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https://github.com/c64scene-ar/llvm-6502.git
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LLVM backend for 6502
a2b88163af
smaller integer loads and stores. The high-level motivation is that the frontend sometimes generates a single whole-alloca integer load or store during ABI lowering of splittable allocas. We need to be able to break this apart in order to see the underlying elements and properly promote them to SSA values. The hope is that this fixes some performance regressions on x86-32 with the new SROA pass. Unfortunately, this causes quite a bit of churn in the test cases, and bloats some IR that comes out. When we see an alloca that consists soley of bits and bytes being extracted and re-inserted, we now do some splitting first, before building widened integer "bucket of bits" representations. These are always well folded by instcombine however, so this shouldn't actually result in missed opportunities. If this splitting of all-integer allocas does cause problems (perhaps due to smaller SSA values going into the RA), we could potentially go to some extreme measures to only do this integer splitting trick when there are non-integer component accesses of an alloca, but discovering this is quite expensive: it adds yet another complete walk of the recursive use tree of the alloca. Either way, I will be watching build bots and LNT bots to see what fallout there is here. If anyone gets x86-32 numbers before & after this change, I would be very interested. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166662 91177308-0d34-0410-b5e6-96231b3b80d8 |
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| README.txt | ||
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