Re: [PATCH] handle folded nonconstant array bounds [PR101702]

[Marek Polacek <polacek@redhat.com>]

On Tue, Nov 16, 2021 at 05:32:00PM -0700, Martin Sebor via Gcc-patches wrote:
> -Warray-parameter and -Wvla-parameter assume that array bounds
> in function parameters are either constant integers or variable,
> but not something in between like a cast of a constant that's
> not recognized as an INTEGER_CST until we strip the cast from
> it.  This leads to an ICE as the the internal checks fail.
> 
> The attached patch fixes the problem by stripping the casts
> earlier than before, preventing the inconsistency.  In addition,
> it also folds the array bound, avoiding a class of false
> positives and negatives that not doing so would lead to otherwise.
> 
> Tested on x86_64-linux.
> 
> Martin

> Handle folded nonconstant array bounds [PR101702]
> 
> PR c/101702 - ICE: in handle_argspec_attribute, at c-family/c-attribs.c:3623
> 
> gcc/c/ChangeLog:
> 
> 	PR c/101702
> 	* c-decl.c (get_parm_array_spec): Strip casts earlier and fold array
> 	bounds before deciding if they're constant.
> 
> gcc/testsuite/ChangeLog:
> 
> 	PR c/101702
> 	* gcc.dg/Warray-parameter-11.c: New test.
> 
> diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c
> index 186fa1692c1..63d806a84c9 100644
> --- a/gcc/c/c-decl.c
> +++ b/gcc/c/c-decl.c
> @@ -5866,6 +5866,12 @@ get_parm_array_spec (const struct c_parm *parm, tree attrs)
>        if (pd->u.array.static_p)
>  	spec += 's';
>  
> +      if (!INTEGRAL_TYPE_P (TREE_TYPE (nelts)))
> +	/* Avoid invalid NELTS.  */
> +	return attrs;
> +
> +      STRIP_NOPS (nelts);
> +      nelts = c_fully_fold (nelts, false, nullptr);

STRIP_NOPS before a call to c_fully_fold looks sort of weird, but I see
it's needed to prevent bogus warnings in Wvla-parameter-12.c:

void f2ci_can (const int m, char a[m]);
void f2ci_can (int n,       char a[n])

OK for trunk then.

>        if (TREE_CODE (nelts) == INTEGER_CST)
>  	{
>  	  /* Skip all constant bounds except the most significant one.
> @@ -5883,13 +5889,9 @@ get_parm_array_spec (const struct c_parm *parm, tree attrs)
>  	  spec += buf;
>  	  break;
>  	}
> -      else if (!INTEGRAL_TYPE_P (TREE_TYPE (nelts)))
> -	/* Avoid invalid NELTS.  */
> -	return attrs;
>  
>        /* Each variable VLA bound is represented by a dollar sign.  */
>        spec += "$";
> -      STRIP_NOPS (nelts);
>        vbchain = tree_cons (NULL_TREE, nelts, vbchain);
>      }
>  
> diff --git a/gcc/testsuite/gcc.dg/Warray-parameter-11.c b/gcc/testsuite/gcc.dg/Warray-parameter-11.c
> new file mode 100644
> index 00000000000..8ca1b55bd28
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/Warray-parameter-11.c
> @@ -0,0 +1,24 @@
> +/* PR c/101702 - ICE on invalid function redeclaration
> +   { dg-do compile }
> +   { dg-options "-Wall" } */
> +
> +typedef __INTPTR_TYPE__ intptr_t;
> +
> +#define copysign(x, y) __builtin_copysign (x, y)
> +
> +void f0 (double[!copysign (~2, 3)]);
> +
> +void f1 (double[!copysign (~2, 3)]);
> +void f1 (double[1]);                    // { dg-warning "-Warray-parameter" }
> +
> +void f2 (int[(int)+1.0]);
> +void f2 (int[(int)+1.1]);
> +
> +/* Also verify that equivalent expressions don't needlessly cause false
> +   positives or negatives.  */
> +struct S { int a[1]; };
> +extern struct S *sp;
> +
> +void f3 (int[(intptr_t)((char*)sp->a - (char*)sp)]);
> +void f3 (int[(intptr_t)((char*)&sp->a[0] - (char*)sp)]);
> +void f3 (int[(intptr_t)((char*)&sp->a[1] - (char*)sp)]);   // { dg-warning "-Warray-parameter" }


Marek