[PATCH] D97397: [InstCombine] Add a combine for a shuffle of identical bitcasts

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp:2299
+      X->getType()->isVectorTy() &&
+      cast<FixedVectorType>(X->getType())->getNumElements() == VWidth &&
+      X->getType() == Y->getType()) {
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sanwou01 wrote:
> lebedev.ri wrote:
> > Can we do anything for the case where we have element count mismatches?
> Yes, I'm being fairly conservative here. I think the following example would be legal to transform similarly. Is that what you had in mind?
> 
> ```
> %0 = bitcast <4 x i32> %a to <4 x float>
> %1 = bitcast <2 x i32> %b to <2 x float>
> %2 = shufflevector <4 x float> %0, <2 x float> %1, <2 x i32> <i32 3, i32 5>
> ```
I actually don't have anything particular in mind, just asking.
That being said, i think both operands of a `shufflevector` must have the same type
(including vector element count), so i'm not sure that example works?


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https://reviews.llvm.org/D97397