[llvm-dev] ConstantFoldTerminator doesn't delete trivially dead phi inputs (original) (raw)
Johannes Doerfert via llvm-dev llvm-dev at lists.llvm.org
Fri May 15 10:45:39 PDT 2020
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On 5/15/20 5:57 AM, Jay Foad via llvm-dev wrote:
I'm looking into some missed optimizations where CodeGenPrepare seems to leave trivially dead instructions lying around.
This happens because CodeGenPrepare::runOnFunction calls ConstantFoldTerminator which folds a "br i1 false" into an unconditional branch and calls BasicBlock::removePredecessor which calls PHINode::removeIncomingValue. Each incoming value that is removed from a phi node might be dead now, but nothing deletes them. Is there any way this could be improved? Could PHINode::removeIncomingValue call RecursivelyDeleteTriviallyDeadInstructions on the value it removes, or is that a layering violation? Any other ideas?
I think this is certainly a desirable behavior that could be opt-in
for ConstantFoldTerminator.
Thanks, Jay.
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