[PATCH] D148275: [InstCombine] support fold select(X|Y,X|Y,X) to X|Y

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


================
Comment at: llvm/lib/Analysis/InstructionSimplify.cpp:4588
+    Value *Y;
+    // select(X | Y == 0, X or Y, X | Y) -> X | Y
+    if (match(CondVal, m_ICmp(Pred, m_Specific(FalseVal), m_Zero())) &&
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HerrCai0907 wrote:
> goldstein.w.n wrote:
> > You could also do:
> > `select(X | Y == X, X, X | Y)` -> `X | Y`
> > and
> > `select (X|Y == Y, Y, X|Y)` -> `X|Y`
> > https://alive2.llvm.org/ce/z/hawAog
> I think it can be done in next patch
We already handle this case using generic select equivalence replacement. The only reason we need this patch is that the select replacement needs to follow the implication `X | Y == 0 => X == 0`. (We could generalize the generic code to do that, but I'm fine with keeping it as a special case for now.)


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  https://reviews.llvm.org/D148275/new/

https://reviews.llvm.org/D148275