While debugging GVNHoist, I found it confusing that the entries in a
VNtoInsns were not always value numbers. They _usually_ were except for
StoreInst in which case they were a hash of two different value numbers.
This leads to two observations:
- It is more difficult to debug things when the semantic contents of
VNtoInsns changes over time.
- Using a single value number is not much cheaper, the value of
VNtoInsns is a SmallVector.
- It is not immediately clear what the algorithm would do if there were
hash collisions in the StoreInst case.
Using a DenseMap of std::pair sidesteps all of this.
N.B. The changes in the test were due their sensitivity to the
iteration order of VNtoInsns which has changed.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@275761 91177308-0d34-0410-b5e6-96231b3b80d8
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