[BOLT] Add test case triggering JT assertion

[rafauler]

Summary

Current case that triggers BOLT assertion. Marked XFAIL.
In this test case, we reproduce the behavior seen in gcc where the
base address of a jump table is decremented by some number and ends up
at the exact addess of a jump table from another function. After
linking, the instruction references another jump table and that
confuses BOLT.

[rafauler]

Add XFAIL. Expand intro.

[aeubanks]

this test unexpectedly passes in non-assert builds of bolt, causing check-bolt to fail

[aeubanks]

59bc64c667f3e1fb724a4180ed2e6c78857d918e

[Amir]

In D138245#4057419, @aeubanks wrote:

59bc64c667f3e1fb724a4180ed2e6c78857d918e

Thanks! Do you have a buildbot running with non-assert build mode?

[aeubanks]

In D138245#4057647, @Amir wrote:

In D138245#4057419, @aeubanks wrote:

59bc64c667f3e1fb724a4180ed2e6c78857d918e

Thanks! Do you have a buildbot running with non-assert build mode?

Chrome clang packaging recently started building bolt (for bootstrapping clang, plus experimentation) and our official toolchain releases build without asserts and run check-all
(I can provide links to some builds if you want but right now the process is fairly ad hoc)

bolt/test/X86/jt-symbol-disambiguation-3.s

+# In this test case, we reproduce the behavior seen in gcc where the
+# base address of a jump table is decremented by some number and ends up
+# at the exact addess of a jump table from another function. After
+# linking, the instruction references another jump table and that
+# confuses BOLT.
+# We repro here the following issue:
+# Before assembler: Instruction operand is: jumptable - 32
+# After linking:    Instruction operand is: another_jumptable
+
+# REQUIRES: system-linux
+
+# XFAIL: *
+
+# RUN: llvm-mc -filetype=obj -triple x86_64-unknown-unknown %s -o %t.o
+# RUN: llvm-strip --strip-unneeded %t.o
+# RUN: %clang %cflags -no-pie -nostartfiles -nostdlib -lc %t.o -o %t.exe -Wl,-q
+
+# RUN: llvm-bolt %t.exe -o %t.exe.bolt --relocs=1 --lite=0 \
+# RUN:   --reorder-blocks=reverse
+
+# Useful when manually testing this. Currently we just check that
+# the test does not cause BOLT to assert.
+# COM: %t.exe.bolt 1 2
+
+  .file "jt-symbol-disambiguation-3.s"
+  .text
+
+# ----
+# Func foo contains a jump table whose start is colocated with a
+# jump table reference in another function. However, the other function
+# does not use the first entries of it and is merely doing arithmetics
+# to save the creation of unused first entries.
+# ----
+  .globl foo
+  .type foo, @function
+foo:
+  .cfi_startproc
+  xor    %rax,%rax
+  cmpq   $3, %rdi
+  ja     .LBBAD
+  jmpq   *.JT1(,%rdi,8)
+.LBB1:
+  movl   $0x4,%eax
+  jmp    .LBB5
+.LBB2:
+  movl   $0x5,%eax
+  jmp    .LBB5
+.LBB3:
+  movl   $0x6,%eax
+  jmp    .LBB5
+.LBB4:
+  movl   $0x7,%eax
+.LBB5:
+  retq
+.LBBAD:
+  mov    $1, %rdi
+  callq  exit@PLT
+  retq
+  .cfi_endproc
+  .size foo, .-foo
+
+# ----
+# Func _start scans an object with indexed access using %rax * 8 as an
+# index. However, %rax is known to be at least one, so the compiler
+# loads the pointer for the base address as object - 8 instead of just
+# object.
+# ----
+  .globl _start
+  .type _start, @function
+_start:
+  .cfi_startproc
+  movq   (%rsp), %rdi
+  callq  foo
+  movq   $1, %rdi
+  cmpq   $7, %rax
+  ja     .LBB10
+  # Here the compiler uses the knowledge that the first four entries
+  # of the jump table are not accessed and subtracts 32 from the base
+  # address of it, so it doesn't have to allocate four unused entries in
+  # memory. Unfortunately this can confuse BOLT since it ends up being a
+  # direct reference to JT1, after linker is done.
+  jmpq   *.JT2-32(,%rax,8)
+.LBB6:
+  xorq   %rdi, %rdi
+  jmp .LBB10
+.LBB7:
+  xorq   %rdi, %rdi
+  jmp .LBB10
+.LBB8:
+  xorq   %rdi, %rdi
+  jmp .LBB10
+.LBB9:
+  xorq   %rdi, %rdi
+  jmp .LBB10
+.LBB10:
+  callq exit@PLT
+  retq
+  .cfi_endproc
+  .size _start, .-_start
+
+# ----
+# Data section
+# ----
+  .section .rodata,"a",@progbits
+  .p2align 3
+.JT1:
+  .quad .LBB1
+  .quad .LBB2
+  .quad .LBB3
+  .quad .LBB4
+.JT2:
+  .quad .LBB6
+  .quad .LBB7
+  .quad .LBB8
+  .quad .LBB9