[Bug middle-end/59521] __builtin_expect not effective in switch

["marxin at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59521

--- Comment #5 from Martin Liška <marxin at gcc dot gnu.org> ---
Ok, your patch is definitely needed to properly propagate the builtin
probability to a proper edge. Apart from that I added code that preserves that
probability incombine_predictions_for_bb. Having that we're quite close:

$ ./xgcc -B. ~/Programming/testcases/pr59521.c -O2 -c -S
-fdump-tree-optimized=/dev/stdout

;; Function f (f, funcdef_no=11, decl_uid=2306, cgraph_uid=11, symbol_order=11)

Removing basic block 7
f (int ch)
{
  <bb 2> [100.00%] [count: INV]:
  switch (ch_4(D)) <default: <L3> [3.33%] [count: INV], case 3: <L0> [3.33%]
[count: INV], case 42: <L1> [3.33%] [count: INV], case 333: <L2> [90.00%]
[count: INV]>

But still there's a missing piece that will rearrange switch statement so that
case 333 will be first:

f:
.LFB11:
        .cfi_startproc
        cmpl    $42, %edi
        je      .L3
        cmpl    $333, %edi
        jne     .L8
        movl    $.LC2, %edi
        jmp     puts

Can you please Yuri take a look?