[llvm] [ConstantFolding] Fold scalable get_active_lane_masks (PR #156659)

[Matthew Devereau via llvm-commits]

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@@ -4238,6 +4238,13 @@ static Constant *ConstantFoldScalableVectorCall(
 
     return ConstantInt::getFalse(SVTy);
   }
+  case Intrinsic::get_active_lane_mask: {
+    auto Op0 = cast<ConstantInt>(Operands[0])->getValue();
+    auto Op1 = cast<ConstantInt>(Operands[1])->getValue();
+    if ((Op0.uge(Op1) && (!Op1.isZero())))
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MDevereau wrote:

@paulwalker-arm Thanks. What I gather from that is it's now OK to assume active_lane_mask(0, 0) is an all false predicate just as active_lane_mask(3, 3) is and that no further changes are needed in this PR.

https://github.com/llvm/llvm-project/pull/156659