Re: [PATCH] bitintlower: Fix memmove source operand in finish_arith_overflow [PR126939]

On Wed, Aug 19, 2026 at 07:29:05AM -0500, Manjunath S Matti wrote:
> Bootstrapped and regression tested on powerpc64-linux (-m32/-m64), s390 and
> powerpc64le-linux.
> 
> finish_arith_overflow builds a memmove call to shift the result of a
> double-width multiplication down inside the destination object, on
> big-endian targets where the computed value occupies more limbs than
> the destination.
> 
> The destination argument correctly takes the address of OBJ, but SRC is
> a MEM_REF, that is a value of array type, and it is passed directly as
> memmove's second argument, which is a pointer.  Wrap it in
> build_fold_addr_expr so that the address is passed instead.  Since
> build_fold_addr_expr of a MEM_REF folds back to the pointer, no
> dereference is materialised.
> 
> The affected code is guarded by bitint_big_endian, and is only reached
> for widths whose value needs more limbs than the destination object,
> that is huge _BitInt operands of __builtin_{add,sub,mul}_overflow, so
> it needs a big-endian target with _BitInt support to be exercised at
> all.  It is being hit now that _BitInt is being enabled for powerpc
> (PR117584).
> 
> Existing coverage is sufficient: on powerpc64 big-endian this fixes
> gcc.dg/torture/bitint-93.c and bitint-94.c at -O0 and -O2, and
> gcc.dg/torture/bitint-32.c through bitint-37.c at -O0.  No new test is
> added.
> 
> 2026-08-19  Manjunath Matti  <[email protected]>
> 
> PR middle-end/126939

This PR line should be also indented by a tab.
Otherwise LGTM, I don't see you in write approval, shall I commit this
for you?

> gcc/
> 	* gimple-lower-bitint.cc (bitint_large_huge::finish_arith_overflow):
> 	Take the address of the memmove source operand.
> 
> diff --git a/gcc/gimple-lower-bitint.cc b/gcc/gimple-lower-bitint.cc
> index 52d0acad249..e36534ba13d 100644
> --- a/gcc/gimple-lower-bitint.cc
> +++ b/gcc/gimple-lower-bitint.cc
> @@ -4594,8 +4594,9 @@ bitint_large_huge::finish_arith_overflow (tree var, tree obj, tree type,
>  			     build_fold_addr_expr (unshare_expr (obj)), off);
>  	  g = gimple_build_call (fn, 3,
>  				 build_fold_addr_expr (unshare_expr (obj)),
> -				 src, build_int_cst (size_type_node,
> -						     obj_nelts * m_limb_size));
> +				 build_fold_addr_expr (src),
> +				 build_int_cst (size_type_node,
> +						obj_nelts * m_limb_size));
>  	  insert_before (g);
>  	}
>        if (orig_obj == NULL_TREE && obj)
> -- 
> 2.52.0

	Jakub