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From: Bernd Linsel <bl1-thispartdoesnotbelonghere@gmx.com>
Newsgroups: comp.arch
Subject: Re: Computer architects leaving Intel...
Date: Sat, 31 Aug 2024 13:58:46 +0200
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On 31.08.24 13:26, Thomas Koenig wrote:
> So, sorry for the too-quick examples earlier...
> 
> What about
> 
> int foo (int a)
> {
>    return a + 1;
> }
> 
> or
> 
> int foo(int *a)
> {
>    return *a;
> }
> 
> Both can exhibit undefined behavior, and for both it
> is impossible for the compiler to tell at compile-time.

So the compiler should just compile both functions (gcc 12.2.0 with -O3 
does):

$ gcc -Wall -Wextra -Wpedantic -O3 -xc -std=gnu11 -c - -o foo.o
int foo(int a)
{
     return a + 1;
}

int bar(int *a)
{
     return *a;
}
^D

$ objdump -d foo.o

foo.o:     file format elf64-x86-64


Disassembly of section .text:

0000000000000000 <foo>:
    0:   8d 47 01                lea    0x1(%rdi),%eax
    3:   c3                      ret
    4:   66 66 2e 0f 1f 84 00    data16 cs nopw 0x0(%rax,%rax,1)
    b:   00 00 00 00
    f:   90                      nop

0000000000000010 <bar>:
   10:   8b 07                   mov    (%rdi),%eax
   12:   c3                      ret

All as expected.

What I don't want is that the compiler makes assumptions, concludes UB, 
feels entitled to compile whatever it wants and deliver rubbish without 
telling about it.

-- 
Bernd Linsel