SPIRV-Tools/source/opt/local_single_store_elim_pass.h

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// Copyright (c) 2017 The Khronos Group Inc.
// Copyright (c) 2017 Valve Corporation
// Copyright (c) 2017 LunarG 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_LOCAL_SINGLE_STORE_ELIM_PASS_H_
#define SOURCE_OPT_LOCAL_SINGLE_STORE_ELIM_PASS_H_
#include <algorithm>
#include <map>
#include <queue>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
#include "source/opt/basic_block.h"
#include "source/opt/def_use_manager.h"
#include "source/opt/mem_pass.h"
#include "source/opt/module.h"
namespace spvtools {
namespace opt {
// See optimizer.hpp for documentation.
class LocalSingleStoreElimPass : public Pass {
using cbb_ptr = const BasicBlock*;
public:
LocalSingleStoreElimPass();
const char* name() const override { return "eliminate-local-single-store"; }
Status Process() override;
IRContext::Analysis GetPreservedAnalyses() override {
return IRContext::kAnalysisDefUse |
IRContext::kAnalysisInstrToBlockMapping |
IRContext::kAnalysisConstants | IRContext::kAnalysisTypes;
}
private:
// Do "single-store" optimization of function variables defined only
// with a single non-access-chain store in |func|. Replace all their
// non-access-chain loads with the value that is stored and eliminate
// any resulting dead code.
bool LocalSingleStoreElim(Function* func);
// Initialize extensions allowlist
void InitExtensionAllowList();
// Return true if all extensions in this module are allowed by this pass.
bool AllExtensionsSupported() const;
Pass::Status ProcessImpl();
// If there is a single store to |var_inst|, and it covers the entire
// variable, then replace all of the loads of the entire variable that are
// dominated by the store by the value that was stored. Returns true if the
// module was changed.
bool ProcessVariable(Instruction* var_inst);
// Collects all of the uses of |var_inst| into |uses|. This looks through
// OpObjectCopy's that copy the address of the variable, and collects those
// uses as well.
void FindUses(const Instruction* var_inst,
std::vector<Instruction*>* uses) const;
// Returns a store to |var_inst| if
// - it is a store to the entire variable,
// - and there are no other instructions that may modify |var_inst|.
Instruction* FindSingleStoreAndCheckUses(
Instruction* var_inst, const std::vector<Instruction*>& users) const;
// Returns true if the address that results from |inst| may be used as a base
// address in a store instruction or may be used to compute the base address
// of a store instruction.
bool FeedsAStore(Instruction* inst) const;
// Replaces all of the loads in |uses| by the value stored in |store_inst|.
// The load instructions are then killed. |all_rewritten| is true iff all
// uses have been rewritten.
bool RewriteLoads(Instruction* store_inst,
const std::vector<Instruction*>& uses, bool* all_rewritten);
Add DebugValue for invisible store in single_store_elim (#4002) The front-end language compiler would simply emit DebugDeclare for a variable when it is declared, which is effective through the variable's scope. Since DebugDeclare only maps an OpVariable to a local variable, the information can be removed when an optimization pass uses the loaded value of the variable. DebugValue can be used to specify the value of a variable. For each value update or phi instruction of a variable, we can add DebugValue to help debugger inspect the variable at any point of the program execution. For example, float a = 3; ... (complicated cfg) ... foo(a); // <-- variable inspection: debugger can find DebugValue of `float a` in the nearest dominant For the code with complicated CFG e.g., for-loop, if-statement, we need help of ssa-rewrite to analyze the effective value of each variable in each basic block. If the value update of the variable happens only once and it dominates all its uses, local-single-store-elim pass conducts the same value update with ssa-rewrite and we have to let it add DebugValue for the value assignment. One main issue is that we have to add DebugValue only when the value update of a variable is visible to DebugDeclare. For example, ``` { // scope1 %stack = OpVariable %ptr_int %int_3 { // scope2 DebugDeclare %foo %stack <-- local variable "foo" in high-level language source code is declared as OpVariable "%stack" // add DebugValue "foo = 3" ... Store %stack %int_7 <-- foo = 7, add DebugValue "foo = 7" ... // debugger can inspect the value of "foo" } Store %stack %int_11 <-- out of "scope2" i.e., scope of "foo". DO NOT add DebugValue "foo = 11" } ``` However, the initalization of a variable is an exception. For example, an argument passing of an inlined function must be done out of the function's scope, but we must add a DebugValue for it. ``` // in HLSL bar(float arg) { ... } ... float foo = 3; bar(foo); // in SPIR-V %arg = OpVariable OpStore %arg %foo <-- Argument passing. Out of "float arg" scope, but we must add DebugValue for "float arg" ... body of function bar(float arg) ... ``` This PR handles the except case in local-single-store-elim pass. It adds DebugValue for a store that is considered as an initialization. The same exception handling code for ssa-rewrite is done by this commit: df4198e50eaa705298167d3c0b3cb01ffd28a5ff.
2020-11-04 18:43:59 +00:00
// Replaces DebugDeclares of |var_id| with DebugValues using the value
// assignment of |store_inst|.
bool RewriteDebugDeclares(Instruction* store_inst, uint32_t var_id);
// Extensions supported by this pass.
std::unordered_set<std::string> extensions_allowlist_;
};
} // namespace opt
} // namespace spvtools
#endif // SOURCE_OPT_LOCAL_SINGLE_STORE_ELIM_PASS_H_