SPIRV-Tools/source/opt/block_merge_pass.cpp
Steven Perron 2d2a512691
Don't inline recursive functions. (#2130)
* Move ProcessFunction* function from pass to the context.

There are a few functions that are used to traverse the call tree.
They currently live in the Pass class, but they have nothing to do with
a pass, and may be needed outside of a pass.  They would be better in
the ir context, or in a specific call tree class if we ever have a need
for it.

* Don't inline recursive functions.

Inlining does not check if a function is recursive or not.  This has
been fine as long as the shader was a Vulkan shader, which forbid
recursive functions.  However, not all shaders are vulkan, so either
we limit inlining to Vulkan shaders or we teach it to look for recursive
functions.

I prefer to keep the passes as general as is reasonable.  The change
does not require much new code in inlining and gives a reason to refactor
some other code.

The changes are to add a member function to the Function class that
checks if that function is recursive or not.

Then this is used in inlining to not inlining a function call if it calls
a recursive function.

* Add id to function analysis

There are a few places that build a map from ids to Function whose
result is that id.  I decided to add an analysis to the context for this
to reduce that code, and simplify some of the functions.

* Add missing file.
2018-11-29 14:24:58 -05:00

147 lines
4.7 KiB
C++

// 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.
#include "source/opt/block_merge_pass.h"
#include <vector>
#include "source/opt/ir_context.h"
#include "source/opt/iterator.h"
namespace spvtools {
namespace opt {
bool BlockMergePass::MergeBlocks(Function* func) {
bool modified = false;
for (auto bi = func->begin(); bi != func->end();) {
// Find block with single successor which has no other predecessors.
auto ii = bi->end();
--ii;
Instruction* br = &*ii;
if (br->opcode() != SpvOpBranch) {
++bi;
continue;
}
const uint32_t lab_id = br->GetSingleWordInOperand(0);
if (cfg()->preds(lab_id).size() != 1) {
++bi;
continue;
}
bool pred_is_merge = IsMerge(&*bi);
bool succ_is_merge = IsMerge(lab_id);
if (pred_is_merge && succ_is_merge) {
// Cannot merge two merges together.
++bi;
continue;
}
Instruction* merge_inst = bi->GetMergeInst();
bool pred_is_header = IsHeader(&*bi);
if (pred_is_header && lab_id != merge_inst->GetSingleWordInOperand(0u)) {
bool succ_is_header = IsHeader(lab_id);
if (pred_is_header && succ_is_header) {
// Cannot merge two headers together when the successor is not the merge
// block of the predecessor.
++bi;
continue;
}
// If this is a header block and the successor is not its merge, we must
// be careful about which blocks we are willing to merge together.
// OpLoopMerge must be followed by a conditional or unconditional branch.
// The merge must be a loop merge because a selection merge cannot be
// followed by an unconditional branch.
BasicBlock* succ_block = context()->get_instr_block(lab_id);
SpvOp succ_term_op = succ_block->terminator()->opcode();
assert(merge_inst->opcode() == SpvOpLoopMerge);
if (succ_term_op != SpvOpBranch &&
succ_term_op != SpvOpBranchConditional) {
++bi;
continue;
}
}
// Merge blocks.
context()->KillInst(br);
auto sbi = bi;
for (; sbi != func->end(); ++sbi)
if (sbi->id() == lab_id) break;
// If bi is sbi's only predecessor, it dominates sbi and thus
// sbi must follow bi in func's ordering.
assert(sbi != func->end());
// Update the inst-to-block mapping for the instructions in sbi.
for (auto& inst : *sbi) {
context()->set_instr_block(&inst, &*bi);
}
// Now actually move the instructions.
bi->AddInstructions(&*sbi);
if (merge_inst) {
if (pred_is_header && lab_id == merge_inst->GetSingleWordInOperand(0u)) {
// Merging the header and merge blocks, so remove the structured control
// flow declaration.
context()->KillInst(merge_inst);
} else {
// Move the merge instruction to just before the terminator.
merge_inst->InsertBefore(bi->terminator());
}
}
context()->ReplaceAllUsesWith(lab_id, bi->id());
context()->KillInst(sbi->GetLabelInst());
(void)sbi.Erase();
// Reprocess block.
modified = true;
}
return modified;
}
bool BlockMergePass::IsHeader(BasicBlock* block) {
return block->GetMergeInst() != nullptr;
}
bool BlockMergePass::IsHeader(uint32_t id) {
return IsHeader(context()->get_instr_block(get_def_use_mgr()->GetDef(id)));
}
bool BlockMergePass::IsMerge(uint32_t id) {
return !get_def_use_mgr()->WhileEachUse(id, [](Instruction* user,
uint32_t index) {
SpvOp op = user->opcode();
if ((op == SpvOpLoopMerge || op == SpvOpSelectionMerge) && index == 0u) {
return false;
}
return true;
});
}
bool BlockMergePass::IsMerge(BasicBlock* block) { return IsMerge(block->id()); }
Pass::Status BlockMergePass::Process() {
// Process all entry point functions.
ProcessFunction pfn = [this](Function* fp) { return MergeBlocks(fp); };
bool modified = context()->ProcessEntryPointCallTree(pfn);
return modified ? Status::SuccessWithChange : Status::SuccessWithoutChange;
}
BlockMergePass::BlockMergePass() = default;
} // namespace opt
} // namespace spvtools