Re: Really, really const

[Andrew Haley <aph at redhat dot com>]

Gabriel Dos Reis writes:
 > Andrew Haley <aph@redhat.com> writes:
 > 
 > | So, I wonder why gcc reads the memory twice.
 > 
 > Maybe is it because GCC is treating a as a pointer of type "const int*"
 > instead of an array of "const int"?  That early decay might be
 > pessimizing. 

Maybe.  I just tried 3.2.2 and it doesn't read the memory twice:

foo:
        pushl   %ebx
        subl    $8, %esp
        movl    a, %ebx
        sall    $1, %ebx
        call    f
        addl    $8, %esp
        movl    %ebx, %eax
        popl    %ebx
        ret

but mainline does:

foo:
        pushl   %ebx
        subl    $8, %esp
        movl    a, %ebx
        call    f
        movl    a, %eax
        addl    $8, %esp
        addl    %eax, %ebx
        movl    %ebx, %eax
        popl    %ebx
        ret

So this looks like a regression.
  
Andrew.