[PATCH] D113141: [InstCombine] Relax and reorganize one use checks in the ~(a | b) & c

[Stanislav Mekhanoshin via Phabricator via llvm-commits]

rampitec added inline comments.


================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp:2815
     // (~(A | B) & C) | ~(A | C) --> ~((B & C) | A)
-    if (match(Op1, m_Not(m_c_Or(m_Specific(A), m_Specific(C)))))
+    if (match(Op1, m_OneUse(m_Not(m_c_Or(m_Specific(A), m_Specific(C))))))
       return BinaryOperator::CreateNot(
----------------
spatel wrote:
> This isn't strong enough to prevent the transform from ending up with more instructions than we started with - we are creating 3 instructions, so we need to eliminate at least 2 intermediate values plus the final value. 
> 
> I think we'd be ok if we have 2 m_OneUse checks in this match (similar to the transform above this).
> 
> Please add a test like this to confirm:
> 
> ```
> define i32 @or_and_not_not_2_extra_uses(i32 %a, i32 %b, i32 %c) {
>   %or1 = or i32 %b, %a
>   call void @use(i32 %or1)
>   %not1 = xor i32 %or1, -1
>   %or2 = or i32 %a, %c
>   %not2 = xor i32 %or2, -1
>   %and = and i32 %not2, %b
>   call void @use(i32 %and)
>   %or3 = or i32 %not1, %and
>   ret i32 %or3
> }
> 
> ```
Thanks for the catch!


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  https://reviews.llvm.org/D113141/new/

https://reviews.llvm.org/D113141