mirror of
https://github.com/KhronosGroup/SPIRV-Tools
synced 2024-10-19 03:20:14 +00:00
4ba9dcc8a0
This implements the conditional constant propagation pass proposed in Constant propagation with conditional branches, Wegman and Zadeck, ACM TOPLAS 13(2):181-210. The main logic resides in CCPPass::VisitInstruction. Instruction that may produce a constant value are evaluated with the constant folder. If they produce a new constant, the instruction is considered interesting. Otherwise, it's considered varying (for unfoldable instructions) or just not interesting (when not enough operands have a constant value). The other main piece of logic is in CCPPass::VisitBranch. This evaluates the selector of the branch. When it's found to be a known value, it computes the destination basic block and sets it. This tells the propagator which branches to follow. The patch required extensions to the constant manager as well. Instead of hashing the Constant pointers, this patch changes the constant pool to hash the contents of the Constant. This allows the lookups to be done using the actual values of the Constant, preventing duplicate definitions.
88 lines
3.3 KiB
C++
88 lines
3.3 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 LIBSPIRV_OPT_CCP_PASS_H_
|
|
#define LIBSPIRV_OPT_CCP_PASS_H_
|
|
|
|
#include "constants.h"
|
|
#include "function.h"
|
|
#include "ir_context.h"
|
|
#include "mem_pass.h"
|
|
#include "module.h"
|
|
#include "propagator.h"
|
|
|
|
namespace spvtools {
|
|
namespace opt {
|
|
|
|
class CCPPass : public MemPass {
|
|
public:
|
|
CCPPass() = default;
|
|
const char* name() const override { return "ccp"; }
|
|
Status Process(ir::IRContext* c) override;
|
|
|
|
private:
|
|
// Initializes the pass.
|
|
void Initialize(ir::IRContext* c);
|
|
|
|
// Runs constant propagation on the given function |fp|. Returns true if any
|
|
// constants were propagated and the IR modified.
|
|
bool PropagateConstants(ir::Function* fp);
|
|
|
|
// Visits a single instruction |instr|. If the instruction is a conditional
|
|
// branch that always jumps to the same basic block, it sets the destination
|
|
// block in |dest_bb|.
|
|
SSAPropagator::PropStatus VisitInstruction(ir::Instruction* instr,
|
|
ir::BasicBlock** dest_bb);
|
|
|
|
// Visits an OpPhi instruction |phi|. This applies the meet operator for the
|
|
// CCP lattice. Essentially, if all the operands in |phi| have the same
|
|
// constant value C, the result for |phi| gets assigned the value C.
|
|
SSAPropagator::PropStatus VisitPhi(ir::Instruction* phi);
|
|
|
|
// Visits an SSA assignment instruction |instr|. If the RHS of |instr| folds
|
|
// into a constant value C, then the LHS of |instr| is assigned the value C in
|
|
// |values_|.
|
|
SSAPropagator::PropStatus VisitAssignment(ir::Instruction* instr);
|
|
|
|
// Visits a branch instruction |instr|. If the branch is conditional
|
|
// (OpBranchConditional or OpSwitch), and the value of its selector is known,
|
|
// |dest_bb| will be set to the corresponding destination block. Unconditional
|
|
// branches always set |dest_bb| to the single destination block.
|
|
SSAPropagator::PropStatus VisitBranch(ir::Instruction* instr,
|
|
ir::BasicBlock** dest_bb) const;
|
|
|
|
// Replaces all operands used in |fp| with the corresponding constant values
|
|
// in |values_|. Returns true if any operands were replaced, and false
|
|
// otherwise.
|
|
bool ReplaceValues();
|
|
|
|
// Constant manager for the parent IR context. Used to record new constants
|
|
// generated during propagation.
|
|
analysis::ConstantManager* const_mgr_;
|
|
|
|
// Constant value table. Each entry <id, const_decl_id> in this map
|
|
// represents the compile-time constant value for |id| as declared by
|
|
// |const_decl_id|. Each |const_decl_id| in this table is an OpConstant
|
|
// declaration for the current module.
|
|
std::unordered_map<uint32_t, uint32_t> values_;
|
|
|
|
// Propagator engine used.
|
|
std::unique_ptr<SSAPropagator> propagator_;
|
|
};
|
|
|
|
} // namespace opt
|
|
} // namespace spvtools
|
|
|
|
#endif
|