[CodeGen] Add test for PR53990 (NFC)

(cherry picked from commit e075bf6)

Author: nikic

llvm/test/CodeGen/X86/pr53990-incorrect-machine-sink.ll

@@ -0,0 +1,67 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=x86_64-- < %s | FileCheck %s
+
+declare void @clobber()
+
+define void @test(i1 %c, i64* %p, i64* noalias %p2) nounwind {
+; CHECK-LABEL: test:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    pushq %rbp
+; CHECK-NEXT:    pushq %r15
+; CHECK-NEXT:    pushq %r14
+; CHECK-NEXT:    pushq %rbx
+; CHECK-NEXT:    pushq %rax
+; CHECK-NEXT:    movq %rdx, %rbx
+; CHECK-NEXT:    movq %rsi, %r14
+; CHECK-NEXT:    movl %edi, %r15d
+; CHECK-NEXT:    xorl %eax, %eax
+; CHECK-NEXT:    jmpq *.LJTI0_0(,%rax,8)
+; CHECK-NEXT:  .LBB0_1: # %split.3
+; CHECK-NEXT:    movq (%r14), %rbp
+; CHECK-NEXT:    testb $1, %r15b
+; CHECK-NEXT:    je .LBB0_3
+; CHECK-NEXT:  # %bb.2: # %clobber
+; CHECK-NEXT:    callq clobber@PLT
+; CHECK-NEXT:  .LBB0_3: # %sink
+; CHECK-NEXT:    movq %rbp, (%rbx)
+; CHECK-NEXT:  .LBB0_4: # %latch
+; CHECK-NEXT:    # =>This Inner Loop Header: Depth=1
+; CHECK-NEXT:    xorl %eax, %eax
+; CHECK-NEXT:    jmpq *.LJTI0_0(,%rax,8)
+entry:
+  %val = load i64, i64* %p, align 8
+  br label %loop
+
+loop:
+  switch i8 undef, label %unreachable [
+    i8 0, label %latch
+    i8 1, label %split.1
+    i8 2, label %split.2
+    i8 3, label %split.3
+  ]
+
+unreachable:
+  unreachable
+
+split.3:
+  br i1 %c, label %clobber, label %sink
+
+split.1:
+  br label %latch
+
+split.2:
+  br label %latch
+
+clobber:
+  call void @clobber()
+  br label %sink
+
+sink:
+  store i64 %val, i64* %p2, align 8
+  br label %latch
+
+latch:
+  %phi = phi i64 [ 0, %sink ], [ 0, %split.2 ], [ 1, %split.1 ], [ 0, %loop ]
+  %phi.live = add i64 %phi, 0
+  br label %loop
+}