Subject: Re: [PATCH 5/7] xdiff: use GALLOC_GROW(), not XDL_ALLOC_GROW()

From: Phillip Wood <[email-masked]>
Date: Mon, 11 Jul 2022 11:13:06 +0100

Hi Ævar

On 08/07/2022 15:20, Ævar Arnfjörð Bjarmason wrote:
> Replace the recently introduced XDL_ALLOC_GROW() with invocations of
> the GALLOC_GROW() from git-shared-util.h.
> 
> As this change shows the macro + function indirection of
> XDL_ALLOC_GROW() is something we needed only because the two callsites
> we used it in wanted to use it as an expression, and we thus had to
> pass the "sizeof" down.
> 
> Let's just check the value afterwards instead, which allows us to use
> the shared macro, we can also remove xdl_reallo(), this was its last
> user.

I don't think this expression->statement change is an improvement. This 
change also removes the overflow checks that are present in 
XDL_ALLOC_GROW() and fails to free the old allocation when realloc() 
fails. It is not a like for like replacement.

Best Wishes

Phillip

> 
> Signed-off-by: Ævar Arnfjörð Bjarmason <[email-masked]>
> ---
>   xdiff/xdiff.h    |  1 -
>   xdiff/xmacros.h  | 11 -----------
>   xdiff/xprepare.c |  8 +++++---
>   xdiff/xutils.c   | 17 -----------------
>   xdiff/xutils.h   |  2 --
>   5 files changed, 5 insertions(+), 34 deletions(-)
> 
> diff --git a/xdiff/xdiff.h b/xdiff/xdiff.h
> index 72e25a9ffa5..832cf9d977e 100644
> --- a/xdiff/xdiff.h
> +++ b/xdiff/xdiff.h
> @@ -121,7 +121,6 @@ typedef struct s_bdiffparam {
>   
>   #define xdl_malloc(x) xmalloc(x)
>   #define xdl_free(ptr) free(ptr)
> -#define xdl_realloc(ptr,x) xrealloc(ptr,x)
>   
>   void *xdl_mmfile_first(mmfile_t *mmf, long *size);
>   long xdl_mmfile_size(mmfile_t *mmf);
> diff --git a/xdiff/xmacros.h b/xdiff/xmacros.h
> index 75506bdf17e..6a6b3057375 100644
> --- a/xdiff/xmacros.h
> +++ b/xdiff/xmacros.h
> @@ -48,15 +48,4 @@ do { \
>   	(v) = (unsigned long) __p[0] | ((unsigned long) __p[1]) << 8 | \
>   		((unsigned long) __p[2]) << 16 | ((unsigned long) __p[3]) << 24; \
>   } while (0)
> -
> -/*
> - * Ensure array p can accommodate at least nr elements, growing the
> - * array and updating alloc (which is the number of allocated
> - * elements) as necessary. Frees p and returns -1 on failure, returns
> - * 0 on success
> - */
> -#define XDL_ALLOC_GROW(p, nr, alloc)	\
> -	(-!((nr) <= (alloc) ||		\
> -	    ((p) = xdl_alloc_grow_helper((p), (nr), &(alloc), sizeof(*(p))))))
> -
>   #endif /* #if !defined(XMACROS_H) */
> diff --git a/xdiff/xprepare.c b/xdiff/xprepare.c
> index d6cbee32a2a..4182d9e1c0a 100644
> --- a/xdiff/xprepare.c
> +++ b/xdiff/xprepare.c
> @@ -128,8 +128,9 @@ static int xdl_classify_record(unsigned int pass, xdlclassifier_t *cf, xrecord_t
>   			return -1;
>   		}
>   		rcrec->idx = cf->count++;
> -		if (XDL_ALLOC_GROW(cf->rcrecs, cf->count, cf->alloc))
> -				return -1;
> +		GALLOC_GROW(cf->rcrecs, cf->count, cf->alloc);
> +		if (!cf->rcrecs)
> +			return -1;
>   		cf->rcrecs[rcrec->idx] = rcrec;
>   		rcrec->line = line;
>   		rcrec->size = rec->size;
> @@ -187,7 +188,8 @@ static int xdl_prepare_ctx(unsigned int pass, mmfile_t *mf, long narec, xpparam_
>   		for (top = blk + bsize; cur < top; ) {
>   			prev = cur;
>   			hav = xdl_hash_record(&cur, top, xpp->flags);
> -			if (XDL_ALLOC_GROW(recs, nrec + 1, narec))
> +			GALLOC_GROW(recs, nrec + 1, narec);
> +			if (!recs)
>   				goto abort;
>   			if (!(crec = xdl_cha_alloc(&xdf->rcha)))
>   				goto abort;
> diff --git a/xdiff/xutils.c b/xdiff/xutils.c
> index a6f10353cff..c0cd5338c4e 100644
> --- a/xdiff/xutils.c
> +++ b/xdiff/xutils.c
> @@ -436,20 +436,3 @@ int xdl_fall_back_diff(xdfenv_t *diff_env, xpparam_t const *xpp,
>   
>   	return status;
>   }
> -
> -void* xdl_alloc_grow_helper(void *p, long nr, long *alloc, size_t size)
> -{
> -	void *tmp = NULL;
> -	size_t n = ((LONG_MAX - 16) / 2 >= *alloc) ? 2 * *alloc + 16 : LONG_MAX;
> -	if (nr > n)
> -		n = nr;
> -	if (SIZE_MAX / size >= n)
> -		tmp = xdl_realloc(p, n * size);
> -	if (tmp) {
> -		*alloc = n;
> -	} else {
> -		xdl_free(p);
> -		*alloc = 0;
> -	}
> -	return tmp;
> -}
> diff --git a/xdiff/xutils.h b/xdiff/xutils.h
> index fd0bba94e8b..7ae3f897bef 100644
> --- a/xdiff/xutils.h
> +++ b/xdiff/xutils.h
> @@ -42,7 +42,5 @@ int xdl_emit_hunk_hdr(long s1, long c1, long s2, long c2,
>   int xdl_fall_back_diff(xdfenv_t *diff_env, xpparam_t const *xpp,
>   		       int line1, int count1, int line2, int count2);
>   
> -/* Do not call this function, use XDL_ALLOC_GROW instead */
> -void* xdl_alloc_grow_helper(void* p, long nr, long* alloc, size_t size);
>   
>   #endif /* #if !defined(XUTILS_H) */