[llvm] [InitUndef] Enable the InitUndef pass on non-AMDGPU targets (PR #108353)

[Matt Arsenault via llvm-commits]

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@@ -0,0 +1,44 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
+# RUN: llc -mtriple=aarch64-- -run-pass=init-undef -o - %s | FileCheck %s
+
+--- |
+  define dso_local i32 @test_stxp_undef(ptr %p, i64 %x) #0 {
+    %res = call i32 @llvm.aarch64.stxp(i64 undef, i64 %x, ptr %p)
+    ret i32 %res
+  }
+
+...
+---
+name:            test_stxp_undef
+alignment:       4
+tracksRegLiveness: true
+registers:
+  - { id: 0, class: gpr64common }
+  - { id: 1, class: gpr64 }
+  - { id: 2, class: gpr32 }
+  - { id: 3, class: gpr64 }
+liveins:
+  - { reg: '$x0', virtual-reg: '%0' }
+  - { reg: '$x1', virtual-reg: '%1' }
+body:             |
+  bb.0 (%ir-block.0):
+    liveins: $x0, $x1
+
+    ; CHECK-LABEL: name: test_stxp_undef
+    ; CHECK: liveins: $x0, $x1
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:gpr64 = COPY $x1
+    ; CHECK-NEXT: [[COPY1:%[0-9]+]]:gpr64common = COPY $x0
+    ; CHECK-NEXT: [[DEF:%[0-9]+]]:gpr64 = IMPLICIT_DEF
+    ; CHECK-NEXT: [[INIT_UNDEF:%[0-9]+]]:gpr64 = INIT_UNDEF
+    ; CHECK-NEXT: early-clobber %2:gpr32 = STXPX killed [[INIT_UNDEF]], [[COPY]], [[COPY1]] :: (volatile store (s128) into %ir.p)
+    ; CHECK-NEXT: $w0 = COPY %2
+    ; CHECK-NEXT: RET_ReallyLR implicit $w0
+    %1:gpr64 = COPY $x1
+    %0:gpr64common = COPY $x0
+    %3:gpr64 = IMPLICIT_DEF
+    early-clobber %2:gpr32 = STXPX killed %3, %1, %0 :: (volatile store (s128) into %ir.p)
----------------
arsenm wrote:

```suggestion
    early-clobber %2:gpr32 = STXPX killed %3, %1, %0 :: (volatile store (s128))
```

https://github.com/llvm/llvm-project/pull/108353