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eliminate_dead_code in place

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Not too tricky, and saves a program copy.

Change-Id: I3f7e97c1f1935df50905b6cc1ee4de33da2148ae
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/281285
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
This commit is contained in:
Mike Klein 2020-04-02 14:25:56 -05:00 committed by Skia Commit-Bot
parent 17fbcd145b
commit 5384f4036f
1 changed files with 23 additions and 16 deletions
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39
src/core/SkVM.cpp
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@ -478,16 +478,16 @@ namespace skvm {
return program;
}
std::vector<Instruction> eliminate_dead_code(const std::vector<Instruction> program) {
std::vector<Instruction> eliminate_dead_code(std::vector<Instruction> program) {
// Determine which Instructions are live by working back from side effects.
std::vector<bool> live(program.size(), false);
auto mark_live = [&](Val id, auto& recurse) -> void {
if (live[id] == false) {
live[id] = true;
Instruction inst = program[id];
if (inst.x != NA) { recurse(inst.x, recurse); }
if (inst.y != NA) { recurse(inst.y, recurse); }
if (inst.z != NA) { recurse(inst.z, recurse); }
for (Val arg : {inst.x, inst.y, inst.z}) {
if (arg != NA) { recurse(arg, recurse); }
}
}
};
for (Val id = 0; id < (Val)program.size(); id++) {
@ -496,22 +496,29 @@ namespace skvm {
}
}
// Construct a new program with only live Instructions.
std::vector<Instruction> only_live;
only_live.reserve(program.size());
// Rewrite the program with only live Instructions:
// - remap IDs in live Instructions to what they'll be once dead Instructions are removed;
// - then actually remove the dead Instructions.
std::vector<Val> new_id(program.size(), NA);
for (Val id = 0; id < (Val)program.size(); id++) {
for (Val id = 0, next = 0; id < (Val)program.size(); id++) {
if (live[id]) {
Instruction inst = program[id];
if (inst.x != NA) { inst.x = new_id[inst.x]; SkASSERT(inst.x != NA); }
if (inst.y != NA) { inst.y = new_id[inst.y]; SkASSERT(inst.y != NA); }
if (inst.z != NA) { inst.z = new_id[inst.z]; SkASSERT(inst.z != NA); }
new_id[id] = (Val)only_live.size();
only_live.push_back(inst);
Instruction& inst = program[id];
for (Val* arg : {&inst.x, &inst.y, &inst.z}) {
if (*arg != NA) {
*arg = new_id[*arg];
SkASSERT(*arg != NA);
}
}
new_id[id] = next++;
}
}
return only_live;
auto it = std::remove_if(program.begin(), program.end(), [&](const Instruction& inst) {
Val id = (Val)(&inst - program.data());
return !live[id];
});
program.erase(it, program.end());
return program;
}
std::vector<Instruction> schedule(const std::vector<Instruction> program) {