[llvm] [AArch64][ISel] Remove zero instruction for `rev` all true predicates (PR #192925)

[Harry Ramsey via llvm-commits]

================
@@ -0,0 +1,116 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=aarch64-linux-gnu -mattr=+sve2p1 -verify-machineinstrs < %s | FileCheck %s
+
+define <vscale x 16 x i8> @test_revd_i8(<vscale x 16 x i8> %a) {
+; CHECK-LABEL: test_revd_i8:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    ptrue p0.b
+; CHECK-NEXT:    revd z0.q, p0/m, z0.q
----------------
Harry-Ramsey wrote:

Sorry, I shall do that going forward. Just for archive reasons this was the previous code generated for `rev`.

```
_revd_8(__SVUint8_t):
        movi    v1.2d, #0000000000000000
        ptrue   p0.b
        revd    z1.q, p0/m, z0.q
        mov     z0.d, z1.d
        ret
_revd_16(__SVUint16_t):
        movi    v1.2d, #0000000000000000
        ptrue   p0.h
        revd    z1.q, p0/m, z0.q
        mov     z0.d, z1.d
        ret
_revd_32(__SVUint32_t):
        movi    v1.2d, #0000000000000000
        ptrue   p0.s
        revd    z1.q, p0/m, z0.q
        mov     z0.d, z1.d
        ret
_revd_64(__SVUint64_t):
        movi    v1.2d, #0000000000000000
        ptrue   p0.d
        revd    z1.q, p0/m, z0.q
        mov     z0.d, z1.d
        ret
_revb_16(__SVUint16_t):
        movi    v1.2d, #0000000000000000
        ptrue   p0.h
        revb    z1.h, p0/m, z0.h
        mov     z0.d, z1.d
        ret
_revb_32(__SVUint32_t):
        movi    v1.2d, #0000000000000000
        ptrue   p0.s
        revb    z1.s, p0/m, z0.s
        mov     z0.d, z1.d
        ret
_revb_64(__SVUint64_t):
        movi    v1.2d, #0000000000000000
        ptrue   p0.d
        revb    z1.d, p0/m, z0.d
        mov     z0.d, z1.d
        ret
_revh_32(__SVUint32_t):
        movi    v1.2d, #0000000000000000
        ptrue   p0.s
        revh    z1.s, p0/m, z0.s
        mov     z0.d, z1.d
        ret
_revh_64(__SVUint64_t):
        movi    v1.2d, #0000000000000000
        ptrue   p0.d
        revh    z1.d, p0/m, z0.d
        mov     z0.d, z1.d
        ret
_revw_64(__SVUint64_t):
        movi    v1.2d, #0000000000000000
        ptrue   p0.d
        revw    z1.d, p0/m, z0.d
        mov     z0.d, z1.d
        ret
```

https://github.com/llvm/llvm-project/pull/192925