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robust. It now uses an InstVisitor and worklist to actually walk the uses of the Alloca transitively and detect the pattern which we can directly promote: loads & stores of the whole alloca and instructions we can completely ignore. Also, with this new implementation teach both the predicate for testing whether we can promote and the promotion engine itself to use the same code so we no longer have strange divergence between the two code paths. I've added some silly test cases to demonstrate that we can handle slightly more degenerate code patterns now. See the below for why this is even interesting. Performance impact: roughly 1% regression in the performance of SROA or ScalarRepl on a large C++-ish test case where most of the allocas are basically ready for promotion. The reason is because of silly redundant work that I've left FIXMEs for and which I'll address in the next commit. I wanted to separate this commit as it changes the behavior. Once the redundant work in removing the dead uses of the alloca is fixed, this code appears to be faster than the old version. =] So why is this useful? Because the previous requirement for promotion required a *specific* visit pattern of the uses of the alloca to verify: we *had* to look for no more than 1 intervening use. The end goal is to have SROA automatically detect when an alloca is already promotable and directly hand it to the mem2reg machinery rather than trying to partition and rewrite it. This is a 25% or more performance improvement for SROA, and a significant chunk of the delta between it and ScalarRepl. To get there, we need to make mem2reg actually capable of promoting allocas which *look* promotable to SROA without have SROA do tons of work to massage the code into just the right form. This is actually the tip of the iceberg. There are tremendous potential savings we can realize here by de-duplicating work between mem2reg and SROA. llvm-svn: 187191 |
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