[llvm] [BOLT][AArch64] Do not crash on authenticated branch instructions (PR #129898)

[Alexey Moksyakov via llvm-commits]

yavtuk wrote:

> Could you please provide an example of such JT lowering - using "branch with link" looks quite counter-intuitive at first.

@atrosinenko the simplified version with array of functions pointers,
pattern can be different but blr the latest instruction

clang -fjump-tables
gcc --param=case-values-threshold=4

`
int __attribute__ ((noinline)) option0() {
        printf("Function 1 called\n");
        return 1;
}

int (*jumpTable[6])(void) = { option0, option1, option2, option3, option4, option5 };

void __attribute__ ((noinline)) handleOptionJumpTable(int option) {
    const int result = jumpTable[option]();
    printf("result %d\n", result);
}
`

`
objdump --disassemble=handleOptionJumpTable --no-addresses --no-show-raw-insn ./jt

./jt:     file format elf64-littleaarch64


Disassembly of section .text:
<main>
        ldur    w0, [x29, #-8]
        bl      <handleOptionJumpTable>

<handleOptionJumpTable>:
        prologue

        adrp    x8, jumpTable
        ldr     x8, [x8, #3656]
        ldr     x8, [x8, x0, lsl #3]
        blr     x8

        epilogue
        ret
`


https://github.com/llvm/llvm-project/pull/129898