[PATCH] D71389: [ConstantFold][SVE] Fix constant folding for bitcast.

Thu Dec 12 11:54:53 PST 2019

huihuiz marked an inline comment as done.
huihuiz added a comment.

In D71389#1781620 <https://reviews.llvm.org/D71389#1781620>, @spatel wrote:

> LGTM. I don't know how many of these patches are needed, but it would be slightly more efficient to create a "vscale.ll" test file and put all of the related tests in that 1 file.

Thank you Sanjay!
Yes, I will try my best to combine them. The current code base has a lot of assumption based on fixed length vector.
I am going through the IR passes, and try to fix them to the best I can.

================
Comment at: llvm/lib/IR/ConstantFold.cpp:52
+  // compile-time.
+  if (DstTy->isScalable())
+    return nullptr;
----------------
sdesmalen wrote:
> Do we want to add support for a special case here for splat operations (like the one in the test)?
Actually we can not, we will end up in scalable vector constant. 
Instead of <4 x i32> <i32 1, i32 1, i32 1, i32 1>, we will need a form like "<vscale x 4 x i32> [?]"

I don't know how to express scalable vector constant in current upstream, please let me know if I get anything wrong?

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