[all-commits] [llvm/llvm-project] fee295: [ARM] Fix for undef elements from demanded element...

[David Green via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: fee2953f23bd8a8a71e574e6a8db08033778d3a4
      https://github.com/llvm/llvm-project/commit/fee2953f23bd8a8a71e574e6a8db08033778d3a4
  Author: David Green <david.green at arm.com>
  Date:   2023-11-02 (Thu, 02 Nov 2023)

  Changed paths:
    M llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp
    M llvm/test/Transforms/InstCombine/ARM/mve-narrow.ll

  Log Message:
  -----------
  [ARM] Fix for undef elements from demanded elements (#70504)

I think this is right, that the undef bits should be the undef bits from
the passthrough (operand 0), with the top/bottom lanes cleared, as they
come from the second arg (operand 1). We don't yet attempt to look for
undef elements in the second operand, but this should fix the bug with
all elements being marked as undef and the instruction being optimized
away.