gcc 3.4.2 stack variable lifetime analysis

[Jakub Jelinek]

On Wed, May 04, 2005 at 07:22:12AM -0700, Earl Chew wrote:
> Can anyone tell me if there is a patch for this problem?

Yes, there is:
ftp://sources.redhat.com/pub/gcc/releases/gcc-4.0.0/diffs/gcc-3.4.3-4.0.0.diff.bz2

FYI, this is PR middle-end/9997

> Consider:
> 
>     void bar(char*);
> 
>     void foo(int x)
>     {
>         if (x) { char y[4096]; bar(y); }
>         else   { char z[4096]; bar(z); }
>     }
> 
> Cygwin gcc 3.4.2 -O2 yields:
> 
>         pushl   %ebp
>         movl    $8216, %eax   /* Should be about 4k */
>         movl    %esp, %ebp
>         call    __alloca
> 
> PPC cross compiler 3.4.2 -O2 yields:
> 
>         cmpwi 7,3,0
>         mflr 0
>         stwu 1,-8208(1)      /* Should be about 4k */

	Jakub