[BOLT] Testcase to repro R_X86_64_REX_GOTPCRELX bug

Add a new testcase that reproduces a bug when BOLTing current
trunk LLD bootstrapped with trunk clang. This makes it official
that we do not support this transformation but are working on
it. When the support is ready, XFAIL should be removed.

Reviewed By: maksfb, Amir, yota9

Differential Revision: https://reviews.llvm.org/D125843

bolt/test/X86/gotpcrelx.s

@@ -0,0 +1,54 @@
+# This reproduces a bug with misinterpreting the gotpcrelx reloc
+
+# Here we use llvm-mc -relax-relocations to produce R_X86_64_REX_GOTPCRELX
+# and ld.lld to consume it and optimize it, transforming a CMP <mem, reg>
+# into CMP <imm, reg>.
+# Then we check that BOLT updates correctly the imm operand that references
+# a function address. Currently XFAIL as we do not support it.
+
+# REQUIRES: system-linux
+# XFAIL: *
+
+# RUN: llvm-mc -filetype=obj -triple x86_64-unknown-linux \
+# RUN:   -relax-relocations %s -o %t.o
+# RUN: llvm-strip --strip-unneeded %t.o
+# RUN: ld.lld %t.o -o %t.exe -q
+# RUN: llvm-readobj -r %t.exe | FileCheck --check-prefix=READOBJ %s
+# RUN: llvm-bolt %t.exe -relocs -o %t.out -lite=0
+# RUN: llvm-objdump -d --no-show-raw-insn --print-imm-hex \
+# RUN:   %t.out | FileCheck --check-prefix=DISASM %s
+
+# Check that R_X86_64_REX_GOTPCRELX is present in the input binary
+# READOBJ: 0x[[#%X,]] R_X86_64_REX_GOTPCRELX foo 0x[[#%X,]]
+
+# DISASM:      Disassembly of section .text:
+# DISASM-EMPTY:
+# DISASM-NEXT: <_start>:
+# DISASM-NEXT:                 leaq  0x[[#%x,ADDR:]], %rax
+# DISASM-NEXT:                 cmpq  0x[[#ADDR]], %rax
+
+  .text
+  .globl _start
+  .type _start, %function
+_start:
+  .cfi_startproc
+  leaq foo, %rax
+  cmpq foo@GOTPCREL(%rip), %rax
+  je  b
+c:
+  mov $1, %rdi
+  callq foo
+b:
+  xorq %rdi, %rdi
+  callq foo
+  ret
+  .cfi_endproc
+  .size _start, .-_start
+
+  .globl foo
+  .type foo, %function
+foo:
+  .cfi_startproc
+  ret
+  .cfi_endproc
+  .size foo, .-foo