[llvm] [MachineLICM] Workaround - apply RegMasks conservatively (PR #95926)

[Jay Foad via llvm-commits]

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@@ -0,0 +1,49 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
+# RUN: llc -mtriple=aarch64-unknown-linux-gnu -run-pass=greedy,machinelicm -verify-machineinstrs -debug -o - %s | FileCheck %s
+
+# FIXME: Running RA is needed otherwise it runs pre-RA LICM.
+---
+name: test
+tracksRegLiveness: true
+body: |
+  ; CHECK-LABEL: name: test
+  ; CHECK: bb.0:
+  ; CHECK-NEXT:   successors: %bb.1(0x80000000)
+  ; CHECK-NEXT:   liveins: $x0, $w1, $x2
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   B %bb.1
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.1:
+  ; CHECK-NEXT:   successors: %bb.1(0x40000000), %bb.2(0x40000000)
+  ; CHECK-NEXT:   liveins: $x0, $w1, $x2
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   renamable $q11 = MOVIv4i32 2, 8
+  ; CHECK-NEXT:   BL &memset, csr_aarch64_aapcs, implicit-def dead $lr, implicit $sp, implicit $x0, implicit $w1, implicit $x2, implicit-def $sp, implicit-def $x0
+  ; CHECK-NEXT:   renamable $q10 = MVNIv4i32 4, 0
----------------
jayfoad wrote:

What does this test actually demonstrate? Without this patch, I see that the def of `q10` gets hoisted past this memset call:
```
BL &memset, <regmask $fp $lr $wzr $xzr $b8 $b9 $b10 $b11 $b12 $b13 $b14 $b15 $d8 $d9 $d10 $d11 $d12 $d13 $d14 $d15 $h8 $h9 $h10 $h11 
$h12 $h13 $h14 $h15 $s8 $s9 $s10 $s11 $s12 $s13 $s14 $s15 $w19 $w20 $w21 $w22 $w23 $w24 $w25 $w26 $w27 $w28 $w29 $w30 $x19 $x20 $x21 $x22 $x23 
$x24 $x25 $x26 $x27 $x28 $d8_d9 $d9_d10 $d10_d11 $d11_d12 $d12_d13 $d13_d14 $d14_d15 $d8_d9_d10_d11 $d9_d10_d11_d12 $d10_d11_d12_d13 $d11_d12_d
13_d14 $d12_d13_d14_d15 $d8_d9_d10 $d9_d10_d11 $d10_d11_d12 $d11_d12_d13 $d12_d13_d14 $d13_d14_d15 $x22_x23_x24_x25_x26_x27_x28_fp $x20_x21_x22
_x23_x24_x25_x26_x27 $w20_w21 $w22_w23 $w24_w25 $w26_w27 $w28_w29 $x28_fp $x20_x21 $x22_x23 $x24_x25 $x26_x27>, implicit-def dead $lr, implicit
 $sp, implicit $x0, implicit $w1, implicit $x2, implicit-def $sp, implicit-def $x0
```
I don't understand why this happened. `q10` has subregs `d20` and `d21` but I don't see any of those listed in this regmask.

https://github.com/llvm/llvm-project/pull/95926