[llvm] [LLVM][InstCombine] Enable constant folding for SVE asr,lsl and lsr intrinsics. (PR #137350)

[Paul Walker via llvm-commits]

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@@ -1571,7 +1583,11 @@ simplifySVEIntrinsicBinOp(InstCombiner &IC, IntrinsicInst &II,
   else
     SimpleII = simplifyBinOp(Opc, Op1, Op2, DL);
 
-  if (!SimpleII)
+  // An SVE intrinsic's result is always defined. However, this is not the case
+  // for its equivalent IR instruction (e.g. when shifting by an amount more
+  // than the data's bitwidth). Simplifications to an undefined result must be
+  // ignored to preserve the intrinsic's expected behaviour.
+  if (!SimpleII || isa<UndefValue>(SimpleII))
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paulwalker-arm wrote:

I've been thinking about this some more and I'm now leaning towards saying the SVE intrinsics should not propagate poison in general.  Whilst the IR is fully define in this respect the SVE ACLE is not and I think some of the IR's outcomes would not match ACLE writer expectations. 

https://github.com/llvm/llvm-project/pull/137350