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SPIR-V: Aggressively prune unreachable merge, continue target

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More aggressively prune unreachable code as follows.
When no control flow edges reach a merge block or continue target:
- delete their contents so that:
  - a merge block becomes OpLabel, then OpUnreachable
  - a continue target becomes OpLabel, then an OpBranch back to the
    loop header
- any basic block which is dominated by such a merge block or continue
  target is removed as well.
- decorations targeting the removed instructions are removed.

Enables the SPIR-V builder post-processing step the GLSLANG_WEB case.
This commit is contained in:
David Neto
2019-10-21 14:50:31 -04:00
parent b131630e7c
commit 8c3d5b4b6c
44 changed files with 2398 additions and 1423 deletions
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44
SPIRV/InReadableOrder.cpp
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@@ -61,17 +61,22 @@ namespace {
// Use by calling visit() on the root block.
class ReadableOrderTraverser {
public:
explicit ReadableOrderTraverser(std::function<void(Block*)> callback) : callback_(callback) {}
ReadableOrderTraverser(std::function<void(Block*, spv::ReachReason, Block*)> callback)
: callback_(callback) {}
// Visits the block if it hasn't been visited already and isn't currently
// being delayed. Invokes callback(block), then descends into its
// being delayed. Invokes callback(block, why, header), then descends into its
// successors. Delays merge-block and continue-block processing until all
// the branches have been completed.
void visit(Block* block)
// the branches have been completed. If |block| is an unreachable merge block or
// an unreachable continue target, then |header| is the corresponding header block.
void visit(Block* block, spv::ReachReason why, Block* header)
{
assert(block);
if (why == spv::ReachViaControlFlow) {
reachableViaControlFlow_.insert(block);
}
if (visited_.count(block) || delayed_.count(block))
return;
callback_(block);
callback_(block, why, header);
visited_.insert(block);
Block* mergeBlock = nullptr;
Block* continueBlock = nullptr;
@@ -87,27 +92,40 @@ public:
delayed_.insert(continueBlock);
}
}
const auto successors = block->getSuccessors();
for (auto it = successors.cbegin(); it != successors.cend(); ++it)
visit(*it);
if (why == spv::ReachViaControlFlow) {
const auto& successors = block->getSuccessors();
for (auto it = successors.cbegin(); it != successors.cend(); ++it)
visit(*it, why, nullptr);
}
if (continueBlock) {
const spv::ReachReason continueWhy =
(reachableViaControlFlow_.count(continueBlock) > 0)
? spv::ReachViaControlFlow
: spv::ReachDeadContinue;
delayed_.erase(continueBlock);
visit(continueBlock);
visit(continueBlock, continueWhy, block);
}
if (mergeBlock) {
const spv::ReachReason mergeWhy =
(reachableViaControlFlow_.count(mergeBlock) > 0)
? spv::ReachViaControlFlow
: spv::ReachDeadMerge;
delayed_.erase(mergeBlock);
visit(mergeBlock);
visit(mergeBlock, mergeWhy, block);
}
}
private:
std::function<void(Block*)> callback_;
std::function<void(Block*, spv::ReachReason, Block*)> callback_;
// Whether a block has already been visited or is being delayed.
std::unordered_set<Block *> visited_, delayed_;
// The set of blocks that actually are reached via control flow.
std::unordered_set<Block *> reachableViaControlFlow_;
};
}
void spv::inReadableOrder(Block* root, std::function<void(Block*)> callback)
void spv::inReadableOrder(Block* root, std::function<void(Block*, spv::ReachReason, Block*)> callback)
{
ReadableOrderTraverser(callback).visit(root);
ReadableOrderTraverser(callback).visit(root, spv::ReachViaControlFlow, nullptr);
}