[PATCH] D148123: [AArch64][CostModel] Make sext/zext free if folded into a masked load

[David Sherwood via Phabricator via llvm-commits]

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Comment at: llvm/test/Analysis/CostModel/AArch64/masked_ldst.ll:113
 ; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction:   %load.nxv16i8 = call <vscale x 16 x i8> @llvm.masked.load.nxv16i8.p0(ptr undef, i32 8, <vscale x 16 x i1> undef, <vscale x 16 x i8> undef)
-; CHECK-NEXT: Cost Model: Found an estimated cost of 3 for instruction:   %zext.nxv16i8to16 = zext <vscale x 16 x i8> %load.nxv16i8 to <vscale x 16 x i16>
+; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction:   %zext.nxv16i8to16 = zext <vscale x 16 x i8> %load.nxv16i8 to <vscale x 16 x i16>
 ; CHECK-NEXT: Cost Model: Found an estimated cost of 1 for instruction:   %load.nxv8i8 = call <vscale x 8 x i8> @llvm.masked.load.nxv8i8.p0(ptr undef, i32 8, <vscale x 8 x i1> undef, <vscale x 8 x i8> undef)
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dmgreen wrote:
> Do you know why this has gone from 3 to 1, if the Dst type is not legal?  I think I would expect the score to be 2!
I assumed this was because it was deciding to create two legal extending loads and then stitch the results together, i.e. reinvoke getCastInstrCost with the type split in half.

  %load.nxv88.1 = call <vscale x 16 x i8> @llvm.masked.load.nxv8i8.p0(ptr undef, i32 8, <vscale x 8 x i1> undef, <vscale x 8 x i8> undef)
  %zext.nxv16i8to16.1 = zext <vscale x 8 x i8> %load.nxv8i8.1 to <vscale x 8 x i16>
  %load.nxv8i8.2 = call <vscale x 16 x i8> @llvm.masked.load.nxv8i8.p0(ptr undef, i32 8, <vscale x 8 x i1> undef, <vscale x 8 x i8> undef)
  %zext.nxv16i8to16.2 = zext <vscale x 8 x i8> %load.nxv8i8.2 to <vscale x 8 x i16>
  %zext.nxv16i8to16 = concat (%load.nxv8i8.1, %load.nxv8i8.2)

so that the only cost of the zext is just the concat, but it's a good question. I can double check.


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  https://reviews.llvm.org/D148123/new/

https://reviews.llvm.org/D148123