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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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49
SPIRV/SpvPostProcess.cpp
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@@ -39,6 +39,7 @@
#include <cassert>
#include <cstdlib>
#include <unordered_map>
#include <unordered_set>
#include <algorithm>
@@ -319,16 +320,14 @@ void Builder::postProcess(Instruction& inst)
}
}
// Called for each instruction in a reachable block.
void Builder::postProcessReachable(const Instruction&)
{
// did have code here, but questionable to do so without deleting the instructions
}
// comment in header
void Builder::postProcess()
{
// reachableBlocks is the set of blockss reached via control flow, or which are
// unreachable continue targert or unreachable merge.
std::unordered_set<const Block*> reachableBlocks;
std::unordered_map<Block*, Block*> headerForUnreachableContinue;
std::unordered_set<Block*> unreachableMerges;
std::unordered_set<Id> unreachableDefinitions;
// Collect IDs defined in unreachable blocks. For each function, label the
// reachable blocks first. Then for each unreachable block, collect the
@@ -336,16 +335,41 @@ void Builder::postProcess()
for (auto fi = module.getFunctions().cbegin(); fi != module.getFunctions().cend(); fi++) {
Function* f = *fi;
Block* entry = f->getEntryBlock();
inReadableOrder(entry, [&reachableBlocks](const Block* b) { reachableBlocks.insert(b); });
inReadableOrder(entry,
[&reachableBlocks, &unreachableMerges, &headerForUnreachableContinue]
(Block* b, ReachReason why, Block* header) {
reachableBlocks.insert(b);
if (why == ReachDeadContinue) headerForUnreachableContinue[b] = header;
if (why == ReachDeadMerge) unreachableMerges.insert(b);
});
for (auto bi = f->getBlocks().cbegin(); bi != f->getBlocks().cend(); bi++) {
Block* b = *bi;
if (reachableBlocks.count(b) == 0) {
for (auto ii = b->getInstructions().cbegin(); ii != b->getInstructions().cend(); ii++)
if (unreachableMerges.count(b) != 0 || headerForUnreachableContinue.count(b) != 0) {
auto ii = b->getInstructions().cbegin();
++ii; // Keep potential decorations on the label.
for (; ii != b->getInstructions().cend(); ++ii)
unreachableDefinitions.insert(ii->get()->getResultId());
} else if (reachableBlocks.count(b) == 0) {
// The normal case for unreachable code. All definitions are considered dead.
for (auto ii = b->getInstructions().cbegin(); ii != b->getInstructions().cend(); ++ii)
unreachableDefinitions.insert(ii->get()->getResultId());
}
}
}
// Modify unreachable merge blocks and unreachable continue targets.
// Delete their contents.
for (auto mergeIter = unreachableMerges.begin(); mergeIter != unreachableMerges.end(); ++mergeIter) {
(*mergeIter)->rewriteAsCanonicalUnreachableMerge();
}
for (auto continueIter = headerForUnreachableContinue.begin();
continueIter != headerForUnreachableContinue.end();
++continueIter) {
Block* continue_target = continueIter->first;
Block* header = continueIter->second;
continue_target->rewriteAsCanonicalUnreachableContinue(header);
}
// Remove unneeded decorations, for unreachable instructions
decorations.erase(std::remove_if(decorations.begin(), decorations.end(),
[&unreachableDefinitions](std::unique_ptr<Instruction>& I) -> bool {
@@ -374,13 +398,6 @@ void Builder::postProcess()
}
}
// process all reachable instructions...
for (auto bi = reachableBlocks.cbegin(); bi != reachableBlocks.cend(); ++bi) {
const Block* block = *bi;
const auto function = [this](const std::unique_ptr<Instruction>& inst) { postProcessReachable(*inst.get()); };
std::for_each(block->getInstructions().begin(), block->getInstructions().end(), function);
}
// process all block-contained instructions
for (auto fi = module.getFunctions().cbegin(); fi != module.getFunctions().cend(); fi++) {
Function* f = *fi;