[PATCH] Fix PR 101453: ICE with optimize and large integer constant

[Jakub Jelinek]

On Thu, Jul 15, 2021 at 06:59:17PM -0700, apinski--- via Gcc-patches wrote:
> From: Andrew Pinski <apinski@marvell.com>
> 
> Every base 10 digit will take use ~3.32 bits to represent. So for
> a 64bit signed integer, it is 20 characters. The buffer was only
> 20 so it did not fit; add in the null character and "-O" part,
> the buffer would be 3 bytes too small.
> 
> Instead of just increasing the size of the buffer, I decided to
> calculate the size at compile time and use constexpr to get a
> constant for the size.
> Since GCC is written in C++11, using constexpr is the best way
> to force the size calculated at compile time.
> 
> OK? Bootstrapped and tested on x86_64-linux with no regressions.
> 
> gcc/c-family/ChangeLog:
> 
> 	PR c/101453
> 	* c-common.c (parse_optimize_options): Use the correct
> 	size for buffer.

The formatting is wrong (lots of spaces missing) and we aren't that space
constrained that we need to use floating point in the calculations.
Other places in the gcc just multiply sizeof by 3, which isn't enough
for -128..128 char, but long has must have wider range than that.
So just char buffer[sizeof (long) * 3 + 3]; ?
Or at least use HOST_BITS_PER_LONG instead of sizeof(long)*CHAR_BIT and
avoid the double calculation, so
  char buffer[HOST_BITS_PER_LONG / 3 + 4];

> ---
>  gcc/c-family/c-common.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
> index 20ec26317c5..4c5b75a9548 100644
> --- a/gcc/c-family/c-common.c
> +++ b/gcc/c-family/c-common.c
> @@ -5799,7 +5799,9 @@ parse_optimize_options (tree args, bool attr_p)
>  
>        if (TREE_CODE (value) == INTEGER_CST)
>  	{
> -	  char buffer[20];
> +	  constexpr double log10 = 3.32;
> +	  constexpr int longdigits = ((int)((sizeof(long)*CHAR_BIT)/log10))+1;
> +	  char buffer[longdigits + 3];
>  	  sprintf (buffer, "-O%ld", (long) TREE_INT_CST_LOW (value));
>  	  vec_safe_push (optimize_args, ggc_strdup (buffer));
>  	}
> -- 
> 2.27.0

	Jakub