[llvm-commits] Patch: instcombine on overflow intrinsics

[Alastair Lynn]

Hello-

This patch adds the follow to instcombine:
   overflow intrinsic (undef, X) or overflow intrinsic (X, undef) ->  
undef
   add overflow (X, 0) or add overflow (0, X) -> {X, false}
   unsigned add overflow (X, Y) -> {X + Y, true} where the HO bit is  
provably 1 in both X and Y
   unsigned add overflow (X, Y) -> {X + Y, false} where the HO bit is  
provably 0 in both X and Y
   sub overflow (X, 0) -> {X, false}
   mul overflow (X, 0) -> {0, false}
   mul overflow (X, 1) -> {X, false}

Testcase in patch.

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