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https://github.com/KhronosGroup/SPIRV-Tools
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c2b2b57885
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: df4198e50e.
109 lines
3.8 KiB
C++
109 lines
3.8 KiB
C++
// Copyright (c) 2017 The Khronos Group Inc.
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// Copyright (c) 2017 Valve Corporation
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// Copyright (c) 2017 LunarG Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef SOURCE_OPT_LOCAL_SINGLE_STORE_ELIM_PASS_H_
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#define SOURCE_OPT_LOCAL_SINGLE_STORE_ELIM_PASS_H_
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#include <algorithm>
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#include <map>
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#include <queue>
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#include <string>
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#include <unordered_map>
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#include <unordered_set>
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#include <utility>
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#include <vector>
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#include "source/opt/basic_block.h"
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#include "source/opt/def_use_manager.h"
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#include "source/opt/mem_pass.h"
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#include "source/opt/module.h"
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namespace spvtools {
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namespace opt {
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// See optimizer.hpp for documentation.
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class LocalSingleStoreElimPass : public Pass {
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using cbb_ptr = const BasicBlock*;
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public:
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LocalSingleStoreElimPass();
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const char* name() const override { return "eliminate-local-single-store"; }
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Status Process() override;
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IRContext::Analysis GetPreservedAnalyses() override {
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return IRContext::kAnalysisDefUse |
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IRContext::kAnalysisInstrToBlockMapping |
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IRContext::kAnalysisConstants | IRContext::kAnalysisTypes;
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}
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private:
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// Do "single-store" optimization of function variables defined only
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// with a single non-access-chain store in |func|. Replace all their
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// non-access-chain loads with the value that is stored and eliminate
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// any resulting dead code.
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bool LocalSingleStoreElim(Function* func);
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// Initialize extensions allowlist
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void InitExtensionAllowList();
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// Return true if all extensions in this module are allowed by this pass.
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bool AllExtensionsSupported() const;
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Pass::Status ProcessImpl();
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// If there is a single store to |var_inst|, and it covers the entire
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// variable, then replace all of the loads of the entire variable that are
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// dominated by the store by the value that was stored. Returns true if the
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// module was changed.
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bool ProcessVariable(Instruction* var_inst);
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// Collects all of the uses of |var_inst| into |uses|. This looks through
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// OpObjectCopy's that copy the address of the variable, and collects those
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// uses as well.
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void FindUses(const Instruction* var_inst,
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std::vector<Instruction*>* uses) const;
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// Returns a store to |var_inst| if
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// - it is a store to the entire variable,
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// - and there are no other instructions that may modify |var_inst|.
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Instruction* FindSingleStoreAndCheckUses(
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Instruction* var_inst, const std::vector<Instruction*>& users) const;
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// Returns true if the address that results from |inst| may be used as a base
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// address in a store instruction or may be used to compute the base address
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// of a store instruction.
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bool FeedsAStore(Instruction* inst) const;
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// Replaces all of the loads in |uses| by the value stored in |store_inst|.
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// The load instructions are then killed. |all_rewritten| is true iff all
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// uses have been rewritten.
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bool RewriteLoads(Instruction* store_inst,
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const std::vector<Instruction*>& uses, bool* all_rewritten);
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// Replaces DebugDeclares of |var_id| with DebugValues using the value
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// assignment of |store_inst|.
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bool RewriteDebugDeclares(Instruction* store_inst, uint32_t var_id);
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// Extensions supported by this pass.
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std::unordered_set<std::string> extensions_allowlist_;
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};
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} // namespace opt
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} // namespace spvtools
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#endif // SOURCE_OPT_LOCAL_SINGLE_STORE_ELIM_PASS_H_
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