[llvm] [BOLT]Identify indirect call (PR #123305)

[Paschalis Mpeis via llvm-commits]

================
@@ -0,0 +1,47 @@
+## This test checks that indirect tail call is properly identified by BOLT on aarch64
+## when that OpDefCfaOffset=0 is in place without any stack changes between the 
+## CFI instruction and the indirect branch.
+
+# REQUIRES: system-linux
+
+# RUN: llvm-mc -filetype=obj -triple aarch64-unknown-unknown %s -o %t.o
+# RUN: %clang %cflags -O0 %t.o -o %t.exe -Wl,-q
+# RUN: llvm-bolt --print-all --print-only=indirect  \
+# RUN: %t.exe -o %t.bolt | FileCheck %s
+
+#CHECK: Binary Function "indirect" after building cfg {
+#CHECK-NOT: # UNKNOWN CONTROL FLOW
+#CHECK: End of Function "indirect"
+	.text
+	.global	indirect
+	.type	indirect, %function
+indirect:
+.LFB0:
+	.cfi_startproc
+	stp	x29, x30, [sp, -16]!
+	.cfi_def_cfa_offset 16
+	.cfi_offset 29, -16
+	.cfi_offset 30, -8
+	mov	w3, w1
+	add	w1, w0, w1
+	add	w5, w1, w1, lsr 31
+	tst	x1, 1
+	asr	w5, w5, 1
+	csel	w1, w1, w5, eq
+	cmp	w0, w3
+	beq	.L3
+	mov	w0, w3
+	mov	x16, x2
+	ldp	x29, x30, [sp], 16
+	.cfi_restore 30
+	.cfi_restore 29
+	.cfi_def_cfa_offset 0
+	mov w3, w1
+	add w1, w0, w1
+	br	x16
----------------
paschalis-mpeis wrote:

On your fist iteration you had a variant with no instructions between the CFI and the branch, but it has since been removed. It looked something like this:

```asm
...
	.cfi_def_cfa_offset 0
	br	x16
...
```

Could you add it back as another test (or another function in this test)?

Also do all the current instructions meaningfully contribute to this test? If not, could the assembly be further minimized by removing any instructions that don't add to the testing logic?

https://github.com/llvm/llvm-project/pull/123305