[PATCH] D118617: [AArch64][SVE] Remove false register dependency for unary FP convert operations

[Bradley Smith via Phabricator via llvm-commits]

bsmith added inline comments.


================
Comment at: llvm/lib/Target/AArch64/AArch64SVEInstrInfo.td:1685
   // Floating-point -> signed integer
-  def : Pat<(nxv2f16 (AArch64scvtf_mt (nxv2i1 PPR:$Pg),
+  def : Pat<(nxv2f16 (AArch64scvtf_mt (nxv2i1 (SVEAllActive):$Pg),
                       (sext_inreg (nxv2i64 ZPR:$Zs), nxv2i16), (nxv2f16 ZPR:$Zd))),
----------------
I don't believe converting these patterns like this is ok, some of the intrinsics (such as `@llvm.aarch64.sve.scvtf`) can get lowered to these nodes without an all active predicate. With this patch I believe a case such as the below will either regress or fail to select.

```
define <vscale x 8 x half> @scvtf_f16_i16(<vscale x 8 x half> %a, <vscale x 8 x i1> %pg, <vscale x 8 x i16> %b) {
    %out = call <vscale x 8 x half> @llvm.aarch64.sve.scvtf.nxv8f16.nxv8i16(<vscale x 8 x half> %a,<vscale x 8 x i1> %pg, <vscale x 8 x i16> %b)
   ret <vscale x 8 x half> %out
}

declare <vscale x 8 x half> @llvm.aarch64.sve.scvtf.nxv8f16.nxv8i16(<vscale x 8 x half>, <vscale x 8 x i1>, <vscale x 8 x i16>)
```


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D118617/new/

https://reviews.llvm.org/D118617