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(parent: d09ac03) | patch
[DAGCombiner] `~(add X, -1)` -> `neg X` fold
authorRoman Lebedev <lebedev.ri@gmail.com>
Fri, 3 Jan 2020 13:01:16 +0000 (16:01 +0300)
committerRoman Lebedev <lebedev.ri@gmail.com>
Fri, 3 Jan 2020 14:55:46 +0000 (17:55 +0300)
commit86403c0ff8930e6d4d21d94baa7384e54620f4cf
tree1c7ff062ffac1b7ea3fbf5e737237e20a37ada7ctree | snapshot
parentd09ac032ee0012d11ae9f9d717eaa6a10cc22a75commit | diff
[DAGCombiner] `~(add X, -1)` -> `neg X` fold

The fold 'A - (A & (B - 1))' -> 'A & (0 - B)'
added in 8dab0a4a7d691f2704f1079538e0ef29548db159
is too specific. It should just be 'A - (A & B)' -> 'A & (~B)',
but we currently fail to sink that '~' into `(B - 1)`.

Name: ~(X - 1)  ->  (0 - X)
%o = add i32 %X, -1
%r = xor i32 %o, -1
  =>
%r = sub i32 0, %X

https://rise4fun.com/Alive/rjU
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp diff | blob | history
llvm/test/CodeGen/X86/not-of-dec.ll diff | blob | history
Domain: System / Toolchain;