[llvm-commits] ScalarEvolution fix for treeadd

[Nick Lewycky]

Treeadd has a for loop from 0 to 100 that scalar-evolution isn't able to
determine the bounds of. Attached is a patch that handles the unusual
case where the exit branch indirectly leads back to the loop header.

It didn't cause any miscompiles in llvm-test (excl. External) and I did
a count of how many loops it was able to predict before and after this
patch:

Before:

predictable loop count: 4904 (21%)
not predictable: 18359       (79%)

After:

predictable loop count: 4679 (24%)
not predictable: 14877       (76%)

The total varies because the loop optimizations must request the loop
count from scalar evolution. It's not clear to me why -- perhaps the
loops were canonicalized earlier.

Nick
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