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Optimize tree walking in markAliveBlocks.

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Check whether a BB is known as reachable before adding it to the worklist.
This way BB's with multiple predecessors are added to the list no more than
once.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@170335 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evgeniy Stepanov 2012-12-17 14:28:00 +00:00
parent a839ffc323
commit 1794814198
1 changed files with 3 additions and 4 deletions
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7
lib/Transforms/Scalar/SimplifyCFGPass.cpp
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@ -111,13 +111,11 @@ static bool markAliveBlocks(BasicBlock *BB,
SmallVector<BasicBlock*, 128> Worklist;
Worklist.push_back(BB);
Reachable.insert(BB);
bool Changed = false;
do {
BB = Worklist.pop_back_val();
if (!Reachable.insert(BB))
continue;
// Do a quick scan of the basic block, turning any obviously unreachable
// instructions into LLVM unreachable insts. The instruction combining pass
// canonicalizes unreachable insts into stores to null or undef.
@ -176,7 +174,8 @@ static bool markAliveBlocks(BasicBlock *BB,
Changed |= ConstantFoldTerminator(BB, true);
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
Worklist.push_back(*SI);
if (Reachable.insert(*SI))
Worklist.push_back(*SI);
} while (!Worklist.empty());
return Changed;
}