[Bug tree-optimization/51513] Only partially optimizes away __builtin_unreachable switch default case

[mirq-gccboogs at rere dot qmqm.pl]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51513

Michał Mirosław <mirq-gccboogs at rere dot qmqm.pl> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mirq-gccboogs at rere dot qmqm.pl

--- Comment #12 from Michał Mirosław <mirq-gccboogs at rere dot qmqm.pl> ---
Created attachment 48236
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48236&action=edit
testcase

This bug reoccurred in gcc-8. gcc-7 and gcc-9+ seem not affected.

$ gcc-8 -O3 -S b.c -o -
[...]
foo:
.LFB0:
        .cfi_startproc
        cmpl    $1, %edi
        jne     .L10
        movslq  %esi, %rsi
        leaq    foz(%rip), %rax
        movl    (%rax,%rsi,4), %eax
        movl    %eax, (%rdx)
        xorl    %eax, %eax
        ret
        .p2align 4,,10
        .p2align 3
.L10:
        cmpl    $2, %edi
        jne     .L11
.L3:
        movslq  %esi, %rsi
        leaq    baz(%rip), %rax
        movl    (%rax,%rsi,4), %eax
        movl    %eax, (%rdx)
        xorl    %eax, %eax
        ret
        .p2align 4,,10
        .p2align 3
.L11:
        testl   %edi, %edi
        je      .L3
        .cfi_endproc
[...]

$ gcc-8 -O -S b.c -o -
[...]
foo:
.LFB0:
        .cfi_startproc
        cmpl    $1, %edi
        je      .L2
        cmpl    $2, %edi
        je      .L3
        testl   %edi, %edi
        jne     .L4
.L3:
        movslq  %esi, %rsi
        leaq    baz(%rip), %rax
        movl    (%rax,%rsi,4), %eax
        movl    %eax, (%rdx)
.L5:
        movl    $0, %eax
        ret
.L2:
        movslq  %esi, %rsi
        leaq    foz(%rip), %rax
        movl    (%rax,%rsi,4), %eax
        movl    %eax, (%rdx)
        jmp     .L5
.L4:
        .cfi_endproc