SPIRV-Tools/source/opt/scalar_replacement_pass.h
Steven Perron aef8f92b2b
Even more id overflow in sroa (#2806)
Now we need to handle id overflow when we overflow while replacing uses of the variable.  While looking at this code, I noticed an error in the way we handle access chains that cannot be replaced because of overflow.  Name it will make some change, and then give up by returning SuccessWithoutChange.  But it was changed.

This is fixed up by returning Failure if we notice the error at the time of rewriting the users.  This is for both id overflow or out-of-bounds accesses.

Code is added to "CheckUses" to remove variables that have out-of-bounds accesses from the candidate list, so we don't even try to rewrite its uses.

Fixes https://crbug.com/995032
2019-08-21 13:12:42 -04:00

243 lines
9.6 KiB
C++

// 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.
#ifndef SOURCE_OPT_SCALAR_REPLACEMENT_PASS_H_
#define SOURCE_OPT_SCALAR_REPLACEMENT_PASS_H_
#include <cstdio>
#include <memory>
#include <queue>
#include <unordered_map>
#include <unordered_set>
#include <vector>
#include "source/opt/function.h"
#include "source/opt/pass.h"
#include "source/opt/type_manager.h"
namespace spvtools {
namespace opt {
// Documented in optimizer.hpp
class ScalarReplacementPass : public Pass {
private:
static const uint32_t kDefaultLimit = 100;
public:
ScalarReplacementPass(uint32_t limit = kDefaultLimit)
: max_num_elements_(limit) {
name_[0] = '\0';
strcat(name_, "scalar-replacement=");
sprintf(&name_[strlen(name_)], "%d", max_num_elements_);
}
const char* name() const override { return name_; }
// Attempts to scalarize all appropriate function scope variables. Returns
// SuccessWithChange if any change is made.
Status Process() override;
IRContext::Analysis GetPreservedAnalyses() override {
return IRContext::kAnalysisDefUse |
IRContext::kAnalysisInstrToBlockMapping |
IRContext::kAnalysisDecorations | IRContext::kAnalysisCombinators |
IRContext::kAnalysisCFG | IRContext::kAnalysisNameMap |
IRContext::kAnalysisConstants | IRContext::kAnalysisTypes;
}
private:
// Small container for tracking statistics about variables.
//
// TODO(alanbaker): Develop some useful heuristics to tune this pass.
struct VariableStats {
uint32_t num_partial_accesses;
uint32_t num_full_accesses;
};
// Attempts to scalarize all appropriate function scope variables in
// |function|. Returns SuccessWithChange if any changes are mode.
Status ProcessFunction(Function* function);
// Returns true if |varInst| can be scalarized.
//
// Examines the use chain of |varInst| to verify all uses are valid for
// scalarization.
bool CanReplaceVariable(const Instruction* varInst) const;
// Returns true if |typeInst| is an acceptable type to scalarize.
//
// Allows all aggregate types except runtime arrays. Additionally, checks the
// that the number of elements that would be scalarized is within bounds.
bool CheckType(const Instruction* typeInst) const;
// Returns true if all the decorations for |varInst| are acceptable for
// scalarization.
bool CheckAnnotations(const Instruction* varInst) const;
// Returns true if all the decorations for |typeInst| are acceptable for
// scalarization.
bool CheckTypeAnnotations(const Instruction* typeInst) const;
// Returns true if the uses of |inst| are acceptable for scalarization.
//
// Recursively checks all the uses of |inst|. For |inst| specifically, only
// allows SpvOpAccessChain, SpvOpInBoundsAccessChain, SpvOpLoad and
// SpvOpStore. Access chains must have the first index be a compile-time
// constant. Subsequent uses of access chains (including other access chains)
// are checked in a more relaxed manner.
bool CheckUses(const Instruction* inst) const;
// Helper function for the above |CheckUses|.
//
// This version tracks some stats about the current OpVariable. These stats
// are used to drive heuristics about when to scalarize.
bool CheckUses(const Instruction* inst, VariableStats* stats) const;
// Relaxed helper function for |CheckUses|.
bool CheckUsesRelaxed(const Instruction* inst) const;
// Transfers appropriate decorations from |source| to |replacements|.
void TransferAnnotations(const Instruction* source,
std::vector<Instruction*>* replacements);
// Scalarizes |inst| and updates its uses.
//
// |inst| must be an OpVariable. It is replaced with an OpVariable for each
// for element of the composite type. Uses of |inst| are updated as
// appropriate. If the replacement variables are themselves scalarizable, they
// get added to |worklist| for further processing. If any replacement
// variable ends up with no uses it is erased. Returns
// - Status::SuccessWithoutChange if the variable could not be replaced.
// - Status::SuccessWithChange if it made replacements.
// - Status::Failure if it couldn't create replacement variables.
Pass::Status ReplaceVariable(Instruction* inst,
std::queue<Instruction*>* worklist);
// Returns the underlying storage type for |inst|.
//
// |inst| must be an OpVariable. Returns the type that is pointed to by
// |inst|.
Instruction* GetStorageType(const Instruction* inst) const;
// Returns true if the load can be scalarized.
//
// |inst| must be an OpLoad. Returns true if |index| is the pointer operand of
// |inst| and the load is not from volatile memory.
bool CheckLoad(const Instruction* inst, uint32_t index) const;
// Returns true if the store can be scalarized.
//
// |inst| must be an OpStore. Returns true if |index| is the pointer operand
// of |inst| and the store is not to volatile memory.
bool CheckStore(const Instruction* inst, uint32_t index) const;
// Creates a variable of type |typeId| from the |index|'th element of
// |varInst|. The new variable is added to |replacements|. If the variable
// could not be created, then |nullptr| is appended to |replacements|.
void CreateVariable(uint32_t typeId, Instruction* varInst, uint32_t index,
std::vector<Instruction*>* replacements);
// Populates |replacements| with a new OpVariable for each element of |inst|.
// Returns true if the replacement variables were successfully created.
//
// |inst| must be an OpVariable of a composite type. New variables are
// initialized the same as the corresponding index in |inst|. |replacements|
// will contain a variable for each element of the composite with matching
// indexes (i.e. the 0'th element of |inst| is the 0'th entry of
// |replacements|).
bool CreateReplacementVariables(Instruction* inst,
std::vector<Instruction*>* replacements);
// Returns the array length for |arrayInst|.
uint64_t GetArrayLength(const Instruction* arrayInst) const;
// Returns the number of elements in |type|.
//
// |type| must be a vector or matrix type.
uint64_t GetNumElements(const Instruction* type) const;
// Returns true if |id| is a specialization constant.
//
// |id| must be registered definition.
bool IsSpecConstant(uint32_t id) const;
// Returns an id for a pointer to |id|.
uint32_t GetOrCreatePointerType(uint32_t id);
// Creates the initial value for the |index| element of |source| in |newVar|.
//
// If there is an initial value for |source| for element |index|, it is
// appended as an operand on |newVar|. If the initial value is OpUndef, no
// initial value is added to |newVar|.
void GetOrCreateInitialValue(Instruction* source, uint32_t index,
Instruction* newVar);
// Replaces the load to the entire composite.
//
// Generates a load for each replacement variable and then creates a new
// composite by combining all of the loads.
//
// |load| must be a load. Returns true if successful.
bool ReplaceWholeLoad(Instruction* load,
const std::vector<Instruction*>& replacements);
// Replaces the store to the entire composite.
//
// Generates a composite extract and store for each element in the scalarized
// variable from the original store data input. Returns true if successful.
bool ReplaceWholeStore(Instruction* store,
const std::vector<Instruction*>& replacements);
// Replaces an access chain to the composite variable with either a direct use
// of the appropriate replacement variable or another access chain with the
// replacement variable as the base and one fewer indexes. Returns true if
// successful.
bool ReplaceAccessChain(Instruction* chain,
const std::vector<Instruction*>& replacements);
// Returns a set containing the which components of the result of |inst| are
// potentially used. If the return value is |nullptr|, then every components
// is possibly used.
std::unique_ptr<std::unordered_set<int64_t>> GetUsedComponents(
Instruction* inst);
// Returns an instruction defining a null constant with type |type_id|. If
// one already exists, it is returned. Otherwise a new one is created.
// Returns |nullptr| if the new constant could not be created.
Instruction* CreateNullConstant(uint32_t type_id);
// Maps storage type to a pointer type enclosing that type.
std::unordered_map<uint32_t, uint32_t> pointee_to_pointer_;
// Maps type id to OpConstantNull for that type.
std::unordered_map<uint32_t, uint32_t> type_to_null_;
// Returns the number of elements in the variable |var_inst|.
uint64_t GetMaxLegalIndex(const Instruction* var_inst) const;
// Returns true if |length| is larger than limit on the size of the variable
// that we will be willing to split.
bool IsLargerThanSizeLimit(uint64_t length) const;
// Limit on the number of members in an object that will be replaced.
// 0 means there is no limit.
uint32_t max_num_elements_;
char name_[55];
};
} // namespace opt
} // namespace spvtools
#endif // SOURCE_OPT_SCALAR_REPLACEMENT_PASS_H_