar()) {
result_val = FoldScalars(inst->opcode(), constants);
successful = true;
}
if (!successful && inst->IsFoldableByFoldScalar()) {
successful = FoldIntegerOpToConstant(inst, id_map, &result_val);
}
if (successful) {
const analysis::Constant* result_const =
const_mgr->GetConstant(const_mgr->GetType(inst), {result_val});
Instruction* folded_inst =
const_mgr->GetDefiningInstruction(result_const, inst->type_id());
return folded_inst;
}
return nullptr;
}
bool InstructionFolder::IsFoldableType(Instruction* type_inst) const {
// Support 32-bit integers.
if (type_inst->opcode() == SpvOpTypeInt) {
return type_inst->GetSingleWordInOperand(0) == 32;
}
// Support booleans.
if (type_inst->opcode() == SpvOpTypeBool) {
return true;
}
// Nothing else yet.
return false;
}
bool InstructionFolder::FoldInstruction(Instruction* inst) const {
bool modified = false;
Instruction* folded_inst(inst);
while (folded_inst->opcode() != SpvOpCopyObject &&
FoldInstructionInternal(&*folded_inst)) {
modified = true;
}
return modified;
}
} // namespace opt
} // namespace spvtools
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